Myostatin and irisin levels in predicting the outcome of patients with systemic inflammation: A prospective observational study

Myostatin and irisin levels in predicting the outcome of patients with systemic inflammation: A prospective observational study | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Myostatin and irisin levels in predicting the outcome of patients with systemic inflammation: A prospective observational study Otakar Psenicka, Tomas Brutvan, Hana Vitkova, Zuzana Krsakova, and 3 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-8991519/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 15 You are reading this latest preprint version Abstract Background : Systemic inflammatory response syndrome (SIRS) is associated with changes in muscle metabolism. Resulting muscle weakness is linked with adverse outcomes, e.g. prolonged mechanical ventilation, length of hospital stay and increased mortality. Skeletal muscles produce myokines, which may contribute to the development of muscle weakness. The aim of this study was to assess the potential utility of selected myokine levels in predicting the prognosis of patients with SIRS. Methods : This was a prospective observational study. Levels of myostatin and irisin, selected anthropometric, laboratory and muscle parameters (ultrasound measured thickness of quadriceps muscle US QMT, hand grip strength HGS, lean body mass LBM) were recorded within 48h from admission and at the day 10 of hospital stay. Control group consisted of healthy individuals. Results : A total of 54 participants (30 in the study group and 24 controls) were included in the study. Primary outcome (LoS=length of hospital stay) was not significantly different in probands with higher or lower myostatin or irisin levels (p = 0.59 and p = 0.659). Myostatin and irisin levels in control group were significantly lower than in study cohort (11.86 µg/L vs. 29.04 µg/mL, p = < 0.001 and 33.70 µg/L vs. 41.80 ug/L, p = 0.015). Irisin levels were higher in women than in men both in probands (p = 0.028) and controls (p = 0.001). There was a significant correlation between myostatin and CRP and NLR (p = 0.001; p = 0.021) and between irisin and BMI (p = 0.001). Both myostatin (p = 0.008) and irisin (p = 0.019) levels were associated with change of US QMT. QMT correlated with LBM (p = 0.002) and HGS (p = 0.002). Conclusions : There was no significant association of myokine levels with LoS. A significant correlation between baseline myokines levels and US QMT change was present which suggest their potential role in muscle metabolism in critically ill patients. US QMT may be a useful method to monitor muscle wasting. myokines critical illness systemic inflammation muscle ultrasound Figures Figure 1 Figure 2 Figure 3 Introduction Muscle weakness develops in approximately half of critically ill patients ( 1 ). Among those with sepsis or systemic inflammatory response syndrome (SIRS) of other etiologies, its prevalence is even higher, up to 75% ( 2 ). The pathogenesis of intensive care unit-acquired weakness (ICU-AW) is multifactorial. General factors of critical illness, such as persistent catabolic processes, immobilization, mechanical ventilation etc., can contribute to the development of ICU-AW. On the other hand, complex alterations in muscle physiology and biochemistry occur at the molecular level. These include mitochondrial dysfunction, increased production of reactive oxygen species, impaired autophagy, and changes in membrane ion channel function ( 3 ). These processes accelerate muscle atrophy and reduce muscle function, leading to prolonged mechanical ventilation, difficult rehabilitation, longer hospital stays, and increased morbidity and mortality ( 4 ). Same mechanisms are also a key driver to long-term functional impairment persisting after discharge from intensive care, referred to as post-intensive care syndrome (PICS) ( 5 ). Skeletal muscle itself may be involved in the complex pathogenesis of ICU-AW through the release of specific signalling molecules, so-called myokines . These peptide- or protein-based cytokines have autocrine and paracrine effects on muscle fibres and surrounding structures (satellite cells, fascia, bone), while upon release into the circulation they also exert endocrine effects on distant tissues ( 6 ). The most extensively studied effects relate to glucose metabolism and adipose tissue regulation; current research also focuses on their impact on the brain and gastrointestinal tract ( 7 ). Although several hundred myokines have been described to date, detailed information about their structure and function exist only for a few dozen. The first identified myokine was myostatin ( 8 ). Experimental models demonstrate that myostatin inhibits muscle protein synthesis, accelerates protein degradation, and suppresses both muscle growth and differentiation. Myostatin plasma levels are reduced after both aerobic and anaerobic exercise ( 9 ). Muscular animal models with myostatin deficiency have been described ( 10 ), as well as a case report of a human infant presenting with pronounced muscularity and a confirmed homozygous mutation in the myostatin gene ( 11 ). Myostatin inhibitors have been considered as promising therapeutic candidates for the treatment of sarcopenia and genetic muscular dystrophies, supported by encouraging results from animal studies. In humans, however, no molecule has yet demonstrated a significant clinical benefit ( 12 ). Clinical studies in humans have further reported inconsistent findings regarding circulating myostatin levels across different disease states. ( 13 , 14 ) For instance, Amor et al. ( 13 ) reported elevated circulating myostatin levels in obesity, correlating with insulin resistance and suggesting a role in chronic metabolic dysfunction. In contrast, Wirtz et al. ( 14 ) observed that low myostatin serum levels in critically ill patients were associated with poor outcomes, indicating that acute systemic inflammation and severe illness may alter myostatin regulation differently than chronic disease states. Irisin is an exercise-induced myokine that influences muscle hypertrophy, regulation of thermogenesis, and the browning of white adipose tissue ( 15 ). Its circulating levels correlate with various clinical parameters in obese individuals and patients with type 2 diabetes ( 16 ). Yet other studies have shown inconsistent and sometimes contradictory findings, particularly regarding its relationship with muscle mass and muscle strength. While lower irisin levels have been reported in obesity and type 2 diabetes, suggesting an association with metabolic dysfunction ( 16 ), studies in older adults and postmenopausal women have demonstrated variable associations between circulating irisin, muscle mass, and functional measures of muscle strength. In older adults with sarcopenia, lower irisin concentrations have been observed compared with healthy controls ( 17 ), while another study reported an inverse correlation between irisin levels, CT-assessed thigh muscle thickness, and hand-grip strength ( 18 ). Muscle dysfunction in patients with systemic inflammation can be objectively assessed using electromyography (EMG) ( 19 ). However, due to its invasive nature, EMG is rarely used in this indication. Instead, non-invasive methods such as hand-grip strength or more complex MRC (Medical Research Council) score are more commonly applied in day-to-day practise ( 19 ). Functional performance assessments, including the six-minute walking test, the Timed Up & Go test or the Short Physical Performance Battery can be performed on cooperating patients ( 20 ). Muscle mass assessment with dual-energy X-ray absorptiometry DXA, computed tomography CT or magnetic resonance imaging MRI are dominantly used in research studies and are not routinely investigated in clinical setting ( 21 ). In recent years, bedside ultrasound of skeletal muscles has gained increasing use in the ICU due to its routine availability, non-invasiveness and good reproducibility. ( 22 ). Quadriceps muscle thickness (QMT) is the most commonly measured parameter. This assessment can be performed repeatedly during the course of illness to evaluate the degree of muscle loss and/or change in muscle quality. The decline of muscle thickness correlates with ICU-AW and with poor clinical outcomes ( 23 ). The aim of our study was to examine potential associations between circulating levels of selected myokines (myostatin, irisin) and outcomes in patients with systemic inflammatory states. We hypothesized that patients with higher myostatin and/or lower irisin concentrations at disease onset would experience worse outcomes, with the primary endpoint being length of hospital stay. Secondary analyses focused on correlations between myokine levels and additional parameters (laboratory and anthropometric parameters, muscle strength), as well as the potential role of bedside ultrasound of the thigh muscle in assessing catabolism and predicting outcomes. To date, most clinical investigations of selected myokines have been limited to animal models or highly specific patient groups. Prospective observational studies exploring the impact of myokines on hospital stay and functional outcomes in patients with systemic inflammation are to the best of our knowledge not yet available in the literature. Methodology This was a single-centre prospective observational pilot study. All patients admitted with an acute illness to the 3rd Department of Internal Medicine or the Department of Anaesthesiology, Resuscitation and Intensive Medicine at the General University Hospital in Prague were considered for enrolment. Eligible patients met the criteria for a systemic inflammatory response syndrome (SIRS), defined as the presence of at least two of the following: body temperature > 38°C or 90 bpm, respiratory rate > 20/min or PaCO₂ 12 × 10 6 /l, or leukopenia < 4 × 10 6 /l. A minimum expected hospital stay of five days was required for enrolment. (Note: SIRS criteria were used to enable inclusion of patients with non-septic conditions, such as acute pancreatitis.) Exclusion criteria included transfer from another hospital with a prior length of stay exceeding 48 hours, terminal illness (malignant or non-malignant), and pre-admission long-term immobility. Written informed consent was obtained from all participants. In cases where participants were temporarily unable to provide written consent due to their clinical condition, informed consent was obtained verbally or through affirmative non-verbal communication in the presence of a witness. For these participants, written informed consent was obtained as soon as their clinical condition allowed. Ethical approval was provided by the General University Hospital in Prague Ethics Commission, ID 38/23, 20/04/2023. The control group consisted of healthy individuals matched with age and sex where applicable. Controls were defined as individuals free of acute or chronic illnesses that could confound study outcomes. All controls underwent screening consisting of medical history and physical examination. Individuals were excluded for any autoimmune, inflammatory, cardiovascular, metabolic, or other systemic disease requiring treatment. Written informed consent was