Plantar intrinsic foot muscle activity and its relationship with postural sway during single-legged and bipedal tiptoe standing in ballet dancers

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Thus, the activity of the plantar intrinsic foot muscles (PIFMs), which stabilize the foot joints, may be important in reducing postural sway during tiptoe standing. We compared PIFM activity during single-legged and bipedal tiptoe standing and examined its relationship to postural sway in dancers. In 11 female ballet dancers, the electromyography (EMG) amplitudes of PIFMs and the center of pressure (COP) data were recorded during single-legged and bipedal tiptoe standing tasks. The EMG amplitudes were normalized to those during the maximal voluntary contraction, and PIFM activity level and its coefficient of variation over time (EMG-CVtime) during the task were assessed. From the COP data, standard deviations in the anteroposterior (COP-SDAP) and mediolateral (COP-SDML) direction, velocity, and area were calculated. PIFM activity level and COP velocity were 2–2.5-fold higher in the single-legged than bipedal task (p≤0.003). Significant correlations were found between PIFM activity level and COP velocity (r=0.666, p=0.025) and between EMG-CVtime and COP-SDAP or COP-SDML (r≥0.738, p≤0.010) only in the single-legged task. These results suggest that PIFM activity is associated with postural sway, especially during single-legged tiptoe standing in dancers. Biological sciences/Neuroscience Health sciences/Anatomy high-density electromyography temporal variability postural sway center of pressure foot Figures Figure 1 Figure 2 Figure 3 Figure 4 Introduction Reducing postural sway during tiptoe standing ("demi-pointe" in ballet terminology) is essential for ballet dancers (hereafter referred to as "dancers") 1 , 2 . In particular, single-legged tiptoe standing (STS) is frequently employed in ballet choreography because the unsupported leg can be used for a variety of expression. During STS, dancers are required to maintain a high and stable foot arch structure in the supported leg, which is aesthetically desirable 3 , 4 . The foot arch structure is primarily supported by passive and non-contractile components (e.g., bones, ligaments, plantar fascia, etc.) 5 . However, in situations of high postural demands or heavy foot loading, stabilization of the foot arch structure is achieved by additional muscle-generated forces 6 , 7 . Given that the foot joints of dancers are characterized by hypermobility 8 , 9 , the activity of the muscles involved in the stability of these joints may be important in reducing postural sway during STS. The plantar intrinsic foot muscles (PIFMs), which originate and insert within the foot, function in the stability or mobility of the foot joints 5 , 6 , 10 – 12 . Electromyography (EMG) studies in non-dancers have shown that PIFM activity increases or decreases in response to postural demands or foot loading; PIFM activity level is significantly higher in single-legged standing, bipedal tiptoe standing (BTS), and STS compared to bipedal standing 6 , 13 . Recent studies also suggest that the primary role of PIFMs during standing is to stabilize the foot joint (i.e., indirectly contribute to postural control) due to their short moment arms 5 , 14 , 15 . Nevertheless, there is little information on how PIFMs activity is associated with postural sway during tiptoe standing performed by dancers. Our previous study showed that dancers had much less postural sway and lower level/variability of PIFM activity during BTS, compared to non-dancers 16 . This suggests that BTS is not a high postural demand for dancers and that low and steady PIFM activity is associated with less postural sway. However, no studies have examined PIFM activity during STS and how it relates to postural sway in dancers. The tiptoe standing that dancers perform in daily practice and on stage requires a large ankle plantar flexion (PF) angle, which is not achievable in non-dancers, and this is even more so during STS 8 , 9 , 16 . When comparing muscle activity between individuals/conditions and examining its relationship to other parameters such as postural sway, a well-controlled task setting with the specified/same joint angle is appropriate 17 , 18 . In fact, our previous study found that PIFM activity and postural sway during BTS differed among different ankle PF angles, and the relationships between these variables were also different depending on the ankle PF angle 16 . Thus, comparing PIFM activity between STS and BTS, as well as examining its relationship with postural sway, at a large and specified ankle PF angle will shed light on dancers’ postural control during tiptoe standing. However, this has never been studied. Some previous studies have used intramuscular EMG to examine PIFM activity 6 , 7 , 13 , but there are difficulties in using this technique due to its invasive nature, especially considering its potential detrimental effect on the dancers' subsequent performance. This study therefore adopted high-density EMG using a grid with multiple surface electrodes, which can noninvasively record PIFM activity across a large region of the plantar foot 14 , 16 , 19 . The objectives of this study were to 1) compare PIFM activity and postural sway between STS and BTS conditions in dancers, and 2) examine the relationship between PIFM activity and postural sway in each condition. We hypothesized that 1) PIFM activity (its level and temporal variability) and postural sway would be significantly higher during STS than during BTS, and 2) PIFM activity would be associated with postural sway during both STS and BTS but especially the former. Methods Participants Eleven female ballet dancers (age: 25.1 ± 2.3 y, height: 163.9 ± 6.3 cm, body mass: 47.9 ± 4.9 kg, BMI: 17.8 ± 1.2 kg/m 2 ) were enrolled in this study. The participants were the same as those in our recent publication 16 , which compared postural sway and PIFM activity during BTS in dancers versus non-dancers (n = 14 vs 13). This study reports original data for STS that was performed by eleven dancers only, while deriving the data from our previous study for BTS performed by the same eleven dancers. Dancers needed to have an at least 10 years of ballet experience and still receive at least 7.5 hours of ballet training per week. None of the participants had a history of injury or surgery in the ankle and foot joints within the past 3 months or 1 year, respectively. The study protocols complied with the principles of the Declaration of Helsinki and were approved by the Ethics Committee of Ritsumeikan University (BKC-LSMH-2021-048), and all participants provided written informed consent. Experimental Protocol The postural control task consisted of BTS for 30 seconds and STS (right leg) for 10 seconds, both at ankle PF 60° 16 , 20 . Electric goniometers (SG110, Biometrics, UK) were applied to measure ankle PF angles during the postural control tasks. The stationary arm of the goniometer was aligned with the long axis of the fibula in the sagittal plane, while the moving arm was aligned with the plantar plane on the side of the little toe (i.e., fifth metatarsal bone) and attached to both feet. Note that the ankle PF angle is the sum of the talocrural joint and several foot joints (Chopart’s joint, Lisfranc’s joint, etc.). The visual feedback of the goniometer data of each foot was provided in real time via two 16-bit A/D converters (PowerLab 2/20; ADInstruments, Australia) and on two PC monitors located at participants’ eye level, approximately 1 m in front of them (Fig. 1 A) 16 , 20 . During the STS task, the goniometer on the left (unsupported) leg was removed. Participants initially stood on a force plate (SS-FP40AO-SY, Sports Sensing, Japan). In the BTS task, they began tiptoe standing while holding the bar in front of themselves with their hands, and then removed their hands from the bar after they were able to maintain the PF angles of both feet at the specified angle as much as possible by watching the monitor so that the body mass on both feet was equal. During the BTS task, they kept both feet parallel at a comfortable stance width, with the knees fully extended, and hands relaxed on the sides of the body. In the STS task, participants started the right leg tiptoe standing with both hands holding the bar, and when they were able to maintain the PF angle at the specified angle as much as possible while watching the monitor, they removed their hands from the bar. During the STS task, the right leg was maintained in optimal turnout (i.e., external rotation of the lower limb), the left leg in retiré (i.e., the left small toe on the knee joint of the right leg), and the upper limb in en avant (i.e., the upper limbs in a circular position with both fingertips in front of the trunk) (Fig. 1 B). Considering the degree of postural demand, trials were performed in the order of the BTS task and then STS task. Participants performed practice trials to familiarize themselves with the procedure and subsequently performed 3 trials at each task with a rest period of at least 1 minute between trails. The average data from three successful trials were used in the data analysis. A successful trial was defined as one in which the participant was able to maintain the specified angle without grasping the bar or stepping out during the trial. Data Acquisition Monopolar surface EMG amplitudes from the PIFMs were acquired with a high-density grid of 64 channels (GR08MM1305, OT Bioelettronica, Italy) consisting of 13 rows and 5 columns (minus one electrode) with an 8 mm inter-electrode distance in both directions (Fig. 2 A), in accordance with prior studies 14 , 16 , 19 . The right plantar skin was lightly rubbed with sandpaper and cleaned with alcohol. After palpation of the