obtained from all controls. A total of 30 patients in a study group and 24 controls were included in the study from March 2023 to December 2024. Sample size was determined prior to study initiation based on feasibility considerations and expert statistician consultation. No formal a priori power calculation based on predefined effect sizes was performed. The primary outcome was length of hospital stay, defined as the number of days from hospital admission to discharge alive. Six patients died during the follow-up period and were therefore excluded from the analysis of the primary outcome, as length of hospital stay is not a defined or interpretable endpoint in non-survivors. In deceased patients, secondary outcomes and the composite outcome were analysed. Secondary outcomes included associations between baseline circulating myokine levels and 1) laboratory markers of inflammation and nutritional status; 2) anthropometric parameters and bioimpedance analysis; 3) handgrip strength; 4) ultrasound-derived measures of thigh muscle mass, as well as the prognostic value of these measures for clinical outcomes. Secondary outcomes were considered exploratory and hypothesis-generating. Also, the composite outcome (BAD) was defined a priori for exploratory purposes as a hospital length of stay (LoS) above the 75th percentile, or an ICU length of stay (LoS-ICU) above the 75th percentile, or transfer to a long-term care facility, or death. Immediately after enrolment, and no later than within 48 hours, blood samples were collected from participants in both the study and control groups to determine myostatin (MSTN ELISA Kit, Cat. No: MBS021687) and irisin (Human Irisin ELISA Kit, Cat. No: MBS706887) levels. Myokines were measured in paired serum samples, and the mean value of two measured concentrations was used for analysis. In the study group also laboratory markers of inflammation (CRP, procalcitonin, neutrophile to lymphocyte ratio NLR) and nutritional status (albumin, prealbumin) were assessed. Anthropometric parameters, muscle measurements and bioimpedance analysis (body weight, BMI, body fat percentage, lean body mass, handgrip strength, ultrasound-derived measures) were assessed in both study and control groups. Handgrip strength was evaluated using a portable dynamometer (Trailite TL-LSC 100), and quadriceps muscle thickness was measured by ultrasound UGEO HM70A (Samsung, Seoul, Korea.) In the study group, the same assessment was repeated on day 10 after admission. Ultrasound measurements were conducted with linear transducer (3–16 MHz) in musculoskeletal pre-set. The quadriceps femoris muscle of the dominant lower limb was used for the investigation. All measurements were conducted by the same investigator (OP) according to a predetermined protocol. Patients were lying supine with extended knees and toes pointing to the ceiling. As the exact point for the measurement, the one-third of the distance from cranial patella margin to anterior inferior iliac spine on the pelvis was determined [25]. Three measurements of total thickness of the muscle (i.e. rectus femoris and vastus intermedius (RF + VI)) were obtained and the average value was calculated and recorded. All statistical analyses were performed using STATISTICA version 12 (Statsoft Inc., Tulsa, OK, USA). Continuous variables were first tested for normality using the Shapiro–Wilk test. Homogeneity of variances between groups was assessed using Levene’s test. Normally distributed variables with equal variances were compared using the independent samples t -test. For non-normally distributed variables or in the presence of unequal variances, the Mann–Whitney U test was applied. Correlations between continuous variables were evaluated using Pearson’s correlation coefficient for normally distributed data or Spearman’s rank correlation coefficient for non-normally distributed data. Paired t-tests were used for within-group comparisons over time. All statistical tests were two-tailed, and a p -value < 0.05 was considered statistically significant. Given the exploratory nature of the secondary outcomes, no formal correction for multiple testing was applied. Data are expressed as mean ± standard deviation (SD) unless otherwise stated. The study protocol was approved by the Ethics Committee of General University Hospital in Prague. Results Study Group and Control Group The study group included 30 participants (mean age 67.9 years, range 24–89 years; 50% males) with mean weight 82.04 kg (± 18.34) and mean BMI 27.43 (± 5.59). The control group consisted of 24 participants (mean age of 35.9 years, range 27–54, 50% males). Mean weight was 75.86 kg (± 10.92) and BMI was 23.98 (± 2.47). Laboratory values and muscle parameters Table 1 presents baseline muscle and laboratory data of the study group and the control group. Table 2 presents the development of values in the study group on day 10. Table 1 Baseline characteristics of the study group and the control group. Handgrip (kg) Study group - Baseline Control group - Baseline 20.7 (± 9.89) 39.51 (± 8.80) US RF + VI (mm) 25.80 (± 5.83) 36.34 (± 8.05) Fat mass (%) 34.2 (± 9.65) 23.47 (± 7.67) LTM (kg 41.25 (± 10.59) 51.48 (± 10.63) Creatinine (umol/l) 151.63 (± 129.57) - CRP (mg/l) 271.47 (± 129.11) - PCT (ug/l) 23.67 (± 41.09) - Albumin (g/l) 29.72 (± 5.77) - NLR 18.64 (± 11.96) - Myostatin (ng/ml) 29.04 (± 13.25) 11.86 (± 9.12) Irisin (ng/ml) 41.80 (± 57.26) 33,70 (± 30.65) Table 2 Development of measured values in the study group on day 10 Handgrip (kg) Study group - Baseline Study group - Day 10 20.7 (± 9.89) 21.9 (± 8.68) US QMT (mm) 25.80 (± 5.83) 23.33 (± 6.24) Fat mass (%) 34.2 (± 9.65) 41 (± 14.18) LBM (kg) 41.25 (± 10.59) 40.61 (± 11.08) Creatinine (umol/l) 151.63 (± 129.57) 122.52 (± 139.37) CRP (mg/l) 271.47 (± 129.11) 76.3 (± 72.95) PCT (ug/l) 23.67 (± 41.09) 0.44 (± 0.25) Albumin (g/l) 29.72 (± 5.77) 27.52 (± 4.51) NLR 18.64 (± 11.96) 5.74 (± 3.09) Myostatin (ng/ml) 29.04 (± 13.25) 16.54 (± 10.47) Irisin (ng/ml) 41.80 (± 57.26) 81.72 (± 61.73) Myostatin and Irisin analysis The median myostatin concentration in the study cohort was 29.04 µg/mL, and the median irisin concentration was 41.80 µg/mL. Participants with myostatin levels below the median (n = 11) had a mean hospital stay of 25.73 days (± 21.04), those with higher myostatin levels (n = 13) had a mean hospital stay of 21.97 days (± 20.81). Patients with lower irisin levels (n = 10) had a mean hospital stay of 21.60 days (± 19.86), compared with 25.50 days (± 21.86) in those with higher irisin concentrations (n = 14), (Fig. 1 ). No significant differences were found between the two subgroups (p = 0.59 and p = 0.659 respectively.) Similarly, length of ICU stay was analysed with no significant differences found between groups with lower and higher myostatin or irisin (p = 0.76 and p = 0.62 respectively.) In the control group, mean myostatin and irisin levels were 11.86 µg/mL and 33.70 µg/mL, which were significantly lower than in the study cohort (p = < 0.001 and p = 0.015 respectively), (Fig. 2 .) Significantly higher irisin levels were observed in women compared with men, both among patients (89.03 vs. 43.91 µg/mL; p = 0.028) and controls (52.304 vs. 15.1 µg/mL; p = 0.001). No sex-related differences were found in myostatin concentrations. Secondary analysis As part of the secondary analyses, correlations were observed between irisin and BMI and LTM (p = 0.001 and p = 0.001 respectively), between myostatin and CRP (p = 0.001), and between myostatin and NLR (p = 0.021). Furthermore, both myokines correlated with the change in thigh muscle thickness assessed by ultrasound: myostatin showed a positive correlation (p = 0.008), whereas irisin showed a negative correlation (p = 0.019) (Fig. 3 ). Ultrasound-measured thigh muscle thickness was positively correlated with lean body mass (p = 0.002), and handgrip strength measured by dynamometry (p = 0.002). Discussion To the best of our knowledge, none of the studies published to date have investigated the association between myostatin and irisin, muscle dysfunction and subsequent outcomes in critically ill patients with such a comprehensive scope of assessed parameters as in our study. This multimodal approach to the development of muscle weakness and its impact on functional outcomes represents the main strength of the presented study. By introducing a control group, we found that the levels of both investigated myokines were significantly lower in the control group compared to the study group. This finding is consistent with previously published data in patients with chronic kidney disease [26], liver cirrhosis [27], and COPD [28], where elevated myostatin levels have been associated with worse prognosis. However, previous studies in critically ill patients have reported contradictory findings. For example, Wirtz et al. [14] reported higher mortality and morbidity in patients with lower myostatin levels. Our analysis also suggested a possible association between lower myostatin levels and worse composite outcome (due to the wide confidence interval and low statistical power of the study, this result should be interpreted with caution and confirmed in larger cohorts). Taken together, available evidence suggests that the prognostic significance of circulating myostatin is highly context dependent. While chronically elevated myostatin appears to contribute to muscle wasting and adverse outcomes in chronic diseases, low myostatin levels in acute critical illness may reflect exhausted myokine production and reduced muscle reserve [29]. Despite the relatively small sample size, a significant difference in irisin levels between sexes was observed, with higher concentrations in women than in men, both in the study cohort and in the control group. Higher irisin levels in women have been demonstrated in previous studies [30]. The exact underlying mechanism remains unclear but circulating estradiol levels and sex-related differences in the distribution of brown and white adipose tissue are likely contributing factors [31]. Rapid skeletal muscle loss within just a few days of systemic inflammation is a well-described phenomenon [4]. In our cohort, lean body mass decreased by 1,2 kg over a ten-day period, accompanied by an average reduction in ultrasound-measured quadriceps muscle thickness of 0,8 millimetres. A notable finding is the demonstrated correlation of both myokines with this change in quadriceps thickness. Our results indicate that lower baseline myostatin and higher baseline irisin were associated with less pronounced muscle loss over time. However, these associations should be interpreted as descriptive rather than casual. As highlighted by a recent scoping review [32], the relationships between myokines and muscle loss may vary in critically ill patients, especially depending on patient’s mobility and performed physical intervention. When relying on a single method to monitor muscle loss, the results may be unreliable. Both ultrasound muscle assessment and bioimpedance can be affected by systemic oedema [33]. Handgrip strength measurement demonstrates lower reliability in patients with reduced muscle strength and is often limited by poor cooperation in critically ill individuals [34]. In our cohort, we observed correlations between the different measurement modalities, however, methodological limitations of handgrip strength and bioimpedance may have influenced some associations. Nevertheless, ultrasound assessment of quadriceps muscle thickness appears to be a valuable tool for monitoring temporal changes, given its simplicity, bedside feasibility, and the routine availability of ultrasound devices in intensive care units. This study has several limitations. One is a relatively small sample size. A preliminary sample size was estimated (based on available data of myokine concentrations and average length of hospital stay in Czech Republic), but our data suggests, that even with much larger number of probands, the results would still be insignificant. Length of hospital stay is also not an ideal primary outcome, due to potential influence from other factors, e.g. availability of aftercare beds. Also, exclusion of patients who died during hospitalization from the primary outcome may have introduced survivor bias. There was also a substantial age difference between patients and controls. Given this age difference, between-group comparisons should be interpreted rather descriptively than as evidence of disease-specific effects. Despite given inclusion and exclusion criteria, residual confounding and heterogeneity of included patients related to age, comorbidities, disease severity and unmeasured metabolic or inflammatory factors could not be excluded. Significantly different levels of myostatin and irisin in healthy controls indicate that these factors could influence baseline myokine concentrations and thus the subsequent results. Some of the previously published studies demonstrated relatively rapid changes in myostatin levels during the post-insult period and their correlation with inflammatory parameters [35]. Therefore, the allowed time window of 48 from admission may also be a small limitation, as the exact timing of sample collection in relation to the onset and duration of the primary insult could therefore be crucial. A mild limitation of our study is also the methodology used for the ultrasound assessment of the thigh muscle. Ultrasound measurements were performed at two-thirds of the distance between the anterior inferior iliac spine and the superior border of the patella. Although this site may increase sensitivity for detecting peripheral muscle atrophy, it is less frequently used in previous literature compared with the mid-thigh position. As a result, direct comparison of absolute thickness values with other studies should be interpreted with caution. Conclusions The present paper reports data from a pilot observational study. The selected myokines, myostatin and irisin, were not associated with the primary outcome—length of hospital stay. Exploratory secondary analysis suggests that these myokines may reflect aspects of muscle metabolism within a multimodal approach to the management of critically ill patients. Ultrasound assessment of the thigh muscle appears to be a useful and easily applicable method for monitoring dynamic changes in muscle thickness and, potentially, muscle quality. Abbreviations BMI Body mass index CRP C–reactive protein DXA dual–energy X–ray absorptiometry EMG electromyography HGS hand grip strength ICU AW –intensive care unit–acquired weakness LBM Lean body mass LoS length of hospital stay MRC medical research council NLR neutrophile to leukocyte ratio PCT procalcitonin PICS post–intensive care syndrome SIRS systemic inflammatory response syndrome US QMT ultrasound measured thickness of quadriceps muscle Declarations Clinical trial number The study was not prospectively registered. Retrospective registration at ClinicalTrials.gov is currently in progress. The registration number will be added to the manuscript as soon as it becomes available . Ethics approval and consent to participate: The study was conducted in accordance with the Declaration of Helsinki and approved by the Ethics Committee of General University Hospital in Prague, ID 38/23(approval date: 20 April 2023). Informed consent was obtained from all subjects involved in the study. Competing interests: The authors declare no competing interests. Funding: This research and the APC was funded by MH CZ—DRO (General University Hospital in Prague—VFN), grant number 00064165. Author Contribution Conceptualization, O.P., T.B., Z.K., J.K. (Jan Kratky), J.S. and J.K. (Jarmila Krizova); methodology, O.P., J.S. and J.K. (Jarmila Krizova), software, O.P. and J.K. (Jarmila Krizova); formal analysis, O.P. and J.K. (Jarmila Krizova); investigation, O.P, T.B., Z.K., J.K. (Jan Kratky), J.S. and J.K. (Jarmila Krizova), resources, O.P., T.B., Z.K., J.K. (Jan Kratky), J.S. and J.K. (Jarmila Krizova); data curation, O.P., T.B., Z.K., J.K. (Jan Kratky), J.S. and J.K. (Jarmila Krizova); writing—original draft preparation, O.P. and J.K. (Jarmila Krizova); writing—review and editing, O.P., J.S. and J.K. (Jarmila Krizova); visualization, O.P. and J.K. (Jarmila Krizova); supervision, J.K. (Jarmila Krizova); project administration O.P., J.S. and J.K. (Jarmila Krizova); funding acquisition, O.P., J.S. and J.K. (Jarmila Krizova). All authors have read and agreed to the published version of the manuscript. Data Availability The datasets used and/or analysed during the current study are available from the corresponding author upon reasonable request. References Schefold JC, Weber-Carstens S et al. Muscular weakness and muscle wasting in the critically ill. J Cachexia Sarcopenia Muscle. 2020;11(6):1399–1412. Callahan LA, Supinski GS. Sepsis-induced myopathy. Crit Care Med. 2009;37(10 Suppl):S354-67 Vanhorebeek I, Latronico N, Van den Berghe G. ICU-acquired weakness. Intensive Care Med. 2020;46(4):637–653 Puthucheary Z.A., Sidhu P.S. et al. Acute Skeletal Muscle Wasting in Critical Illness. JAMA. 2013;310:1591–1600 Needham DM, Davidson J, Cohen H et al. Improving long-term outcomes after discharge from intensive care unit: report from a stakeholders' conference. Crit Care Med. 2012; 40(2): 502–9. Pedersen BK, Febbraio MA. Muscles, exercise and obesity: skeletal muscle as a secretory organ. Nat Rev Endocrinol. 2012;8(8):457–65 Blume GR, Royes LFF. Peripheral to brain and hippocampus crosstalk induced by exercise mediates cognitive and structural hippocampal adaptations. Life Sci. 2024;352:122799 McPherron AC, Lawler AM, Lee SJ. Regulation of skeletal muscle mass in mice by a new TGF-beta superfamily member. Nature. 1997;387(6628):83–90 Hittel DS, Kraus WE et al. Myostatin decreases with aerobic exercise and associates with insulin resistance. Med Sci Sports Exerc. 2010;42(11):2023–9 Kobayashi M, Kaneki M et al. Myostatin deficiency not only prevents muscle wasting but also improves survival in septic mice. Am J Physiol Endocrinol Metab. 2021;320(1):E150-E159. Schuelke M, Lee SJ et al. Myostatin mutation associated with gross muscle hypertrophy in a child. N Engl J Med. 2004;350(26):2682–8. Mariot V, Dumonceaux J et al. Downregulation of myostatin pathway in neuromuscular diseases may explain challenges of anti-myostatin therapeutic approaches. Nat Commun. 2017;8(1):1859. Amor M, Stulnig TM et al. Serum Myostatin is Upregulated in Obesity and Correlates with Insulin Resistance in Humans. Exp Clin Endocrinol Diabetes. 2019;127(8):550–556. Wirtz TH, Koch A et al. Low Myostatin Serum Levels Are Associated with Poor Outcome in Critically Ill Patients. Diagnostics (Basel). 2020;10(8):574. Waseem R, Islam A et al. FNDC5/Irisin: Physiology and Pathophysiology. Molecules. 2022;27(3):1118. Shoukry A, Khalifa A et al. Circulating serum irisin levels in obesity and type 2 diabetes mellitus. IUBMB Life. 2016;68(7):544–56 Chang JS, Kong ID et al. Circulating irisin levels as a predictive biomarker for sarcopenia: A cross-sectional community-based study. Geriatr Gerontol Int. 2017;17(11):2266–2273 Park, HS., Kim, H.C., Zhang, D. et al. The novel myokine irisin: clinical implications and potential role as a biomarker for sarcopenia in postmenopausal women. Endocrine 64, 341–348 (2019). Hermans G, Van den Berghe G. Clinical review: intensive care unit acquired weakness. Crit Care. 2015;19(1):274 Wu TT, Li H. Effects of a multilevel intervention of resistance training with or without beta-hydroxy-beta-methylbutyrate in medical ICU patients during entire hospitalisation: a four-arm multicentre randomised controlled trial. Crit Care. 2023;27(1):493. van der Steen-Dieperink MJMM, Koekkoek WAC, Kouw IWK. Sarcopenia and frailty in critical illness. Curr Opin Clin Nutr Metab Care. 2025;28(3):192–199. Looijaard W.G., Molinger J., Weijs P.J. Measuring and monitoring lean body mass in critical illness. Curr. Opin. Crit. Care. 2018;24:241–247 Zhang Y, Ma F et al. Development and validation of machine learning-based risk prediction models for ICU-acquired weakness: a prospective cohort study. Eur J Med Res. 2025;30(1):666. doi: 10.1186/s40001-025-02930-8 . Erratum in: Eur J Med Res. 2025;30(1):1158. Bone RC, Sibbald WJ et al. Definitions for sepsis and organ failure and guidelines for the use of innovative therapies in sepsis. The ACCP/SCCM Consensus Conference Committee. American College of Chest Physicians/Society of Critical Care Medicine. Chest. 1992;101(6):1644-55. Martín C.A.G., Zepeda E.M., Méndez O.A.L. Bedside Ultrasound Measurement of Rectus Femoris: A Tutorial for the Nutrition Support Clinician. J. Nutr. Metab. 2017;2017:2767232 Verzola D, Garibotto G et al. Apoptosis and myostatin mRNA are upregulated in the skeletal muscle of patients with chronic kidney disease. Kidney Int. 2011;79(7):773–82. Nishikawa H, Nishiguchi S et al. Elevated serum myostatin level is associated with worse survival in patients with liver cirrhosis. J Cachexia Sarcopenia Muscle. 2017;8(6):915–925. Ju CR, Chen RC. Serum myostatin levels and skeletal muscle wasting in chronic obstructive pulmonary disease. Respir Med. 2012;106(1):102–8. Sharma S, Patil AS. Myostatin's marvels: From muscle regulator to diverse implications in health and disease. Cell Biochem Funct. 2024;42(6):e4106 Zügel M, Schumann U et al. The role of sex, adiposity, and gonadectomy in the regulation of irisin secretion. Endocrine. 2016;54(1):101–110. Barbagallo F, Calogero AE et al. The Role of Irisin throughout Women's Life Span. Biomedicines. 2023;11(12):3260 Jalil Y, Gutierrez-Arias R et al. Myokine Secretion Dynamics and Their Role in Critically Ill Patients: A Scoping Review. J Clin Med. 2025;14(9):2892. Moonen H.P.F.X., Van Zanten A.R.H. Bioelectric impedance analysis for body composition measurement and other potential clinical applications in critical illness. Curr. Opin. Crit. Care. 2021;27:344–353. Cottereau G., Sztrymf B et al. Handgrip strength to predict extubation outcome: A prospective multicenter trial. Ann. Intensiv. Care. 2021;11:144 Åkerfeldt T, Larsson A et al. Postsurgical Acute Phase Reaction is Associated with Decreased Levels of Circulating Myostatin. Inflammation. 