heel and metatarsal fat pads, a high-density grid was placed in the center of these areas, aligned with the long axis of the foot (i.e., second metatarsal) (Fig. 2 B) 14 , 16 , 19 . The grid was reinforced with tapes to ensure consistent contact with the sole at any ankle PF angle during the tasks. Reference electrodes were placed around the right knee and left wrist. The acquired amplitudes were amplified using a 16-bit analog-to-digital converter (Quattrocento; OT Bioelectronica, Italy), with a sampling frequency of 2048 Hz and a bandpass filter of 10–500 Hz (Fig. 2 C). During the tasks, the COP data were acquired using the force plate and a 16-bit A/D converter (PowerLab/16SP; ADInstruments, Australia) with a sampling frequency of 1000 Hz and a low-pass filter of 5 Hz. Additionally, participants performed 5-s maximum voluntary contractions (MVCs) against manual resistance provided by one researcher twice for each of toe flexion (all toes) and toe abduction (the great and little toes), during which EMG were recorded 13 , 16 , 21 . Data Analysis The EMG amplitude and COP data were synchronized using a trigger from a 16-bit A/D converter (PowerLab/8SP; ADInstruments, Australia). The analysis interval was 20 s excluding the first 5 s from the start of the task in the BTS task and 5 s excluding the first 2.5 s from the start of the task in the ST task. EMG signals recorded from 64 electrodes were visually inspected, and channels showing noise were reconstructed based on the interpolation of the signals from neighboring channels 14 , 16 , 19 . For each channel, the EMG root-mean-square (RMS) values during the tasks were calculated and normalized to the highest value over a 500-ms time window during the MVC tasks. The normalized EMG values were averaged across 64-channels 14 , 16 , 19 , and used as a criterion value for PIFM activity level (% MVC). From the EMG amplitude, the coefficient of variation over time (EMG-CV time ) during the tasks was also calculated to evaluate the temporal variability of PIFM activity level. This was calculated by dividing the standard deviation (SD) by the mean of the EMG amplitudes during the analysis interval for each channel and then averaging over all 64 channels 16 , 22 , 23 . From the COP data, the SD in the anteroposterior and mediolateral directions (COP-SD AP and COP-SD ML ), average velocity (COP-Velocity), and area of a 95% confidence ellipse encompassing the COP (COP-Area) were further calculated for the analysis interval as indices of postural sway 16 , 24 , 25 . Statistical Analysis For all variables, the Shapiro-Wilk test was applied to assess normality, which was confirmed for all variables except for PIFM activity level and EMG-CV time in the BTS task, and COP-Area in the STS task. Therefore, between-task comparisons were made by Wilcoxon's signed rank test for these non-normally distributed variables, and by paired t-tests for the other variables. Effect sizes of between-task differences were calculated as Cohen’s d values and were interpreted as trivial < 0.2; small 0.2–0.49; moderate 0.5–0.79; and large ≥ 0.8 26 . Additionally, their bootstrap 95% confidence interval (5,000 samples, bias-corrected and accelerated) was assessed by using estimation statistics to improve statistical inference 27 . To evaluate the relationship between COP variables and EMG variables in each task, Pearson's correlation coefficient and Spearman's rank correlation coefficient were calculated for normally and non-normally distributed data, respectively. Values were considered statistically significant at p < 0.05. All data were analyzed using SPSS software (SPSS Statistics 28, IBM, USA) unless otherwise stated. Results Compared to the BTS task, the STS task had significantly higher COP-Velocity (BTS vs STS, 2.0 ± 0.3 vs 5.1 ± 0.4 cm/s, p < 0.001, d = 8.77, Fig. 3 C) and PIFM activity level (11.4 ± 2.8 vs 25.8 ± 7.8%MVC, p = 0.003, d = 2.47, Fig. 4 A). There was no significant difference between tasks in the other variables (p = 0.093–0.941, d = 0.05–0.61, Figs. 3 and 4 ). In the STS task, significant correlations were found between PIFM activity level and COP-Velocity (r = 0.666, p = 0.025), between EMG-CV time and COP-SD AP (r = 0.846, p = 0.001), and between EMG-CV time and COP-SD ML (r = 0.738, p = 0.010) (Table 1 ). In the BTS task, no correlation was found between any combinations of the variables (r = 0.097–0.559, p = 0.074–0.778, Table 1 ). Table 1 Correlation coefficients between COP and EMG variables PIFM activity level (%MVC) EMG-CV time (%) COP Position r P r p SD AP (cm) BTS 0.174 0.608 0.097 0.778 STS 0.083 0.808 0.846 ** 0.001 SD ML (cm) BTS −0.210 0.536 0.340 0.306 STS −0.037 0.913 0.738 ** 0.010 Velocity (cm/s) BTS 0.282 0.400 0.559 0.074 STS 0.666 * 0.025 0.499 0.118 Area (cm 2 ) BTS 0.000 1.000 0.362 0.275 STS −0.191 0.574 0.301 0.368 Significance of Pearson’s correlation coefficient and Spearman's rank correlation coefficient are indicated as follows: *p < 0.05, **p < 0.01. COP, center of pressure; SD, standard deviation; AP, anteroposterior; ML, mediolateral; PIFM, plantar intrinsic foot muscle; EMG-CV time , temporal variability of EMG; BTS, bipedal tiptoe standing; STS, single-legged tiptoe standing. Discussion The main findings of this study are as follows: 1) COP-Velocity and PIFM activity level were higher in the STS than BTS task, and 2) significant correlations were found between COP and EMG variables only in the STS task. These results partially support our hypothesis and suggest that foot loading and postural demands are increased during STS compared to BTS, and that PIFM activity is particularly associated with postural sway during STS in dancers. In the present study, only COP-Velocity of the four COP variables was significantly higher in the STS than BTS task by 2.6-fold on average. This was consistent for all dancers, as shown by the individual plots in Fig. 3 C. COP-Velocity represents the average distance traveled by the COP per second, regardless of the directions, and a higher value is interpreted as greater postural sway 24 , 25 . Postural stability is primarily biomechanically constrained by three conditions where: 1) the base of support is wide, 2) the line of gravity is in the center of the base of support, and 3) the center of gravity is low 28 , 29 . Compared to BTS, STS is particularly disadvantaged in conditions 1 and 2, resulting in generally higher postural demands. The results of this study suggest that this is no exception for dancers accustomed to STS. In contrast, the other three COP variables did not significantly differ between tasks. This is apparently due to inconsistent responses/patterns among dancers during STS compared to BTS, and these inter-individual variabilities suggest that there are large individual differences in their postural control strategies during the tiptoe standing tasks. More specifically, some dancers were higher but others were lower during STS than BTS in COP-SD AP (Fig. 3 A), COP-SD ML (Fig. 3 B), and COP-Area (Fig. 3 D), which are all influenced by the directions and degree of variability of the COP trajectory. Overall, these results suggest that COP-Velocity can serve as a representative variable for postural sway, and the other variables can supplement directional information, in studies adopting tiptoe standing in dancers. PIFM activity level (% MVC) in the STS task was significantly higher than in the BTS task by 2.2-fold on average, and this was also consistent for all dancers (Fig. 4 A). Since the body mass load on the foot is simply twice as heavy with the single-legged compared to bipedal support, it makes sense to assume that most of this increase in PIFM activity level is due to the increased foot loading. Furthermore, the correlation analysis showed that PIFM activity level was positively correlated with COP-Velocity (r = 0.666) only in the STS task, indicating that activity level was indeed associated with postural sway particularly during STS. A study examining PIFM activity level in non-dancers reported that it was 1.5 to 1.7-fold higher in STS compared to BTS 13 . However, the tasks in that study were not compared robustly because the participants (all participants during STS and half during BTS) lightly touched a wall or other objects during postural control, and the ankle joint PF angle was not specified 13 . Taken together, the results of this study suggest that PIFM activity, particularly during STS, is dependent on foot loading and postural demands, ensuring the methodological validity of the present study that matched the PF angle during both tasks. Contrary to our expectations, EMG-CV time did not significantly differ between tasks (p = 0.142), although STS on average had a 1.2-fold higher value with a borderline small/moderate effect size (d = 0.49) (Fig. 4 B). Higher and lower values of EMG-CV time reflect greater neuromuscular fluctuation and greater steadiness 22 , 23 , respectively, and therefore we expected it to be higher for STS than BTS. However, it is worth mentioning that our previous study 16 also found no significant differences in EMG-CV time during BTS performed at 20°, 40°, and 60° in dancers, while PIFM activity level was significantly higher for 60° than 20°, which is in line with the EMG findings of this study (i.e. different activity level, similar steadiness). In other words, these results suggest that in dancers, although PIFM activity is higher during STS than BTS, its activity is similarly steady during both STS and BTS at their respective levels. This is likely due to adaptations to dancers’ daily training where they perform STS as steady as possible. Also, EMG-CV time showed a strong positive correlation with COP-SD AP and COP-SD ML only in the STS task (r = 0.846 and 0.738, Table 1 ). These suggest that PIFM activity is associated with