2015;38(4):1727–30 Additional Declarations No competing interests reported. Cite Share Download PDF Status: Under Review Version 1 posted Reviews received at journal 05 May, 2026 Reviews received at journal 04 May, 2026 Reviews received at journal 24 Apr, 2026 Reviews received at journal 15 Apr, 2026 Reviewers agreed at journal 15 Apr, 2026 Reviews received at journal 14 Apr, 2026 Reviewers agreed at journal 14 Apr, 2026 Reviewers agreed at journal 13 Apr, 2026 Reviewers agreed at journal 13 Apr, 2026 Reviewers agreed at journal 13 Apr, 2026 Reviewers agreed at journal 12 Apr, 2026 Reviewers invited by journal 04 Apr, 2026 Editor assigned by journal 06 Mar, 2026 Submission checks completed at journal 06 Mar, 2026 First submitted to journal 27 Feb, 2026 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-8991519","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":618470460,"identity":"c9712813-f5d8-4240-a39b-5bd639866256","order_by":0,"name":"Otakar Psenicka","email":"","orcid":"","institution":"General University Hospital in Prague","correspondingAuthor":false,"prefix":"","firstName":"Otakar","middleName":"","lastName":"Psenicka","suffix":""},{"id":618470461,"identity":"8a0f3fc4-dada-482c-b967-8ca0e48cf639","order_by":1,"name":"Tomas Brutvan","email":"","orcid":"","institution":"General University Hospital in Prague","correspondingAuthor":false,"prefix":"","firstName":"Tomas","middleName":"","lastName":"Brutvan","suffix":""},{"id":618470462,"identity":"38990756-9ff3-44de-a2ae-3d5eedb64c1e","order_by":2,"name":"Hana Vitkova","email":"","orcid":"","institution":"General University Hospital in Prague","correspondingAuthor":false,"prefix":"","firstName":"Hana","middleName":"","lastName":"Vitkova","suffix":""},{"id":618470463,"identity":"ad09bb95-187c-4e55-8478-5f3de8e3be18","order_by":3,"name":"Zuzana Krsakova","email":"","orcid":"","institution":"General University Hospital in Prague","correspondingAuthor":false,"prefix":"","firstName":"Zuzana","middleName":"","lastName":"Krsakova","suffix":""},{"id":618470464,"identity":"c22a56e7-1171-48c0-89f0-945be66d538e","order_by":4,"name":"Jan Kratky","email":"","orcid":"","institution":"General University Hospital in Prague","correspondingAuthor":false,"prefix":"","firstName":"Jan","middleName":"","lastName":"Kratky","suffix":""},{"id":618470465,"identity":"df7ce8b3-9b15-4cce-90a9-ba9bda2825d0","order_by":5,"name":"Jan Skrha Jr","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA0ElEQVRIie3RLQsCMRjA8WccnGVgXbuvsGH1w+z6uGIxTgQtivWSfgVFEOOGcGnXTb5gNWiRi27J+JxNcP+wtB/PXgBisR+M6LAakNAZGxh+R2glwbWfFQhTvB1JprUhjTsVXa1ezO4hyzR2sFkhE3ocDJipd8w6ECOUaMUTeMhc2/m295yATLCDkcWdk8aT1YHeuPUkRUnpb02PMl9XlFwCoTi58wN1Mt+4VHjCRIkRsVDi2lQyX55vF2MnffzFhA6/8olhMwAyfEssFov9fW8Am0erH0bamQAAAABJRU5ErkJggg==","orcid":"","institution":"General University Hospital in Prague","correspondingAuthor":true,"prefix":"","firstName":"Jan","middleName":"","lastName":"Skrha","suffix":"Jr"},{"id":618470466,"identity":"d29ce560-ade6-47b9-b38c-5caf8db3926c","order_by":6,"name":"Jarmila Krizova","email":"","orcid":"","institution":"General University Hospital in Prague","correspondingAuthor":false,"prefix":"","firstName":"Jarmila","middleName":"","lastName":"Krizova","suffix":""}],"badges":[],"createdAt":"2026-02-27 20:53:15","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-8991519/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-8991519/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":106835598,"identity":"6e305528-689a-47fc-ae41-f0167e70b052","added_by":"auto","created_at":"2026-04-14 02:01:37","extension":"jpg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":85086,"visible":true,"origin":"","legend":"\u003cp\u003eLength of hospital stay in patients with different myokines levels on day 0\u003c/p\u003e","description":"","filename":"1.jpg","url":"https://assets-eu.researchsquare.com/files/rs-8991519/v1/9de2e46cb0b8271f6ae166e3.jpg"},{"id":106960640,"identity":"a97d5917-d7e9-42f4-a269-17d19ff958ad","added_by":"auto","created_at":"2026-04-15 09:22:23","extension":"jpg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":98207,"visible":true,"origin":"","legend":"\u003cp\u003eDifference between mean myokine levels in the study group and the controls\u003c/p\u003e","description":"","filename":"2.jpg","url":"https://assets-eu.researchsquare.com/files/rs-8991519/v1/f91ce8c778ab6b11d0014405.jpg"},{"id":106835596,"identity":"f122f378-b193-457c-b781-a7f83d2a6717","added_by":"auto","created_at":"2026-04-14 02:01:37","extension":"jpg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":117322,"visible":true,"origin":"","legend":"\u003cp\u003eCorrelation of myokine levels with change in quadriceps muscle thickness\u003c/p\u003e","description":"","filename":"3.jpg","url":"https://assets-eu.researchsquare.com/files/rs-8991519/v1/88d2d8c19453d9599c10cda0.jpg"},{"id":106963094,"identity":"d73a56d1-e4f0-46f4-9c42-43b6d35ffb5f","added_by":"auto","created_at":"2026-04-15 09:42:06","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1020259,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-8991519/v1/0ed6c6d1-5fe6-488b-99f9-8d8a4ee71772.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Myostatin and irisin levels in predicting the outcome of patients with systemic inflammation: A prospective observational study","fulltext":[{"header":"Introduction","content":"\u003cp\u003eMuscle weakness develops in approximately half of critically ill patients (\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e). Among those with sepsis or systemic inflammatory response syndrome (SIRS) of other etiologies, its prevalence is even higher, up to 75% (\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e). The pathogenesis of intensive care unit-acquired weakness (ICU-AW) is multifactorial. General factors of critical illness, such as persistent catabolic processes, immobilization, mechanical ventilation etc., can contribute to the development of ICU-AW. On the other hand, complex alterations in muscle physiology and biochemistry occur at the molecular level. These include mitochondrial dysfunction, increased production of reactive oxygen species, impaired autophagy, and changes in membrane ion channel function (\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e). These processes accelerate muscle atrophy and reduce muscle function, leading to prolonged mechanical ventilation, difficult rehabilitation, longer hospital stays, and increased morbidity and mortality (\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e). Same mechanisms are also a key driver to long-term functional impairment persisting after discharge from intensive care, referred to as post-intensive care syndrome (PICS) (\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eSkeletal muscle itself may be involved in the complex pathogenesis of ICU-AW through the release of specific signalling molecules, so-called \u003cem\u003emyokines\u003c/em\u003e. These peptide- or protein-based cytokines have autocrine and paracrine effects on muscle fibres and surrounding structures (satellite cells, fascia, bone), while upon release into the circulation they also exert endocrine effects on distant tissues (\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e). The most extensively studied effects relate to glucose metabolism and adipose tissue regulation; current research also focuses on their impact on the brain and gastrointestinal tract (\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eAlthough several hundred myokines have been described to date, detailed information about their structure and function exist only for a few dozen. The first identified myokine was myostatin (\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e). Experimental models demonstrate that myostatin inhibits muscle protein synthesis, accelerates protein degradation, and suppresses both muscle growth and differentiation. Myostatin plasma levels are reduced after both aerobic and anaerobic exercise (\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e). Muscular animal models with myostatin deficiency have been described (\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e), as well as a case report of a human infant presenting with pronounced muscularity and a confirmed homozygous mutation in the myostatin gene (\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e). Myostatin inhibitors have been considered as promising therapeutic candidates for the treatment of sarcopenia and genetic muscular dystrophies, supported by encouraging results from animal studies. In humans, however, no molecule has yet demonstrated a significant clinical benefit (\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e). Clinical studies in humans have further reported inconsistent findings regarding circulating myostatin levels across different disease states. (\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e, \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e) For instance, Amor et al. (\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e) reported elevated circulating myostatin levels in obesity, correlating with insulin resistance and suggesting a role in chronic metabolic dysfunction. In contrast, Wirtz et al. (\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e) observed that low myostatin serum levels in critically ill patients were associated with poor outcomes, indicating that acute systemic inflammation and severe illness may alter myostatin regulation differently than chronic disease states.\u003c/p\u003e \u003cp\u003eIrisin is an exercise-induced myokine that influences muscle hypertrophy, regulation of thermogenesis, and the browning of white adipose tissue (\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e). Its circulating levels correlate with various clinical parameters in obese individuals and patients with type 2 diabetes (\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e). Yet other studies have shown inconsistent and sometimes contradictory findings, particularly regarding its relationship with muscle mass and muscle strength. While lower irisin levels have been reported in obesity and type 2 diabetes, suggesting an association with metabolic dysfunction (\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e), studies in older adults and postmenopausal women have demonstrated variable associations between circulating irisin, muscle mass, and functional measures of muscle strength. In older adults with sarcopenia, lower irisin concentrations have been observed compared with healthy controls (\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e), while another study reported an inverse correlation between irisin levels, CT-assessed thigh muscle thickness, and hand-grip strength (\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eMuscle dysfunction in patients with systemic inflammation can be objectively assessed using electromyography (EMG) (\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e). However, due to its invasive nature, EMG is rarely used in this indication. Instead, non-invasive methods such as hand-grip strength or more complex MRC (Medical Research Council) score are more commonly applied in day-to-day practise (\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e). Functional performance assessments, including the six-minute walking test, the Timed Up \u0026amp; Go test or the Short Physical Performance Battery can be performed on cooperating patients (\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eMuscle mass assessment with dual-energy X-ray absorptiometry DXA, computed tomography CT or magnetic resonance imaging MRI are dominantly used in research studies and are not routinely investigated in clinical setting (\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e). In recent years, bedside ultrasound of skeletal muscles has gained increasing use in the ICU due to its routine availability, non-invasiveness and good reproducibility. (\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e). Quadriceps muscle thickness (QMT) is the most commonly measured parameter. This assessment can be performed repeatedly during the course of illness to evaluate the degree of muscle loss and/or change in muscle quality. The decline of muscle thickness correlates with ICU-AW and with poor clinical outcomes (\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThe aim of our study was to examine potential associations between circulating levels of selected myokines (myostatin, irisin) and outcomes in patients with systemic inflammatory states. We hypothesized that patients with higher myostatin and/or lower irisin concentrations at disease onset would experience worse outcomes, with the primary endpoint being length of hospital stay. Secondary analyses focused on correlations between myokine levels and additional parameters (laboratory and anthropometric parameters, muscle strength), as well as the potential role of bedside ultrasound of the thigh muscle in assessing catabolism and predicting outcomes. To date, most clinical investigations of selected myokines have been limited to animal models or highly specific patient groups. Prospective observational studies exploring the impact of myokines on hospital stay and functional outcomes in patients with systemic inflammation are to the best of our knowledge not yet available in the literature.\u003c/p\u003e"},{"header":"Methodology","content":"\u003cp\u003eThis was a single-centre prospective observational pilot study. All patients admitted with an acute illness to the 3rd Department of Internal Medicine or the Department of Anaesthesiology, Resuscitation and Intensive Medicine at the General University Hospital in Prague were considered for enrolment. Eligible patients met the criteria for a systemic inflammatory response syndrome (SIRS), defined as the presence of at least two of the following: body temperature\u0026thinsp;\u0026gt;\u0026thinsp;38\u0026deg;C or \u0026lt;\u0026thinsp;36\u0026deg;C, heart rate\u0026thinsp;\u0026gt;\u0026thinsp;90 bpm, respiratory rate\u0026thinsp;\u0026gt;\u0026thinsp;20/min or PaCO₂ \u0026lt;4.3 kPa, leukocytosis\u0026thinsp;\u0026gt;\u0026thinsp;12 \u0026times; 10\u003csup\u003e6\u003c/sup\u003e/l, or leukopenia\u0026thinsp;\u0026lt;\u0026thinsp;4 \u0026times; 10\u003csup\u003e6\u003c/sup\u003e/l. A minimum expected hospital stay of five days was required for enrolment. \u003cem\u003e(Note: SIRS criteria were used to enable inclusion of patients with non-septic conditions, such as acute pancreatitis.)\u003c/em\u003e Exclusion criteria included transfer from another hospital with a prior length of stay exceeding 48 hours, terminal illness (malignant or non-malignant), and pre-admission long-term immobility. Written informed consent was obtained from all participants. In cases where participants were temporarily unable to provide written consent due to their clinical condition, informed consent was obtained verbally or through affirmative non-verbal communication in the presence of a witness. For these participants, written informed consent was obtained as soon as their clinical condition allowed. Ethical approval was provided by the General University Hospital in Prague Ethics Commission, ID 38/23, 20/04/2023. The control group consisted of healthy individuals matched with age and sex where applicable. Controls were defined as individuals free of acute or chronic illnesses that could confound study outcomes. All controls underwent screening consisting of medical history and physical examination. Individuals were excluded for any autoimmune, inflammatory, cardiovascular, metabolic, or other systemic disease requiring treatment. Written informed consent was obtained from all controls.\u003c/p\u003e \u003cp\u003eA total of 30 patients in a study group and 24 controls were included in the study from March 2023 to December 2024. Sample size was determined prior to study initiation based on feasibility considerations and expert statistician consultation. No formal a priori power calculation based on predefined effect sizes was performed. The primary outcome was length of hospital stay, defined as the number of days from hospital admission to discharge alive. Six patients died during the follow-up period and were therefore excluded from the analysis of the primary outcome, as length of hospital stay is not a defined or interpretable endpoint in non-survivors. In deceased patients, secondary outcomes and the composite outcome were analysed. Secondary outcomes included associations between baseline circulating myokine levels and 1) laboratory markers of inflammation and nutritional status; 2) anthropometric parameters and bioimpedance analysis; 3) handgrip strength; 4) ultrasound-derived measures of thigh muscle mass, as well as the prognostic value of these measures for clinical outcomes. Secondary outcomes were considered exploratory and hypothesis-generating. Also, the composite outcome (BAD) was defined a priori for exploratory purposes as a hospital length of stay (LoS) above the 75th percentile, or an ICU length of stay (LoS-ICU) above the 75th percentile, or transfer to a long-term care facility, or death.\u003c/p\u003e \u003cp\u003eImmediately after enrolment, and no later than within 48 hours, blood samples were collected from participants in both the study and control groups to determine myostatin (MSTN ELISA Kit, Cat. No: MBS021687) and irisin (Human Irisin ELISA Kit, Cat. No: MBS706887) levels. Myokines were measured in paired serum samples, and the mean value of two measured concentrations was used for analysis. In the study group also laboratory markers of inflammation (CRP, procalcitonin, neutrophile to lymphocyte ratio NLR) and nutritional status (albumin, prealbumin) were assessed. Anthropometric parameters, muscle measurements and bioimpedance analysis (body weight, BMI, body fat percentage, lean body mass, handgrip strength, ultrasound-derived measures) were assessed in both study and control groups. Handgrip strength was evaluated using a portable dynamometer (Trailite TL-LSC 100), and quadriceps muscle thickness was measured by ultrasound UGEO HM70A (Samsung, Seoul, Korea.)\u003c/p\u003e \u003cp\u003eIn the study group, the same assessment was repeated on day 10 after admission.\u003c/p\u003e \u003cp\u003eUltrasound measurements were conducted with linear transducer (3\u0026ndash;16 MHz) in musculoskeletal pre-set. The quadriceps femoris muscle of the dominant lower limb was used for the investigation. All measurements were conducted by the same investigator (OP) according to a predetermined protocol. Patients were lying supine with extended knees and toes pointing to the ceiling. As the exact point for the measurement, the one-third of the distance from cranial patella margin to anterior inferior iliac spine on the pelvis was determined [25]. Three measurements of total thickness of the muscle (i.e. rectus femoris and vastus intermedius (RF\u0026thinsp;+\u0026thinsp;VI)) were obtained and the average value was calculated and recorded.\u003c/p\u003e \u003cp\u003eAll statistical analyses were performed using STATISTICA version 12 (Statsoft Inc., Tulsa, OK, USA). Continuous variables were first tested for normality using the Shapiro\u0026ndash;Wilk test. Homogeneity of variances between groups was assessed using Levene\u0026rsquo;s test. Normally distributed variables with equal variances were compared using the independent samples \u003cem\u003et\u003c/em\u003e-test. For non-normally distributed variables or in the presence of unequal variances, the Mann\u0026ndash;Whitney \u003cem\u003eU\u003c/em\u003e test was applied. Correlations between continuous variables were evaluated using Pearson\u0026rsquo;s correlation coefficient for normally distributed data or Spearman\u0026rsquo;s rank correlation coefficient for non-normally distributed data. Paired t-tests were used for within-group comparisons over time. All statistical tests were two-tailed, and a \u003cem\u003ep\u003c/em\u003e-value\u0026thinsp;\u0026lt;\u0026thinsp;0.05 was considered statistically significant. Given the exploratory nature of the secondary outcomes, no formal correction for multiple testing was applied. Data are expressed as mean\u0026thinsp;\u0026plusmn;\u0026thinsp;standard deviation (SD) unless otherwise stated.\u003c/p\u003e \u003cp\u003e The study protocol was approved by the Ethics Committee of General University Hospital in Prague.\u003c/p\u003e"},{"header":"Results","content":"\u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003eStudy Group and Control Group\u003c/h2\u003e \u003cp\u003e \u003cdiv class=\"BlockQuote\"\u003e \u003cp\u003eThe study group included 30 participants (mean age 67.9 years, range 24\u0026ndash;89 years; 50% males) with mean weight 82.04 kg (\u0026plusmn;\u0026thinsp;18.34) and mean BMI 27.43 (\u0026plusmn;\u0026thinsp;5.59). The control group consisted of 24 participants (mean age of 35.9 years, range 27\u0026ndash;54, 50% males). Mean weight was 75.86 kg (\u0026plusmn;\u0026thinsp;10.92) and BMI was 23.98 (\u0026plusmn;\u0026thinsp;2.47).\u003c/p\u003e \u003c/div\u003e \u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003eLaboratory values and muscle parameters\u003c/h3\u003e\n\u003cp\u003eTable\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e presents baseline muscle and laboratory data of the study group and the control group. Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e presents the development of values in the study group on day 10.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eBaseline characteristics of the study group and the control group.