postural sway in both directions during STS in dancers, and that these indices representing the variability of the EMG and directional COP data are sensitive to each other in the STS condition. A previous study has shown that PIFM activity during single-legged standing (with the heel on the floor) in non-dancers is synchronized with COP sway only in the mediolateral direction 6 . The reason for this discrepancy may be partly attributed to the participants being dancers vs non-dancers, but may also be explained by the combined motion of foot joints and the function of windlass mechanism due to the difference in the limb position. The foot joints have a flexibly shape-changing structure 5 , 30 , and in single-legged standing, each joint responds in a coordinated manner to postural sway, primarily in the frontal plane (i.e., mediolateral direction). For example, eversion of the subtalar joint in the hindfoot causes the combined motion such as inversion of the Chopart's and Lisfranc's joint in the mid/forefoot (and vice versa), resulting in a lowering/collapse of the medial longitudinal arch 12 , 31 , 32 . In tiptoe standing, on the other hand, the plantar fascia covering the calcaneus to the toes is tensed as the metatarsophalangeal joint is extended, resulting in the windlass mechanism that raises the medial longitudinal arch and increases joint stiffness of the foot; when this mechanism functions, the joints of the foot are unified, thus the aforementioned combined motion is reduced 33 . The present findings support recent suggestions that PIFMs are more actively involved in the windlass mechanism than previously considered 10 , 34 – 36 , and add that their less variable (i.e., steadier) activity is associated with less postural sway during STS in dancers. Limitations This study had a relatively small sample size (n = 11), due to difficulty in recruiting professional/high-level dancers, potentially reducing statistical power. For example, our previous study 16 with a larger sample size (n = 14) found that EMG-CV time was found to be positively correlated with COP-Velocity in the BTS task, which was not the case in either task in this study. Furthermore, both tasks in this study were compared only at the ankle PF joint angle of 60°, and it is unknown whether the results are generalizable to other PF joint angles. Further investigations addressing these issues are needed in the light of both kinetics and kinematic mechanics to better understand postural control of dancers. Conclusion In summary, PIFM activity level and postural sway were higher during single-legged than bipedal tiptoe standing in dancers, likely due to increased foot loading and postural demands. The findings of the correlations between EMG and COP variables provide new evidence that PIFM activity is associated with postural sway during tiptoe standing in dancers, especially performed on a single leg. Declarations Author Contribution H.F. and S.M.: Investigation, Resources, Writing original drafts. Y.K. and T.I.: Formal analysis, Visualization, Formal analysis. Data curation. Data Availability The datasets used and/or analysed during the current study are available from the corresponding author on reasonable request. References Costa MS da S, Ferreira A de S, Felicio LR. Equilíbrio estático e dinâmico em bailarinos: revisão da literatura. Fisioterapia e Pesquisa . 2013;20(3):299-305. doi:10.1590/S1809-29502013000300016 de Mello MC, de Sá Ferreira A, Ramiro Felicio L. Postural Control During Different Unipodal Positions in Professional Ballet Dancers. J Dance Med Sci . 2017;21(4):151-155. doi:10.12678/1089-313X.21.4.151 Salzano A, Camuso F, Sepe M, Sellami M, Ardigò LP, Padulo J. Acute effect of toe cap choice on toe deviation angle and perceived pain in female professional ballet dancers. Biomed Res Int . 2019;2019. doi:10.1155/2019/9515079 Kadel N, Boenisch M, Teitz C, Trepman E. Stability of Lisfranc joints in ballet pointe position. Foot Ankle Int . 2005;26(5):394-400. doi:10.1177/107110070502600510 McKeon PO, Hertel J, Bramble D, Davis I. The foot core system: a new paradigm for understanding intrinsic foot muscle function. Br J Sports Med . 2015;49(5):290. doi:10.1136/bjsports-2013-092690 Kelly LA, Kuitunen S, Racinais S, Cresswell AG. Recruitment of the plantar intrinsic foot muscles with increasing postural demand. Clinical Biomechanics . 2012;27(1):46-51. doi:10.1016/j.clinbiomech.2011.07.013 Kurihara T, Rowley M, Reischl S, Baker L, Kulig K. Effect of a task’s postural demands on medial longitudinal arch deformation and activation of foot intrinsic and extrinsic musculature. Acta Bioeng Biomech . 2020;22(4):1-15. doi:10.37190/ABB-01623-2020-02 Russell JA, Shave RM, Kruse DW, Koutedakis Y, Wyon MA. Ankle and foot contributions to extreme plantar- and dorsiflexion in female ballet dancers. Foot Ankle Int . 2011;32(2):183-188. doi:10.3113/FAI.2011.0183 Russell JA, Kruse DW, Koutedakis Y, Mcewan IM, Wyon MA. Pathoanatomy of Posterior Ankle Impingement in Ballet Dancers. Clinical Anatomy . 2010;23(6):613-621. doi:10.1002/ca.20991 Farris DJ, Birch J, Kelly L. Foot stiffening during the push-off phase of human walking is linked to active muscle contraction, and not the windlass mechanism. J R Soc Interface . 2020;17(168). doi:10.1098/rsif.2020.0208 Kelly LA, Lichtwark G, Cresswell AG. Active regulation of longitudinal arch compression and recoil during walking and running. J R Soc Interface . 2015;12(102). doi:10.1098/rsif.2014.1076 Fiolkowski P, Brunt D, Bishop M, Woo R, Horodyski M. Intrinsic pedal musculature support of the medial longitudinal arch: An electromyography study. Journal of Foot and Ankle Surgery . 2003;42(6):327-333. doi:10.1053/j.jfas.2003.10.003 Ridge ST, Rowley KM, Kurihara T, et al. Contributions of Intrinsic and Extrinsic Foot Muscles during Functional Standing Postures. Biomed Res Int . 2022;2022. doi:10.1155/2022/7708077 Ferrari E, Cooper G, Reeves ND, Hodson-Tole EF. Intrinsic foot muscles act to stabilise the foot when greater fluctuations in centre of pressure movement result from increased postural balance challenge. Gait Posture . 2020;79:229-233. doi:10.1016/j.gaitpost.2020.03.011 Zhang X, Schütte KH, Vanwanseele B. Foot muscle morphology is related to center of pressure sway and control mechanisms during single-leg standing. Gait Posture . 2017;57:52-56. doi:10.1016/j.gaitpost.2017.05.027 Fukuyama H, Maeo S, Kusagawa Y, Ono M, Watanabe K, Isaka T. Plantar intrinsic foot muscle activity and its relationship with postural sway during tiptoe standing in ballet dancers and non-dancers. Gait Posture . 2024;108:139-144. doi:10.1016/j.gaitpost.2023.11.023 Vieira TM, Botter A. The Accurate Assessment of Muscle Excitation Requires the Detection of Multiple Surface Electromyograms. Exerc Sport Sci Rev . 2021;49(1):23-34. doi:10.1249/JES.0000000000000240 Watanabe K, Vieira TM, Gallina A, Kouzaki M, Moritani T. Novel Insights into Biarticular Muscle Actions Gained from High-Density Electromyogram. Exerc Sport Sci Rev . 2021;49(3):179-187. doi:10.1249/JES.0000000000000254 Ferrari E, Cooper G, Reeves ND, Hodson-Tole EF. Surface electromyography can quantify temporal and spatial patterns of activation of intrinsic human foot muscles. Journal of Electromyography and Kinesiology . 2018;39:149-155. doi:10.1016/j.jelekin.2018.02.009 Saito S, Obata H, Kuno-Mizumura M, Nakazawa K. On the skilled plantar flexor motor action and unique electromyographic activity of ballet dancers. Exp Brain Res . 2018;236(2):355-364. doi:10.1007/s00221-017-5131-0 F. P. Kendall, K. McCreary, P. G. Provance. Muscle: Testing and Function with Posture and Pain . 5th edition.; 2005. Lemos T, Imbiriba LA, Vargas CD, Vieira TM. Modulation of tibialis anterior muscle activity changes with upright stance width. Journal of Electromyography and Kinesiology . 2015;25(1):168-174. doi:10.1016/j.jelekin.2014.07.009 Kurz E, Faude O, Roth R, Zahner L, Donath L. Ankle muscle activity modulation during single-leg stance differs between children, young adults and seniors. Eur J Appl Physiol . 2018;118(2):239-247. doi:10.1007/s00421-017-3764-0 Moghadam M, Ashayeri H, Salavati M, et al. Reliability of center of pressure measures of postural stability in healthy older adults: Effects of postural task difficulty and cognitive load. Gait Posture . 2011;33(4):651-655. doi:10.1016/j.gaitpost.2011.02.016 Palmieri RM, Ingersoll CD, Stone MB, Krause BA. Center-of-Pressure Parameters Used in the Assessment of Postural Control. J Sport Rehabil . 2002;11(1):51-66. doi:10.1123/jsr.11.1.51 Cohen J. Statistical Power Analysis for the Behavioral Sciences . Routledge; 2013. doi:10.4324/9780203771587 Ho J, Tumkaya T, Aryal S, Choi H, Claridge-Chang A. Moving beyond P values: data analysis with estimation graphics. Nat Methods . 2019;16(7):565-566. doi:10.1038/s41592-019-0470-3 Nashner LM, McCollum G. The organization of human postural movements: A formal basis and experimental synthesis. Behavioral and Brain Sciences . 1985;8(1):135-150. doi:10.1017/S0140525X00020008 Horak FB. Postural orientation and equilibrium: what do we need to know about neural control of balance to prevent falls? Age Ageing . 2006;35(suppl_2):ii7-ii11. doi:10.1093/ageing/afl077 Neumann DA. Kinesiology of the Musculoskeletal System: Foundations of Rehabilitation.3rd Ed. .; 2017. Razeghi M, Batt ME. Foot type classification: a critical review of current methods. Gait Posture . 2002;15(3):282-291. doi:10.1016/S0966-6362(01)00151-5 Mulligan EP, Cook PG. Effect of plantar intrinsic muscle training on medial longitudinal arch morphology and dynamic function. Man Ther . 2013;18(5):425-430. doi:10.1016/j.math.2013.02.007 Hicks JH. The mechanics of the foot. II. The plantar aponeurosis and the arch. J Anat . 1954;88(1):25-30. Welte L, Kelly LA, Lichtwark GA, Rainbow MJ. Influence of the windlass mechanism on arch-spring mechanics during dynamic foot arch deformation. J R Soc Interface . 