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"3\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\"\u0026plusmn;\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003e\u003cb\u003eHandgrip (kg)\u003c/b\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eStudy group\u003c/p\u003e \u003cp\u003e- Baseline\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eControl group\u003c/p\u003e \u003cp\u003e- Baseline\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003e20.7 (\u0026plusmn;\u0026thinsp;9.89)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003e39.51 (\u0026plusmn;\u0026thinsp;8.80)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eUS RF\u0026thinsp;+\u0026thinsp;VI (mm)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e25.80 (\u0026plusmn;\u0026thinsp;5.83)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e36.34 (\u0026plusmn;\u0026thinsp;8.05)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eFat mass (%)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e34.2 (\u0026plusmn;\u0026thinsp;9.65)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e23.47 (\u0026plusmn;\u0026thinsp;7.67)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eLTM (kg\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e41.25 (\u0026plusmn;\u0026thinsp;10.59)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e51.48 (\u0026plusmn;\u0026thinsp;10.63)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eCreatinine (umol/l)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e151.63 (\u0026plusmn;\u0026thinsp;129.57)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eCRP (mg/l)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e271.47 (\u0026plusmn;\u0026thinsp;129.11)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003ePCT (ug/l)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e23.67 (\u0026plusmn;\u0026thinsp;41.09)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eAlbumin (g/l)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e29.72 (\u0026plusmn;\u0026thinsp;5.77)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eNLR\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e18.64 (\u0026plusmn;\u0026thinsp;11.96)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eMyostatin (ng/ml)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e29.04 (\u0026plusmn;\u0026thinsp;13.25)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e11.86 (\u0026plusmn;\u0026thinsp;9.12)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eIrisin (ng/ml)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e41.80 (\u0026plusmn;\u0026thinsp;57.26)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e33,70 (\u0026plusmn;\u0026thinsp;30.65)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eDevelopment of measured values in the study group on day 10\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"3\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\"\u0026plusmn;\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\"\u0026plusmn;\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003e\u003cb\u003eHandgrip (kg)\u003c/b\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eStudy group\u003c/p\u003e \u003cp\u003e- Baseline\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eStudy group\u003c/p\u003e \u003cp\u003e- Day 10\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003e20.7 (\u0026plusmn;\u0026thinsp;9.89)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003e21.9 (\u0026plusmn;\u0026thinsp;8.68)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eUS QMT (mm)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e25.80 (\u0026plusmn;\u0026thinsp;5.83)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e23.33 (\u0026plusmn;\u0026thinsp;6.24)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eFat mass (%)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e34.2 (\u0026plusmn;\u0026thinsp;9.65)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e41 (\u0026plusmn;\u0026thinsp;14.18)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eLBM (kg)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e41.25 (\u0026plusmn;\u0026thinsp;10.59)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e40.61 (\u0026plusmn;\u0026thinsp;11.08)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eCreatinine (umol/l)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e151.63 (\u0026plusmn;\u0026thinsp;129.57)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e122.52 (\u0026plusmn;\u0026thinsp;139.37)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eCRP (mg/l)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e271.47 (\u0026plusmn;\u0026thinsp;129.11)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e76.3 (\u0026plusmn;\u0026thinsp;72.95)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003ePCT (ug/l)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e23.67 (\u0026plusmn;\u0026thinsp;41.09)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e0.44 (\u0026plusmn;\u0026thinsp;0.25)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eAlbumin (g/l)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e29.72 (\u0026plusmn;\u0026thinsp;5.77)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e27.52 (\u0026plusmn;\u0026thinsp;4.51)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eNLR\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e18.64 (\u0026plusmn;\u0026thinsp;11.96)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e5.74 (\u0026plusmn;\u0026thinsp;3.09)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eMyostatin (ng/ml)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e29.04 (\u0026plusmn;\u0026thinsp;13.25)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e16.54 (\u0026plusmn;\u0026thinsp;10.47)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eIrisin (ng/ml)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e41.80 (\u0026plusmn;\u0026thinsp;57.26)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e81.72 (\u0026plusmn;\u0026thinsp;61.73)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e\n\u003ch3\u003eMyostatin and Irisin analysis\u003c/h3\u003e\n\u003cp\u003eThe median myostatin concentration in the study cohort was 29.04 \u0026micro;g/mL, and the median irisin concentration was 41.80 \u0026micro;g/mL. Participants with myostatin levels below the median (n\u0026thinsp;=\u0026thinsp;11) had a mean hospital stay of 25.73 days (\u0026plusmn;\u0026thinsp;21.04), those with higher myostatin levels (n\u0026thinsp;=\u0026thinsp;13) had a mean hospital stay of 21.97 days (\u0026plusmn;\u0026thinsp;20.81). Patients with lower irisin levels (n\u0026thinsp;=\u0026thinsp;10) had a mean hospital stay of 21.60 days (\u0026plusmn;\u0026thinsp;19.86), compared with 25.50 days (\u0026plusmn;\u0026thinsp;21.86) in those with higher irisin concentrations (n\u0026thinsp;=\u0026thinsp;14), (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). No significant differences were found between the two subgroups (p\u0026thinsp;=\u0026thinsp;0.59 and p\u0026thinsp;=\u0026thinsp;0.659 respectively.) Similarly, length of ICU stay was analysed with no significant differences found between groups with lower and higher myostatin or irisin (p\u0026thinsp;=\u0026thinsp;0.76 and p\u0026thinsp;=\u0026thinsp;0.62 respectively.)\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eIn the control group, mean myostatin and irisin levels were 11.86 \u0026micro;g/mL and 33.70 \u0026micro;g/mL, which were significantly lower than in the study cohort (p\u0026thinsp;=\u0026thinsp;\u0026lt;\u0026thinsp;0.001 and p\u0026thinsp;=\u0026thinsp;0.015 respectively), (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e.)\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eSignificantly higher irisin levels were observed in women compared with men, both among patients (89.03 vs. 43.91 \u0026micro;g/mL; \u003cem\u003ep\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.028) and controls (52.304 vs. 15.1 \u0026micro;g/mL; \u003cem\u003ep\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.001). No sex-related differences were found in myostatin concentrations.\u003c/p\u003e\n\u003ch3\u003eSecondary analysis\u003c/h3\u003e\n\u003cp\u003eAs part of the secondary analyses, correlations were observed between irisin and BMI and LTM (p\u0026thinsp;=\u0026thinsp;0.001 and p\u0026thinsp;=\u0026thinsp;0.001 respectively), between myostatin and CRP (p\u0026thinsp;=\u0026thinsp;0.001), and between myostatin and NLR (p\u0026thinsp;=\u0026thinsp;0.021). Furthermore, both myokines correlated with the change in thigh muscle thickness assessed by ultrasound: myostatin showed a positive correlation (p\u0026thinsp;=\u0026thinsp;0.008), whereas irisin showed a negative correlation (p\u0026thinsp;=\u0026thinsp;0.019) (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e). Ultrasound-measured thigh muscle thickness was positively correlated with lean body mass (p\u0026thinsp;=\u0026thinsp;0.002), and handgrip strength measured by dynamometry (p\u0026thinsp;=\u0026thinsp;0.002).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e"},{"header":"Discussion","content":"\u003cp\u003eTo the best of our knowledge, none of the studies published to date have investigated the association between myostatin and irisin, muscle dysfunction and subsequent outcomes in critically ill patients with such a comprehensive scope of assessed parameters as in our study. This multimodal approach to the development of muscle weakness and its impact on functional outcomes represents the main strength of the presented study.\u003c/p\u003e \u003cp\u003eBy introducing a control group, we found that the levels of both investigated myokines were significantly lower in the control group compared to the study group. This finding is consistent with previously published data in patients with chronic kidney disease [26], liver cirrhosis [27], and COPD [28], where elevated myostatin levels have been associated with worse prognosis. However, previous studies in critically ill patients have reported contradictory findings. For example, Wirtz et al. [14] reported higher mortality and morbidity in patients with lower myostatin levels. Our analysis also suggested a possible association between lower myostatin levels and worse composite outcome (due to the wide confidence interval and low statistical power of the study, this result should be interpreted with caution and confirmed in larger cohorts). Taken together, available evidence suggests that the prognostic significance of circulating myostatin is highly context dependent. While chronically elevated myostatin appears to contribute to muscle wasting and adverse outcomes in chronic diseases, low myostatin levels in acute critical illness may reflect exhausted myokine production and reduced muscle reserve [29].\u003c/p\u003e \u003cp\u003eDespite the relatively small sample size, a significant difference in irisin levels between sexes was observed, with higher concentrations in women than in men, both in the study cohort and in the control group. Higher irisin levels in women have been demonstrated in previous studies [30]. The exact underlying mechanism remains unclear but circulating estradiol levels and sex-related differences in the distribution of brown and white adipose tissue are likely contributing factors [31].\u003c/p\u003e \u003cp\u003eRapid skeletal muscle loss within just a few days of systemic inflammation is a well-described phenomenon [4]. In our cohort, lean body mass decreased by 1,2 kg over a ten-day period, accompanied by an average reduction in ultrasound-measured quadriceps muscle thickness of 0,8 millimetres. A notable finding is the demonstrated correlation of both myokines with this change in quadriceps thickness. Our results indicate that lower baseline myostatin and higher baseline irisin were associated with less pronounced muscle loss over time. However, these associations should be interpreted as descriptive rather than casual. As highlighted by a recent scoping review [32], the relationships between myokines and muscle loss may vary in critically ill patients, especially depending on patient\u0026rsquo;s mobility and performed physical intervention.