2018;15(145):20180270. doi:10.1098/rsif.2018.0270 Kelly LA, Farris DJ, Cresswell AG, Lichtwark GA. Intrinsic foot muscles contribute to elastic energy storage and return in the human foot. J Appl Physiol . 2019;126:231-238. doi:10.1152/japplphysiol.00736.2018.-The Riddick R, Farris DJ, Kelly LA. The foot is more than a spring: Human foot muscles perform work to adapt to the energetic requirements of locomotion. J R Soc Interface . 2019;16(150). doi:10.1098/rsif.2018.0680 Additional Declarations No competing interests reported. Cite Share Download PDF Status: Published Journal Publication published 23 May, 2025 Read the published version in Scientific Reports → Version 1 posted Editorial decision: Revision requested 20 Apr, 2025 Reviews received at journal 19 Apr, 2025 Reviewers agreed at journal 25 Mar, 2025 Reviews received at journal 20 Oct, 2024 Reviewers agreed at journal 14 Oct, 2024 Reviewers agreed at journal 13 Oct, 2024 Reviewers invited by journal 12 Oct, 2024 Editor assigned by journal 08 Oct, 2024 Editor invited by journal 10 Jul, 2024 Submission checks completed at journal 10 Jul, 2024 First submitted to journal 08 Jul, 2024 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. 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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-4702997","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":334268060,"identity":"d4ebbe11-4ce4-400a-9a86-d8f8467b8c89","order_by":0,"name":"Hiroshi Fukuyama","email":"data:image/png;base64,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","orcid":"","institution":"Ritsumeikan University","correspondingAuthor":true,"prefix":"","firstName":"Hiroshi","middleName":"","lastName":"Fukuyama","suffix":""},{"id":334268061,"identity":"2b7a07d1-bb5c-41ac-aeef-11050039a92c","order_by":1,"name":"Sumiaki Maeo","email":"","orcid":"","institution":"Ritsumeikan University","correspondingAuthor":false,"prefix":"","firstName":"Sumiaki","middleName":"","lastName":"Maeo","suffix":""},{"id":334268062,"identity":"540ec5a4-23e2-4ffd-b93e-b2beb7d0f968","order_by":2,"name":"Yuki Kusagawa","email":"","orcid":"","institution":"Ritsumeikan University","correspondingAuthor":false,"prefix":"","firstName":"Yuki","middleName":"","lastName":"Kusagawa","suffix":""},{"id":334268063,"identity":"d044347e-2e8f-43bc-9753-effeaf95bef2","order_by":3,"name":"Tadao Isaka","email":"","orcid":"","institution":"Ritsumeikan University","correspondingAuthor":false,"prefix":"","firstName":"Tadao","middleName":"","lastName":"Isaka","suffix":""}],"badges":[],"createdAt":"2024-07-08 06:13:00","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-4702997/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-4702997/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1038/s41598-025-02917-9","type":"published","date":"2025-05-23T15:58:40+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":61626419,"identity":"d56c10a5-a744-48fa-9d92-192b8b407e34","added_by":"auto","created_at":"2024-08-02 06:54:51","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":65303,"visible":true,"origin":"","legend":"\u003cp\u003eThe experimental setup. A: During bipedal tiptoe standing, the ankle plantar flexion angles of both feet, measured using goniometers, were shown as real time visual feedback on two PC monitors. B: During single-legged tiptoe standing, the right leg was maintained in optimal turnout (i.e., external rotation of the lower limb, the left leg in retiré (i.e., left small toe on the knee joint of the right leg), and the upper limb in en avant (i.e., upper limb in a circular position with both fingertips in front of the trunk). The feedback of ankle plantar flexion angle during single-legged was only for the right leg.\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-4702997/v1/642270d9c9026aa91a8e7539.png"},{"id":61626418,"identity":"9d23abb7-509e-4a45-a09f-f7f316a642ae","added_by":"auto","created_at":"2024-08-02 06:54:51","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":126769,"visible":true,"origin":"","legend":"\u003cp\u003eHigh-density grid and its application position on the foot. A: The high-density grid comprising 13 rows and 5 columns, with 8 mm distance between electrodes (except for one electrode at the apical corner on the little toe side); B: The grid was placed between the metatarsal head and heel adipose pads on the plantar surface. The foot image was created using “BodyParts3D, © The Database Center for Life Science licensed under CC Attribution-Share Alike 2.1 Japan.; C: Color maps showing representative high-density EMG amplitudes in the single-legged tiptoe stranding (STS) and bipedal tiptoe standing (BTS). The point near the center of the color map (cross mark) indicates the barycenter of electromyographic activity.\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-4702997/v1/9be92740b60f4ad109b36701.png"},{"id":61626416,"identity":"3fa7e118-6925-45e4-8af5-542bfce1a813","added_by":"auto","created_at":"2024-08-02 06:54:50","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":59057,"visible":true,"origin":"","legend":"\u003cp\u003eComparisons of COP variables (A: COP-SD\u003csub\u003eAP\u003c/sub\u003e, B: COP-SD\u003csub\u003eML\u003c/sub\u003e, C: COP-Velocity, D: COP-Area) between bipedal tiptoe standing (BTS) and single-leg tiptoe standing (STS). On the right axes, paired Cohen’s d values are plotted as boot strap sampling distributions. Mean Cohen’s d values are depicted as dots with horizontal lines; 95% confidence intervals are indicated by the ends of the vertical error bars. Significant differences between groups are indicated as **p \u0026lt; 0.01. COP, center of pressure; SD, standard deviation; AP, anteroposterior; ML, mediolateral.\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-4702997/v1/26a3d916f4ab49c5f3ee0d9c.png"},{"id":61626417,"identity":"13d4e41f-cf07-4089-9fb9-d8c0a2beebe5","added_by":"auto","created_at":"2024-08-02 06:54:50","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":31183,"visible":true,"origin":"","legend":"\u003cp\u003eComparisons of EMG variables (A: PIFM activity level, B: EMG-CV\u003csub\u003etime\u003c/sub\u003e) between bipedal tiptoe standing (BTS) and single-legged tiptoe standing (STS). On the right axes, paired Cohen’s d values are plotted as boot strap sampling distributions. Mean Cohen’s d values are depicted as dots with horizontal dashed lines; 95% confidence intervals are indicated by the ends of the vertical error bars. Significant differences between groups are indicated as **p \u0026lt; 0.01. PIFM, plantar intrinsic foot muscle; EMG-CV\u003csub\u003etime\u003c/sub\u003e, temporal variability of EMG.\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-4702997/v1/596b787b4c7b361e097dfa12.png"},{"id":83460153,"identity":"2ec6681b-810b-4a05-9de6-d04563e0a166","added_by":"auto","created_at":"2025-05-26 16:11:15","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":803484,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-4702997/v1/19069408-a4f2-4b6a-80a6-86834df76714.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Plantar intrinsic foot muscle activity and its relationship with postural sway during single-legged and bipedal tiptoe standing in ballet dancers","fulltext":[{"header":"Introduction","content":"\u003cp\u003eReducing postural sway during tiptoe standing (\"demi-pointe\" in ballet terminology) is essential for ballet dancers (hereafter referred to as \"dancers\")\u003csup\u003e\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e,\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u003c/sup\u003e. In particular, single-legged tiptoe standing (STS) is frequently employed in ballet choreography because the unsupported leg can be used for a variety of expression. During STS, dancers are required to maintain a high and stable foot arch structure in the supported leg, which is aesthetically desirable\u003csup\u003e\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e,\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e\u003c/sup\u003e. The foot arch structure is primarily supported by passive and non-contractile components (e.g., bones, ligaments, plantar fascia, etc.)\u003csup\u003e\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e\u003c/sup\u003e. However, in situations of high postural demands or heavy foot loading, stabilization of the foot arch structure is achieved by additional muscle-generated forces\u003csup\u003e\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e,\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e\u003c/sup\u003e. Given that the foot joints of dancers are characterized by hypermobility\u003csup\u003e\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e,\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e\u003c/sup\u003e, the activity of the muscles involved in the stability of these joints may be important in reducing postural sway during STS.\u003c/p\u003e \u003cp\u003eThe plantar intrinsic foot muscles (PIFMs), which originate and insert within the foot, function in the stability or mobility of the foot joints\u003csup\u003e\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e,\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e,\u003cspan additionalcitationids=\"CR11\" citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e\u003c/sup\u003e. Electromyography (EMG) studies in non-dancers have shown that PIFM activity increases or decreases in response to postural demands or foot loading; PIFM activity level is significantly higher in single-legged standing, bipedal tiptoe standing (BTS), and STS compared to bipedal standing\u003csup\u003e\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e,\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e\u003c/sup\u003e. Recent studies also suggest that the primary role of PIFMs during standing is to stabilize the foot joint (i.e., indirectly contribute to postural control) due to their short moment arms\u003csup\u003e\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e,\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e,\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e\u003c/sup\u003e. Nevertheless, there is little information on how PIFMs activity is associated with postural sway during tiptoe standing performed by dancers. Our previous study showed that dancers had much less postural sway and lower level/variability of PIFM activity during BTS, compared to non-dancers\u003csup\u003e\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e\u003c/sup\u003e. This suggests that BTS is not a high postural demand for dancers and that low and steady PIFM activity is associated with less postural sway. However, no studies have examined PIFM activity during STS and how it relates to postural sway in dancers.\u003c/p\u003e \u003cp\u003eThe tiptoe standing that dancers perform in daily practice and on stage requires a large ankle plantar flexion (PF) angle, which is not achievable in non-dancers, and this is even more so during STS\u003csup\u003e\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e,\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e,\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e\u003c/sup\u003e. When comparing muscle activity between individuals/conditions and examining its relationship to other parameters such as postural sway, a well-controlled task setting with the specified/same joint angle is appropriate\u003csup\u003e\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e,\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e\u003c/sup\u003e. In fact, our previous study found that PIFM activity and postural sway during BTS differed among different ankle PF angles, and the relationships between these variables were also different depending on the ankle PF angle\u003csup\u003e\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e\u003c/sup\u003e. Thus, comparing PIFM activity between STS and BTS, as well as examining its relationship with postural sway, at a large and specified ankle PF angle will shed light on dancers\u0026rsquo; postural control during tiptoe standing. However, this has never been studied. Some previous studies have used intramuscular EMG to examine PIFM activity\u003csup\u003e\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e,\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e,\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e\u003c/sup\u003e, but there are difficulties in using this technique due to its invasive nature, especially considering its potential detrimental effect on the dancers' subsequent performance. This study therefore adopted high-density EMG using a grid with multiple surface electrodes, which can noninvasively record PIFM activity across a large region of the plantar foot\u003csup\u003e\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e,\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e,\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eThe objectives of this study were to 1) compare PIFM activity and postural sway between STS and BTS conditions in dancers, and 2) examine the relationship between PIFM activity and postural sway in each condition. We hypothesized that 1) PIFM activity (its level and temporal variability) and postural sway would be significantly higher during STS than during BTS, and 2) PIFM activity would be associated with postural sway during both STS and BTS but especially the former.\u003c/p\u003e"},{"header":"Methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003eParticipants\u003c/h2\u003e \u003cp\u003eEleven female ballet dancers (age: 25.1\u0026thinsp;\u0026plusmn;\u0026thinsp;2.3 y, height: 163.9\u0026thinsp;\u0026plusmn;\u0026thinsp;6.3 cm, body mass: 47.9\u0026thinsp;\u0026plusmn;\u0026thinsp;4.9 kg, BMI: 17.8\u0026thinsp;\u0026plusmn;\u0026thinsp;1.2 kg/m\u003csup\u003e2\u003c/sup\u003e) were enrolled in this study. The participants were the same as those in our recent publication\u003csup\u003e\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e\u003c/sup\u003e, which compared postural sway and PIFM activity during BTS in dancers versus non-dancers (n\u0026thinsp;=\u0026thinsp;14 vs 13). This study reports original data for STS that was performed by eleven dancers only, while deriving the data from our previous study for BTS performed by the same eleven dancers. Dancers needed to have an at least 10 years of ballet experience and still receive at least 7.5 hours of ballet training per week. None of the participants had a history of injury or surgery in the ankle and foot joints within the past 3 months or 1 year, respectively. The study protocols complied with the principles of the Declaration of Helsinki and were approved by the Ethics Committee of Ritsumeikan University (BKC-LSMH-2021-048), and all participants provided written informed consent.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003eExperimental Protocol\u003c/h2\u003e \u003cp\u003eThe postural control task consisted of BTS for 30 seconds and STS (right leg) for 10 seconds, both at ankle PF 60\u0026deg;\u003csup\u003e\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e,\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e\u003c/sup\u003e. Electric goniometers (SG110, Biometrics, UK) were applied to measure ankle PF angles during the postural control tasks. The stationary arm of the goniometer was aligned with the long axis of the fibula in the sagittal plane, while the moving arm was aligned with the plantar plane on the side of the little toe (i.e., fifth metatarsal bone) and attached to both feet. Note that the ankle PF angle is the sum of the talocrural joint and several foot joints (Chopart\u0026rsquo;s joint, Lisfranc\u0026rsquo;s joint, etc.). The visual feedback of the goniometer data of each foot was provided in real time via two 16-bit A/D converters (PowerLab 2/20; ADInstruments, Australia) and on two PC monitors located at participants\u0026rsquo; eye level, approximately 1 m in front of them (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eA)\u003csup\u003e\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e,\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e\u003c/sup\u003e. During the STS task, the goniometer on the left (unsupported) leg was removed. Participants initially stood on a force plate (SS-FP40AO-SY, Sports Sensing, Japan). In the BTS task, they began tiptoe standing while holding the bar in front of themselves with their hands, and then removed their hands from the bar after they were able to maintain the PF angles of both feet at the specified angle as much as possible by watching the monitor so that the body mass on both feet was equal. During the BTS task, they kept both feet parallel at a comfortable stance width, with the knees fully extended, and hands relaxed on the sides of the body. In the STS task, participants started the right leg tiptoe standing with both hands holding the bar, and when they were able to maintain the PF angle at the specified angle as much as possible while watching the monitor, they removed their hands from the bar. During the STS task, the right leg was maintained in optimal turnout (i.e., external rotation of the lower limb), the left leg in retir\u0026eacute; (i.e., the left small toe on the knee joint of the right leg), and the upper limb in en avant (i.e., the upper limbs in a circular position with both fingertips in front of the trunk) (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eB). Considering the degree of postural demand, trials were performed in the order of the BTS task and then STS task. Participants performed practice trials to familiarize themselves with the procedure and subsequently performed 3 trials at each task with a rest period of at least 1 minute between trails. The average data from three successful trials were used in the data analysis. A successful trial was defined as one in which the participant was able to maintain the specified angle without grasping the bar or stepping out during the trial.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003eData Acquisition\u003c/h2\u003e \u003cp\u003eMonopolar surface EMG amplitudes from the PIFMs were acquired with a high-density grid of 64 channels (GR08MM1305, OT Bioelettronica, Italy) consisting of 13 rows and 5 columns (minus one electrode) with an 8 mm inter-electrode distance in both directions (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eA), in accordance with prior studies\u003csup\u003e\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e,\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e,\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e\u003c/sup\u003e. The right plantar skin was lightly rubbed with sandpaper and cleaned with alcohol. After palpation of the heel and metatarsal fat pads, a high-density grid was placed in the center of these areas, aligned with the long axis of the foot (i.e., second metatarsal) (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eB)\u003csup\u003e\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e,\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e,\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e\u003c/sup\u003e. The grid was reinforced with tapes to ensure consistent contact with the sole at any ankle PF angle during the tasks. Reference electrodes were placed around the right knee and left wrist. The acquired amplitudes were amplified using a 16-bit analog-to-digital converter (Quattrocento; OT Bioelectronica, Italy), with a sampling frequency of 2048 Hz and a bandpass filter of 10\u0026ndash;500 Hz (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eC). During the tasks, the COP