\u003c/p\u003e \u003cp\u003eWhen relying on a single method to monitor muscle loss, the results may be unreliable. Both ultrasound muscle assessment and bioimpedance can be affected by systemic oedema [33]. Handgrip strength measurement demonstrates lower reliability in patients with reduced muscle strength and is often limited by poor cooperation in critically ill individuals [34]. In our cohort, we observed correlations between the different measurement modalities, however, methodological limitations of handgrip strength and bioimpedance may have influenced some associations. Nevertheless, ultrasound assessment of quadriceps muscle thickness appears to be a valuable tool for monitoring temporal changes, given its simplicity, bedside feasibility, and the routine availability of ultrasound devices in intensive care units.\u003c/p\u003e \u003cp\u003eThis study has several limitations. One is a relatively small sample size. A preliminary sample size was estimated (based on available data of myokine concentrations and average length of hospital stay in Czech Republic), but our data suggests, that even with much larger number of probands, the results would still be insignificant. Length of hospital stay is also not an ideal primary outcome, due to potential influence from other factors, e.g. availability of aftercare beds. Also, exclusion of patients who died during hospitalization from the primary outcome may have introduced survivor bias. There was also a substantial age difference between patients and controls. Given this age difference, between-group comparisons should be interpreted rather descriptively than as evidence of disease-specific effects.\u003c/p\u003e \u003cp\u003eDespite given inclusion and exclusion criteria, residual confounding and heterogeneity of included patients related to age, comorbidities, disease severity and unmeasured metabolic or inflammatory factors could not be excluded. Significantly different levels of myostatin and irisin in healthy controls indicate that these factors could influence baseline myokine concentrations and thus the subsequent results. Some of the previously published studies demonstrated relatively rapid changes in myostatin levels during the post-insult period and their correlation with inflammatory parameters [35]. Therefore, the allowed time window of 48 from admission may also be a small limitation, as the exact timing of sample collection in relation to the onset and duration of the primary insult could therefore be crucial.\u003c/p\u003e \u003cp\u003eA mild limitation of our study is also the methodology used for the ultrasound assessment of the thigh muscle. Ultrasound measurements were performed at two-thirds of the distance between the anterior inferior iliac spine and the superior border of the patella. Although this site may increase sensitivity for detecting peripheral muscle atrophy, it is less frequently used in previous literature compared with the mid-thigh position. As a result, direct comparison of absolute thickness values with other studies should be interpreted with caution.\u003c/p\u003e"},{"header":"Conclusions","content":"\u003cp\u003eThe present paper reports data from a pilot observational study. The selected myokines, myostatin and irisin, were not associated with the primary outcome\u0026mdash;length of hospital stay. Exploratory secondary analysis suggests that these myokines may reflect aspects of muscle metabolism within a multimodal approach to the management of critically ill patients. Ultrasound assessment of the thigh muscle appears to be a useful and easily applicable method for monitoring dynamic changes in muscle thickness and, potentially, muscle quality.\u003c/p\u003e"},{"header":"Abbreviations","content":"\u003cdiv class=\"DefinitionList\"\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003e\u003cb\u003eBMI\u003c/b\u003e\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eBody mass index\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003e\u003cb\u003eCRP\u003c/b\u003e\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eC\u0026ndash;reactive protein\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003e\u003cb\u003eDXA\u003c/b\u003e\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003edual\u0026ndash;energy X\u0026ndash;ray absorptiometry\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003e\u003cb\u003eEMG\u003c/b\u003e\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eelectromyography\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003e\u003cb\u003eHGS\u003c/b\u003e\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003ehand grip strength\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003e\u003cb\u003eICU\u003c/b\u003e\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003e \u003cb\u003eAW\u003c/b\u003e\u0026ndash;intensive care unit\u0026ndash;acquired weakness\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003e\u003cb\u003eLBM\u003c/b\u003e\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eLean body mass\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003e\u003cb\u003eLoS\u003c/b\u003e\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003elength of hospital stay\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003e\u003cb\u003eMRC\u003c/b\u003e\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003emedical research council\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003e\u003cb\u003eNLR\u003c/b\u003e\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eneutrophile to leukocyte ratio\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003e\u003cb\u003ePCT\u003c/b\u003e\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eprocalcitonin\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003e\u003cb\u003ePICS\u003c/b\u003e\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003epost\u0026ndash;intensive care syndrome\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003e\u003cb\u003eSIRS\u003c/b\u003e\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003esystemic inflammatory response syndrome\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003e\u003cb\u003eUS QMT\u003c/b\u003e\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eultrasound measured thickness of quadriceps muscle\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003c/div\u003e"},{"header":"Declarations","content":"\u003cp\u003e \u003ch2\u003eClinical trial number\u003c/h2\u003e \u003cp\u003e \u003cem\u003eThe study was not prospectively registered. Retrospective registration at ClinicalTrials.gov is currently in progress. The registration number will be added to the manuscript as soon as it becomes available\u003c/em\u003e.\u003c/p\u003e \u003c/p\u003e\u003cp\u003e \u003ch2\u003eEthics approval and consent to participate:\u003c/h2\u003e \u003cp\u003e The study was conducted in accordance with the Declaration of Helsinki and approved by the Ethics Committee of General University Hospital in Prague, ID 38/23(approval date: 20 April 2023). Informed consent was obtained from all subjects involved in the study.\u003c/p\u003e \u003c/p\u003e \u003cp\u003e \u003cstrong\u003eCompeting interests:\u003c/strong\u003e \u003cp\u003eThe authors declare no competing interests.\u003c/p\u003e \u003c/p\u003e\u003ch2\u003eFunding:\u003c/h2\u003e \u003cp\u003eThis research and the APC was funded by MH CZ\u0026mdash;DRO (General University Hospital in Prague\u0026mdash;VFN), grant number 00064165.\u003c/p\u003e\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eConceptualization, O.P., T.B., Z.K., J.K. (Jan Kratky), J.S. and J.K. (Jarmila Krizova); methodology, O.P., J.S. and J.K. (Jarmila Krizova), software, O.P. and J.K. (Jarmila Krizova); formal analysis, O.P. and J.K. (Jarmila Krizova); investigation, O.P, T.B., Z.K., J.K. (Jan Kratky), J.S. and J.K. (Jarmila Krizova), resources, O.P., T.B., Z.K., J.K. (Jan Kratky), J.S. and J.K. (Jarmila Krizova); data curation, O.P., T.B., Z.K., J.K. (Jan Kratky), J.S. and J.K. (Jarmila Krizova); writing\u0026mdash;original draft preparation, O.P. and J.K. (Jarmila Krizova); writing\u0026mdash;review and editing, O.P., J.S. and J.K. (Jarmila Krizova); visualization, O.P. and J.K. (Jarmila Krizova); supervision, J.K. (Jarmila Krizova); project administration O.P., J.S. and J.K. (Jarmila Krizova); funding acquisition, O.P., J.S. and J.K. (Jarmila Krizova). All authors have read and agreed to the published version of the manuscript.\u003c/p\u003e\u003ch2\u003eData Availability\u003c/h2\u003e\u003cp\u003eThe datasets used and/or analysed during the current study are available from the corresponding author upon reasonable request.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eSchefold JC, Weber-Carstens S et al. Muscular weakness and muscle wasting in the critically ill. J Cachexia Sarcopenia Muscle. 2020;11(6):1399\u0026ndash;1412.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eCallahan LA, Supinski GS. Sepsis-induced myopathy. Crit Care Med. 2009;37(10 Suppl):S354-67\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eVanhorebeek I, Latronico N, Van den Berghe G. ICU-acquired weakness. Intensive Care Med. 2020;46(4):637\u0026ndash;653\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003ePuthucheary Z.A., Sidhu P.S. et al. Acute Skeletal Muscle Wasting in Critical Illness. JAMA. 2013;310:1591\u0026ndash;1600\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eNeedham DM, Davidson J, Cohen H et al. Improving long-term outcomes after discharge from intensive care unit: report from a stakeholders' conference. Crit Care Med. 2012; 40(2): 502\u0026ndash;9.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003ePedersen BK, Febbraio MA. Muscles, exercise and obesity: skeletal muscle as a secretory organ. Nat Rev Endocrinol. 2012;8(8):457\u0026ndash;65\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBlume GR, Royes LFF. Peripheral to brain and hippocampus crosstalk induced by exercise mediates cognitive and structural hippocampal adaptations. Life Sci. 2024;352:122799\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMcPherron AC, Lawler AM, Lee SJ. Regulation of skeletal muscle mass in mice by a new TGF-beta superfamily member. Nature. 1997;387(6628):83\u0026ndash;90\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eHittel DS, Kraus WE et al. Myostatin decreases with aerobic exercise and associates with insulin resistance. Med Sci Sports Exerc. 2010;42(11):2023\u0026ndash;9\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eKobayashi M, Kaneki M et al. Myostatin deficiency not only prevents muscle wasting but also improves survival in septic mice. Am J Physiol Endocrinol Metab. 2021;320(1):E150-E159.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSchuelke M, Lee SJ et al. Myostatin mutation associated with gross muscle hypertrophy in a child. N Engl J Med. 2004;350(26):2682\u0026ndash;8.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMariot V, Dumonceaux J et al. Downregulation of myostatin pathway in neuromuscular diseases may explain challenges of anti-myostatin therapeutic approaches. Nat Commun. 2017;8(1):1859.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eAmor M, Stulnig TM et al. Serum Myostatin is Upregulated in Obesity and Correlates with Insulin Resistance in Humans. Exp Clin Endocrinol Diabetes. 2019;127(8):550\u0026ndash;556.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWirtz TH, Koch A et al. Low Myostatin Serum Levels Are Associated with Poor Outcome in Critically Ill Patients. Diagnostics (Basel). 2020;10(8):574.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWaseem R, Islam A et al. FNDC5/Irisin: Physiology and Pathophysiology. Molecules. 