data were acquired using the force plate and a 16-bit A/D converter (PowerLab/16SP; ADInstruments, Australia) with a sampling frequency of 1000 Hz and a low-pass filter of 5 Hz. Additionally, participants performed 5-s maximum voluntary contractions (MVCs) against manual resistance provided by one researcher twice for each of toe flexion (all toes) and toe abduction (the great and little toes), during which EMG were recorded\u003csup\u003e\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e,\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e,\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003eData Analysis\u003c/h2\u003e \u003cp\u003eThe EMG amplitude and COP data were synchronized using a trigger from a 16-bit A/D converter (PowerLab/8SP; ADInstruments, Australia). The analysis interval was 20 s excluding the first 5 s from the start of the task in the BTS task and 5 s excluding the first 2.5 s from the start of the task in the ST task. EMG signals recorded from 64 electrodes were visually inspected, and channels showing noise were reconstructed based on the interpolation of the signals from neighboring channels\u003csup\u003e\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e,\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e,\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e\u003c/sup\u003e. For each channel, the EMG root-mean-square (RMS) values during the tasks were calculated and normalized to the highest value over a 500-ms time window during the MVC tasks. The normalized EMG values were averaged across 64-channels\u003csup\u003e\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e,\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e,\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e\u003c/sup\u003e, and used as a criterion value for PIFM activity level (% MVC). From the EMG amplitude, the coefficient of variation over time (EMG-CV\u003csub\u003etime\u003c/sub\u003e) during the tasks was also calculated to evaluate the temporal variability of PIFM activity level. This was calculated by dividing the standard deviation (SD) by the mean of the EMG amplitudes during the analysis interval for each channel and then averaging over all 64 channels\u003csup\u003e\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e,\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e,\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e\u003c/sup\u003e. From the COP data, the SD in the anteroposterior and mediolateral directions (COP-SD\u003csub\u003eAP\u003c/sub\u003e and COP-SD\u003csub\u003eML\u003c/sub\u003e), average velocity (COP-Velocity), and area of a 95% confidence ellipse encompassing the COP (COP-Area) were further calculated for the analysis interval as indices of postural sway\u003csup\u003e\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e,\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e,\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003eStatistical Analysis\u003c/h2\u003e \u003cp\u003eFor all variables, the Shapiro-Wilk test was applied to assess normality, which was confirmed for all variables except for PIFM activity level and EMG-CV\u003csub\u003etime\u003c/sub\u003e in the BTS task, and COP-Area in the STS task. Therefore, between-task comparisons were made by Wilcoxon's signed rank test for these non-normally distributed variables, and by paired t-tests for the other variables. Effect sizes of between-task differences were calculated as Cohen\u0026rsquo;s d values and were interpreted as trivial\u0026thinsp;\u0026lt;\u0026thinsp;0.2; small 0.2\u0026ndash;0.49; moderate 0.5\u0026ndash;0.79; and large\u0026thinsp;\u0026ge;\u0026thinsp;0.8\u003csup\u003e26\u003c/sup\u003e. Additionally, their bootstrap 95% confidence interval (5,000 samples, bias-corrected and accelerated) was assessed by using estimation statistics to improve statistical inference\u003csup\u003e\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e\u003c/sup\u003e. To evaluate the relationship between COP variables and EMG variables in each task, Pearson's correlation coefficient and Spearman's rank correlation coefficient were calculated for normally and non-normally distributed data, respectively. Values were considered statistically significant at p\u0026thinsp;\u0026lt;\u0026thinsp;0.05. All data were analyzed using SPSS software (SPSS Statistics 28, IBM, USA) unless otherwise stated.\u003c/p\u003e \u003c/div\u003e"},{"header":"Results","content":"\u003cp\u003eCompared to the BTS task, the STS task had significantly higher COP-Velocity (BTS vs STS, 2.0\u0026thinsp;\u0026plusmn;\u0026thinsp;0.3 vs 5.1\u0026thinsp;\u0026plusmn;\u0026thinsp;0.4 cm/s, p\u0026thinsp;\u0026lt;\u0026thinsp;0.001, d\u0026thinsp;=\u0026thinsp;8.77, Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eC) and PIFM activity level (11.4\u0026thinsp;\u0026plusmn;\u0026thinsp;2.8 vs 25.8\u0026thinsp;\u0026plusmn;\u0026thinsp;7.8%MVC, p\u0026thinsp;=\u0026thinsp;0.003, d\u0026thinsp;=\u0026thinsp;2.47, Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eA). There was no significant difference between tasks in the other variables (p\u0026thinsp;=\u0026thinsp;0.093\u0026ndash;0.941, d\u0026thinsp;=\u0026thinsp;0.05\u0026ndash;0.61, Figs.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e and \u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eIn the STS task, significant correlations were found between PIFM activity level and COP-Velocity (r\u0026thinsp;=\u0026thinsp;0.666, p\u0026thinsp;=\u0026thinsp;0.025), between EMG-CV\u003csub\u003etime\u003c/sub\u003e and COP-SD\u003csub\u003eAP\u003c/sub\u003e (r\u0026thinsp;=\u0026thinsp;0.846, p\u0026thinsp;=\u0026thinsp;0.001), and between EMG-CV\u003csub\u003etime\u003c/sub\u003e and COP-SD\u003csub\u003eML\u003c/sub\u003e (r\u0026thinsp;=\u0026thinsp;0.738, p\u0026thinsp;=\u0026thinsp;0.010) (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). In the BTS task, no correlation was found between any combinations of the variables (r\u0026thinsp;=\u0026thinsp;0.097\u0026ndash;0.559, p\u0026thinsp;=\u0026thinsp;0.074\u0026ndash;0.778, Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e).\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\u003e Correlation coefficients between COP and EMG variables\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"9\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c9\" colnum=\"9\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colspan=\"2\" nameend=\"c2\" namest=\"c1\"\u003e\u0026nbsp;\u003c/th\u003e \u003cth align=\"left\" colspan=\"3\" nameend=\"c5\" namest=\"c3\"\u003e \u003cp\u003ePIFM activity level\u003c/p\u003e \u003cp\u003e (%MVC)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e\u0026nbsp;\u003c/th\u003e \u003cth align=\"left\" colspan=\"3\" nameend=\"c9\" namest=\"c7\"\u003e \u003cp\u003eEMG-CV\u003csub\u003etime\u003c/sub\u003e\u003c/p\u003e \u003cp\u003e (%)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCOP\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003ePosition\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003er\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eP\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003er\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003ep\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eSD\u003csub\u003eAP\u003c/sub\u003e (cm)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eBTS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.174\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.608\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e0.097\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e0.778\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eSTS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.083\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.808\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e0.846\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e**\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e0.001\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eSD\u003csub\u003eML\u003c/sub\u003e (cm)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eBTS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u0026minus;0.210\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.536\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e0.340\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e0.306\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eSTS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u0026minus;0.037\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.913\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e0.738\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e**\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e0.010\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eVelocity (cm/s)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eBTS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.282\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.400\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e0.559\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e0.074\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eSTS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.666\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e*\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.025\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e0.499\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e0.118\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eArea (cm\u003csup\u003e\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u003c/sup\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eBTS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.000\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e1.000\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e0.362\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e0.275\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eSTS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u0026minus;0.191\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.574\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e0.301\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e0.368\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003ctfoot\u003e \u003ctr\u003e\u003ctd colspan=\"9\"\u003eSignificance of Pearson\u0026rsquo;s correlation coefficient and Spearman's rank correlation coefficient are indicated as follows: *p\u0026thinsp;\u0026lt;\u0026thinsp;0.05, **p\u0026thinsp;\u0026lt;\u0026thinsp;0.01. COP, center of pressure; SD, standard deviation; AP, anteroposterior; ML, mediolateral; PIFM, plantar intrinsic foot muscle; EMG-CV\u003csub\u003etime\u003c/sub\u003e, temporal variability of EMG; BTS, bipedal tiptoe standing; STS, single-legged tiptoe standing.