2022;27(3):1118.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eShoukry A, Khalifa A et al. Circulating serum irisin levels in obesity and type 2 diabetes mellitus. IUBMB Life. 2016;68(7):544\u0026ndash;56\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eChang JS, Kong ID et al. Circulating irisin levels as a predictive biomarker for sarcopenia: A cross-sectional community-based study. Geriatr Gerontol Int. 2017;17(11):2266\u0026ndash;2273\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003ePark, HS., Kim, H.C., Zhang, D. et al. The novel myokine irisin: clinical implications and potential role as a biomarker for sarcopenia in postmenopausal women. \u003cem\u003eEndocrine\u003c/em\u003e 64, 341\u0026ndash;348 (2019).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eHermans G, Van den Berghe G. Clinical review: intensive care unit acquired weakness. Crit Care. 2015;19(1):274\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWu TT, Li H. Effects of a multilevel intervention of resistance training with or without beta-hydroxy-beta-methylbutyrate in medical ICU patients during entire hospitalisation: a four-arm multicentre randomised controlled trial. Crit Care. 2023;27(1):493.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003evan der Steen-Dieperink MJMM, Koekkoek WAC, Kouw IWK. Sarcopenia and frailty in critical illness. Curr Opin Clin Nutr Metab Care. 2025;28(3):192\u0026ndash;199.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLooijaard W.G., Molinger J., Weijs P.J. Measuring and monitoring lean body mass in critical illness. Curr. Opin. Crit. Care. 2018;24:241\u0026ndash;247\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eZhang Y, Ma F et al. Development and validation of machine learning-based risk prediction models for ICU-acquired weakness: a prospective cohort study. Eur J Med Res. 2025;30(1):666. doi: \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1186/s40001-025-02930-8\u003c/span\u003e\u003cspan address=\"10.1186/s40001-025-02930-8\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e. Erratum in: Eur J Med Res. 2025;30(1):1158.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBone RC, Sibbald WJ et al. Definitions for sepsis and organ failure and guidelines for the use of innovative therapies in sepsis. The ACCP/SCCM Consensus Conference Committee. American College of Chest Physicians/Society of Critical Care Medicine. Chest. 1992;101(6):1644-55.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMart\u0026iacute;n C.A.G., Zepeda E.M., M\u0026eacute;ndez O.A.L. Bedside Ultrasound Measurement of Rectus Femoris: A Tutorial for the Nutrition Support Clinician. J. Nutr. Metab. 2017;2017:2767232\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eVerzola D, Garibotto G et al. Apoptosis and myostatin mRNA are upregulated in the skeletal muscle of patients with chronic kidney disease. Kidney Int. 2011;79(7):773\u0026ndash;82.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eNishikawa H, Nishiguchi S et al. Elevated serum myostatin level is associated with worse survival in patients with liver cirrhosis. J Cachexia Sarcopenia Muscle. 2017;8(6):915\u0026ndash;925.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eJu CR, Chen RC. Serum myostatin levels and skeletal muscle wasting in chronic obstructive pulmonary disease. Respir Med. 2012;106(1):102\u0026ndash;8.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSharma S, Patil AS. Myostatin's marvels: From muscle regulator to diverse implications in health and disease. Cell Biochem Funct. 2024;42(6):e4106\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eZ\u0026uuml;gel M, Schumann U et al. The role of sex, adiposity, and gonadectomy in the regulation of irisin secretion. Endocrine. 2016;54(1):101\u0026ndash;110.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBarbagallo F, Calogero AE et al. The Role of Irisin throughout Women's Life Span. Biomedicines. 2023;11(12):3260\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eJalil Y, Gutierrez-Arias R et al. Myokine Secretion Dynamics and Their Role in Critically Ill Patients: A Scoping Review. J Clin Med. 2025;14(9):2892.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMoonen H.P.F.X., Van Zanten A.R.H. Bioelectric impedance analysis for body composition measurement and other potential clinical applications in critical illness. Curr. Opin. Crit. Care. 2021;27:344\u0026ndash;353.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eCottereau G., Sztrymf B et al. Handgrip strength to predict extubation outcome: A prospective multicenter trial. Ann. Intensiv. Care. 2021;11:144\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003e\u0026Aring;kerfeldt T, Larsson A et al. Postsurgical Acute Phase Reaction is Associated with Decreased Levels of Circulating Myostatin. Inflammation. 2015;38(4):1727\u0026ndash;30\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"european-journal-of-medical-research","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"ejmr","sideBox":"Learn more about [European Journal of Medical Research](http://eurjmedres.biomedcentral.com)","snPcode":"40001","submissionUrl":"https://submission.nature.com/new-submission/40001/3","title":"European Journal of Medical Research","twitterHandle":"@BioMedCentral","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"BMC/SO AJ","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"myokines, critical illness, systemic inflammation, muscle ultrasound","lastPublishedDoi":"10.21203/rs.3.rs-8991519/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-8991519/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003e \u003cb\u003eBackground\u003c/b\u003e:\u003c/p\u003e \u003cp\u003eSystemic inflammatory response syndrome (SIRS) is associated with changes in muscle metabolism. Resulting muscle weakness is linked with adverse outcomes, e.g. prolonged mechanical ventilation, length of hospital stay and increased mortality. Skeletal muscles produce myokines, which may contribute to the development of muscle weakness. The aim of this study was to assess the potential utility of selected myokine levels in predicting the prognosis of patients with SIRS.\u003c/p\u003e \u003cp\u003e \u003cb\u003eMethods\u003c/b\u003e:\u003c/p\u003e \u003cp\u003eThis was a prospective observational study. Levels of myostatin and irisin, selected anthropometric, laboratory and muscle parameters (ultrasound measured thickness of quadriceps muscle US QMT, hand grip strength HGS, lean body mass LBM) were recorded within 48h from admission and at the day 10 of hospital stay. Control group consisted of healthy individuals.\u003c/p\u003e \u003cp\u003e \u003cb\u003eResults\u003c/b\u003e:\u003c/p\u003e \u003cp\u003eA total of 54 participants (30 in the study group and 24 controls) were included in the study. Primary outcome (LoS=length of hospital stay) was not significantly different in probands with higher or lower myostatin or irisin levels (p\u0026thinsp;=\u0026thinsp;0.59 and p\u0026thinsp;=\u0026thinsp;0.659). Myostatin and irisin levels in control group were significantly lower than in study cohort (11.86 \u0026micro;g/L vs. 29.04 \u0026micro;g/mL, p\u0026thinsp;=\u0026thinsp;\u0026lt;\u0026thinsp;0.001 and 33.70 \u0026micro;g/L vs. 41.80 ug/L, p\u0026thinsp;=\u0026thinsp;0.015). Irisin levels were higher in women than in men both in probands (p\u0026thinsp;=\u0026thinsp;0.028) and controls (p\u0026thinsp;=\u0026thinsp;0.001). There was a significant correlation between myostatin and CRP and NLR (p\u0026thinsp;=\u0026thinsp;0.001; p\u0026thinsp;=\u0026thinsp;0.021) and between irisin and BMI (p\u0026thinsp;=\u0026thinsp;0.001). Both myostatin (p\u0026thinsp;=\u0026thinsp;0.008) and irisin (p\u0026thinsp;=\u0026thinsp;0.019) levels were associated with change of US QMT. QMT correlated with LBM (p\u0026thinsp;=\u0026thinsp;0.002) and HGS (p\u0026thinsp;=\u0026thinsp;0.002).\u003c/p\u003e \u003cp\u003e \u003cb\u003eConclusions\u003c/b\u003e:\u003c/p\u003e \u003cp\u003eThere was no significant association of myokine levels with LoS. A significant correlation between baseline myokines levels and US QMT change was present which suggest their potential role in muscle metabolism in critically ill patients. US QMT may be a useful method to monitor muscle wasting.\u003c/p\u003e","manuscriptTitle":"Myostatin and irisin levels in predicting the outcome of patients with systemic inflammation: A prospective observational study","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-04-14 02:01:33","doi":"10.21203/rs.3.rs-8991519/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"editorInvitedReview","content":"","date":"2026-05-06T00:55:04+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-05-04T05:17:22+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-04-24T07:31:37+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-04-15T07:52:18+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"285591322410149615955920418364396997325","date":"2026-04-15T06:08:06+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-04-14T14:01:09+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"174440973015621075047815643069832369343","date":"2026-04-14T13:32:29+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"310499138851065112553924331246851934764","date":"2026-04-14T03:31:15+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"326565324211113262710994788213497053832","date":"2026-04-13T14:01:17+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"114640231062330072250117446458479296144","date":"2026-04-13T04:27:14+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"195827615379695393509957938463222936913","date":"2026-04-13T03:58:42+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2026-04-04T18:12:25+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2026-03-06T07:49:17+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2026-03-06T07:44:50+00:00","index":"","fulltext":""},{"type":"submitted","content":"European Journal of Medical Research","date":"2026-02-27T20:43:22+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"european-journal-of-medical-research","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"ejmr","sideBox":"Learn more about [European Journal of Medical Research](http://eurjmedres.biomedcentral.com)","snPcode":"40001","submissionUrl":"https://submission.nature.com/new-submission/40001/3","title":"European Journal of Medical Research","twitterHandle":"@BioMedCentral","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"BMC/SO AJ","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"16b30b6b-916b-4f13-927a-2e7e97d5935b","owner":[],"postedDate":"April 14th, 2026","published":true,"recentEditorialEvents":[{"type":"editorInvitedReview","content":"","date":"2026-05-06T00:55:04+00:00","index":51,"fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-05-04T05:17:22+00:00","index":50,"fulltext":""}],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2026-04-14T02:01:34+00:00","versionOfRecord":[],"versionCreatedAt":"2026-04-14 02:01:33","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-8991519","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-8991519","identity":"rs-8991519","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}