\u003c/td\u003e\u003c/tr\u003e \u003c/tfoot\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e"},{"header":"Discussion","content":"\u003cp\u003eThe main findings of this study are as follows: 1) COP-Velocity and PIFM activity level were higher in the STS than BTS task, and 2) significant correlations were found between COP and EMG variables only in the STS task. These results partially support our hypothesis and suggest that foot loading and postural demands are increased during STS compared to BTS, and that PIFM activity is particularly associated with postural sway during STS in dancers.\u003c/p\u003e \u003cp\u003eIn the present study, only COP-Velocity of the four COP variables was significantly higher in the STS than BTS task by 2.6-fold on average. This was consistent for all dancers, as shown by the individual plots in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eC. COP-Velocity represents the average distance traveled by the COP per second, regardless of the directions, and a higher value is interpreted as greater postural sway\u003csup\u003e\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e,\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e\u003c/sup\u003e. Postural stability is primarily biomechanically constrained by three conditions where: 1) the base of support is wide, 2) the line of gravity is in the center of the base of support, and 3) the center of gravity is low\u003csup\u003e\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e,\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e\u003c/sup\u003e. Compared to BTS, STS is particularly disadvantaged in conditions 1 and 2, resulting in generally higher postural demands. The results of this study suggest that this is no exception for dancers accustomed to STS. In contrast, the other three COP variables did not significantly differ between tasks. This is apparently due to inconsistent responses/patterns among dancers during STS compared to BTS, and these inter-individual variabilities suggest that there are large individual differences in their postural control strategies during the tiptoe standing tasks. More specifically, some dancers were higher but others were lower during STS than BTS in COP-SD\u003csub\u003eAP\u003c/sub\u003e (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eA), COP-SD\u003csub\u003eML\u003c/sub\u003e (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eB), and COP-Area (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eD), which are all influenced by the directions and degree of variability of the COP trajectory. Overall, these results suggest that COP-Velocity can serve as a representative variable for postural sway, and the other variables can supplement directional information, in studies adopting tiptoe standing in dancers.\u003c/p\u003e \u003cp\u003ePIFM activity level (% MVC) in the STS task was significantly higher than in the BTS task by 2.2-fold on average, and this was also consistent for all dancers (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eA). Since the body mass load on the foot is simply twice as heavy with the single-legged compared to bipedal support, it makes sense to assume that most of this increase in PIFM activity level is due to the increased foot loading. Furthermore, the correlation analysis showed that PIFM activity level was positively correlated with COP-Velocity (r\u0026thinsp;=\u0026thinsp;0.666) only in the STS task, indicating that activity level was indeed associated with postural sway particularly during STS. A study examining PIFM activity level in non-dancers reported that it was 1.5 to 1.7-fold higher in STS compared to BTS\u003csup\u003e\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e\u003c/sup\u003e. However, the tasks in that study were not compared robustly because the participants (all participants during STS and half during BTS) lightly touched a wall or other objects during postural control, and the ankle joint PF angle was not specified\u003csup\u003e\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e\u003c/sup\u003e. Taken together, the results of this study suggest that PIFM activity, particularly during STS, is dependent on foot loading and postural demands, ensuring the methodological validity of the present study that matched the PF angle during both tasks.\u003c/p\u003e \u003cp\u003eContrary to our expectations, EMG-CV\u003csub\u003etime\u003c/sub\u003e did not significantly differ between tasks (p\u0026thinsp;=\u0026thinsp;0.142), although STS on average had a 1.2-fold higher value with a borderline small/moderate effect size (d\u0026thinsp;=\u0026thinsp;0.49) (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eB). Higher and lower values of EMG-CV\u003csub\u003etime\u003c/sub\u003e reflect greater neuromuscular fluctuation and greater steadiness\u003csup\u003e\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e,\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e\u003c/sup\u003e, respectively, and therefore we expected it to be higher for STS than BTS. However, it is worth mentioning that our previous study\u003csup\u003e\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e\u003c/sup\u003e also found no significant differences in EMG-CV\u003csub\u003etime\u003c/sub\u003e during BTS performed at 20\u0026deg;, 40\u0026deg;, and 60\u0026deg; in dancers, while PIFM activity level was significantly higher for 60\u0026deg; than 20\u0026deg;, which is in line with the EMG findings of this study (i.e. different activity level, similar steadiness). In other words, these results suggest that in dancers, although PIFM activity is higher during STS than BTS, its activity is similarly steady during both STS and BTS at their respective levels. This is likely due to adaptations to dancers\u0026rsquo; daily training where they perform STS as steady as possible.\u003c/p\u003e \u003cp\u003eAlso, EMG-CV\u003csub\u003etime\u003c/sub\u003e showed a strong positive correlation with COP-SD\u003csub\u003eAP\u003c/sub\u003e and COP-SD\u003csub\u003eML\u003c/sub\u003e only in the STS task (r\u0026thinsp;=\u0026thinsp;0.846 and 0.738, Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). These suggest that PIFM activity is associated with postural sway in both directions during STS in dancers, and that these indices representing the variability of the EMG and directional COP data are sensitive to each other in the STS condition. A previous study has shown that PIFM activity during single-legged standing (with the heel on the floor) in non-dancers is synchronized with COP sway only in the mediolateral direction\u003csup\u003e\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e\u003c/sup\u003e. The reason for this discrepancy may be partly attributed to the participants being dancers vs non-dancers, but may also be explained by the combined motion of foot joints and the function of windlass mechanism due to the difference in the limb position. The foot joints have a flexibly shape-changing structure\u003csup\u003e\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e,\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e\u003c/sup\u003e, and in single-legged standing, each joint responds in a coordinated manner to postural sway, primarily in the frontal plane (i.e., mediolateral direction). For example, eversion of the subtalar joint in the hindfoot causes the combined motion such as inversion of the Chopart's and Lisfranc's joint in the mid/forefoot (and vice versa), resulting in a lowering/collapse of the medial longitudinal arch\u003csup\u003e\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e,\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e,\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e\u003c/sup\u003e. In tiptoe standing, on the other hand, the plantar fascia covering the calcaneus to the toes is tensed as the metatarsophalangeal joint is extended, resulting in the windlass mechanism that raises the medial longitudinal arch and increases joint stiffness of the foot; when this mechanism functions, the joints of the foot are unified, thus the aforementioned combined motion is reduced\u003csup\u003e\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e\u003c/sup\u003e. The present findings support recent suggestions that PIFMs are more actively involved in the windlass mechanism than previously considered\u003csup\u003e\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e,\u003cspan additionalcitationids=\"CR35\" citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e\u003c/sup\u003e, and add that their less variable (i.e., steadier) activity is associated with less postural sway during STS in dancers.\u003c/p\u003e"},{"header":"Limitations","content":"\u003cp\u003eThis study had a relatively small sample size (n\u0026thinsp;=\u0026thinsp;11), due to difficulty in recruiting professional/high-level dancers, potentially reducing statistical power. For example, our previous study\u003csup\u003e\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e\u003c/sup\u003e with a larger sample size (n\u0026thinsp;=\u0026thinsp;14) found that EMG-CV\u003csub\u003etime\u003c/sub\u003e was found to be positively correlated with COP-Velocity in the BTS task, which was not the case in either task in this study. Furthermore, both tasks in this study were compared only at the ankle PF joint angle of 60\u0026deg;, and it is unknown whether the results are generalizable to other PF joint angles. Further investigations addressing these issues are needed in the light of both kinetics and kinematic mechanics to better understand postural control of dancers.\u003c/p\u003e"},{"header":"Conclusion","content":"\u003cp\u003eIn summary, PIFM activity level and postural sway were higher during single-legged than bipedal tiptoe standing in dancers, likely due to increased foot loading and postural demands. The findings of the correlations between EMG and COP variables provide new evidence that PIFM activity is associated with postural sway during tiptoe standing in dancers, especially performed on a single leg.\u003c/p\u003e"},{"header":"Declarations","content":"\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eH.F. and S.M.: Investigation, Resources, Writing original drafts. Y.K. and T.I.: Formal analysis, Visualization, Formal analysis. Data curation.\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 on reasonable request.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eCosta MS da S, Ferreira A de S, Felicio LR. Equil\u0026iacute;brio est\u0026aacute;tico e din\u0026acirc;mico em bailarinos: revis\u0026atilde;o da literatura. \u003cem\u003eFisioterapia e Pesquisa\u003c/em\u003e. 2013;20(3):299-305. doi:10.1590/S1809-29502013000300016\u003c/li\u003e\n\u003cli\u003ede Mello MC, de S\u0026aacute; Ferreira A, Ramiro Felicio L. Postural Control During Different Unipodal Positions in Professional Ballet Dancers. \u003cem\u003eJ Dance Med Sci\u003c/em\u003e. 2017;21(4):151-155. doi:10.12678/1089-313X.21.4.151\u003c/li\u003e\n\u003cli\u003eSalzano A, Camuso F, Sepe M, Sellami M, Ardig\u0026ograve; LP, Padulo J. Acute effect of toe cap choice on toe deviation angle and perceived pain in female professional ballet dancers. \u003cem\u003eBiomed Res Int\u003c/em\u003e. 2019;2019. doi:10.1155/2019/9515079\u003c/li\u003e\n\u003cli\u003eKadel N, Boenisch M, Teitz C, Trepman E. Stability of Lisfranc joints in ballet pointe position. \u003cem\u003eFoot Ankle Int\u003c/em\u003e. 2005;26(5):394-400. doi:10.1177/107110070502600510\u003c/li\u003e\n\u003cli\u003eMcKeon PO, Hertel J, Bramble D, Davis I. The foot core system: a new paradigm for understanding intrinsic foot muscle function. \u003cem\u003eBr J Sports Med\u003c/em\u003e. 2015;49(5):290. doi:10.1136/bjsports-2013-092690\u003c/li\u003e\n\u003cli\u003eKelly LA, Kuitunen S, Racinais S, Cresswell AG. Recruitment of the plantar intrinsic foot muscles with increasing postural demand. \u003cem\u003eClinical Biomechanics\u003c/em\u003e. 2012;27(1):46-51. doi:10.1016/j.clinbiomech.2011.07.013\u003c/li\u003e\n\u003cli\u003eKurihara T, Rowley M, Reischl S, Baker L, Kulig K. Effect of a task\u0026rsquo;s postural demands on medial longitudinal arch deformation and activation of foot intrinsic and extrinsic musculature. \u003cem\u003eActa Bioeng Biomech\u003c/em\u003e. 2020;22(4):1-15. doi:10.37190/ABB-01623-2020-02\u003c/li\u003e\n\u003cli\u003eRussell JA, Shave RM, Kruse DW, Koutedakis Y, Wyon MA. Ankle and foot contributions to extreme plantar- and dorsiflexion in female ballet dancers. \u003cem\u003eFoot Ankle Int\u003c/em\u003e. 2011;32(2):183-188. doi:10.3113/FAI.2011.0183\u003c/li\u003e\n\u003cli\u003eRussell JA, Kruse DW, Koutedakis Y, Mcewan IM, Wyon MA. Pathoanatomy of Posterior Ankle Impingement in Ballet Dancers. \u003cem\u003eClinical Anatomy\u003c/em\u003e. 2010;23(6):613-621. doi:10.1002/ca.20991\u003c/li\u003e\n\u003cli\u003eFarris DJ, Birch J, Kelly L. Foot stiffening during the push-off phase of human walking is linked to active muscle contraction, and not the windlass mechanism. \u003cem\u003eJ R Soc Interface\u003c/em\u003e. 2020;17(168). doi:10.1098/rsif.2020.0208\u003c/li\u003e\n\u003cli\u003eKelly LA, Lichtwark G, Cresswell AG. Active regulation of longitudinal arch compression and recoil during walking and running. \u003cem\u003eJ R Soc Interface\u003c/em\u003e. 2015;12(102). doi:10.1098/rsif.2014.1076\u003c/li\u003e\n\u003cli\u003eFiolkowski P, Brunt D, Bishop M, Woo R, Horodyski M. Intrinsic pedal musculature support of the medial longitudinal arch: An electromyography study. \u003cem\u003eJournal of Foot and Ankle Surgery\u003c/em\u003e. 2003;42(6):327-333. doi:10.1053/j.jfas.2003.10.003\u003c/li\u003e\n\u003cli\u003eRidge ST, Rowley KM, Kurihara T, et al. Contributions of Intrinsic and Extrinsic Foot Muscles during Functional Standing Postures. \u003cem\u003eBiomed Res Int\u003c/em\u003e. 2022;2022. doi:10.1155/2022/7708077\u003c/li\u003e\n\u003cli\u003eFerrari E, Cooper G, Reeves ND, Hodson-Tole EF. Intrinsic foot muscles act to stabilise the foot when greater fluctuations in centre of pressure movement result from increased postural balance challenge. \u003cem\u003eGait Posture\u003c/em\u003e. 2020;79:229-233. doi:10.1016/j.gaitpost.2020.03.011\u003c/li\u003e\n\u003cli\u003eZhang X, Sch\u0026uuml;tte KH, Vanwanseele B. Foot muscle morphology is related to center of pressure sway and control mechanisms during single-leg standing. \u003cem\u003eGait Posture\u003c/em\u003e. 2017;57:52-56. doi:10.1016/j.gaitpost.2017.05.027\u003c/li\u003e\n\u003cli\u003eFukuyama H, Maeo S, Kusagawa Y, Ono M, Watanabe K, Isaka T. Plantar intrinsic foot muscle activity and its relationship with postural sway during tiptoe standing in ballet dancers and non-dancers. \u003cem\u003eGait Posture\u003c/em\u003e. 2024;108:139-144. doi:10.1016/j.gaitpost.2023.11.023\u003c/li\u003e\n\u003cli\u003eVieira TM, Botter A. The Accurate Assessment of Muscle Excitation Requires the Detection of Multiple Surface Electromyograms. \u003cem\u003eExerc Sport Sci Rev\u003c/em\u003e. 2021;49(1):23-34. doi:10.1249/JES.0000000000000240\u003c/li\u003e\n\u003cli\u003eWatanabe K, Vieira TM, Gallina A, Kouzaki M, Moritani T. Novel Insights into Biarticular Muscle Actions Gained from High-Density Electromyogram. \u003cem\u003eExerc Sport Sci Rev\u003c/em\u003e. 2021;49(3):179-187. doi:10.1249/JES.0000000000000254\u003c/li\u003e\n\u003cli\u003eFerrari E, Cooper G, Reeves ND, Hodson-Tole EF. Surface electromyography can quantify temporal and spatial patterns of activation of intrinsic human foot muscles. \u003cem\u003eJournal of Electromyography and Kinesiology\u003c/em\u003e. 2018;39:149-155. doi:10.1016/j.jelekin.2018.02.009\u003c/li\u003e\n\u003cli\u003eSaito S, Obata H, Kuno-Mizumura M, Nakazawa K. On the skilled plantar flexor motor action and unique electromyographic activity of ballet dancers. \u003cem\u003eExp Brain Res\u003c/em\u003e. 2018;236(2):355-364. doi:10.1007/s00221-017-5131-0\u003c/li\u003e\n\u003cli\u003eF. P. Kendall, K. McCreary, P. G. Provance. \u003cem\u003eMuscle: Testing and Function with Posture and Pain\u003c/em\u003e. 5th edition.; 2005.\u003c/li\u003e\n\u003cli\u003eLemos T, Imbiriba LA, Vargas CD, Vieira TM. Modulation of tibialis anterior muscle activity changes with upright stance width. \u003cem\u003eJournal of Electromyography and Kinesiology\u003c/em\u003e. 2015;25(1):168-174. doi:10.1016/j.jelekin.2014.07.009\u003c/li\u003e\n\u003cli\u003eKurz E, Faude O, Roth R, Zahner L, Donath L. Ankle muscle activity modulation during single-leg stance differs between children, young adults and seniors. \u003cem\u003eEur J Appl Physiol\u003c/em\u003e. 2018;118(2):239-247. doi:10.1007/s00421-017-3764-0\u003c/li\u003e\n\u003cli\u003eMoghadam M, Ashayeri H, Salavati M, et al. Reliability of center of pressure measures of postural stability in healthy older adults: Effects of postural task difficulty and cognitive load. \u003cem\u003eGait Posture\u003c/em\u003e. 2011;33(4):651-655. doi:10.1016/j.gaitpost.2011.02.016\u003c/li\u003e\n\u003cli\u003ePalmieri RM, Ingersoll CD, Stone MB, Krause BA. Center-of-Pressure Parameters Used in the Assessment of Postural Control. \u003cem\u003eJ Sport Rehabil\u003c/em\u003e. 2002;11(1):51-66. doi:10.1123/jsr.11.1.51\u003c/li\u003e\n\u003cli\u003eCohen J. \u003cem\u003eStatistical Power Analysis for the Behavioral Sciences\u003c/em\u003e. Routledge; 2013. doi:10.4324/9780203771587\u003c/li\u003e\n\u003cli\u003eHo J, Tumkaya T, Aryal S, Choi H, Claridge-Chang A. Moving beyond P values: data analysis with estimation graphics. \u003cem\u003eNat Methods\u003c/em\u003e. 2019;16(7):565-566. doi:10.1038/s41592-019-0470-3\u003c/li\u003e\n\u003cli\u003eNashner LM, McCollum G. The organization of human postural movements: A formal basis and experimental synthesis. \u003cem\u003eBehavioral and Brain Sciences\u003c/em\u003e. 1985;8(1):135-150. doi:10.1017/S0140525X00020008\u003c/li\u003e\n\u003cli\u003eHorak FB. Postural orientation and equilibrium: what do we need to know about neural control of balance to prevent falls? \u003cem\u003eAge Ageing\u003c/em\u003e. 2006;35(suppl_2):ii7-ii11. doi:10.1093/ageing/afl077\u003c/li\u003e\n\u003cli\u003eNeumann DA. \u003cem\u003eKinesiology of the Musculoskeletal System: Foundations of Rehabilitation.3rd Ed. \u003c/em\u003e.; 2017.\u003c/li\u003e\n\u003cli\u003eRazeghi M, Batt ME. Foot type classification: a critical review of current methods. \u003cem\u003eGait Posture\u003c/em\u003e. 2002;15(3):282-291. doi:10.1016/S0966-6362(01)00151-5\u003c/li\u003e\n\u003cli\u003eMulligan EP, Cook PG. Effect of plantar intrinsic muscle training on medial longitudinal arch morphology and dynamic function. \u003cem\u003eMan Ther\u003c/em\u003e. 2013;18(5):425-430. doi:10.1016/j.math.2013.02.007\u003c/li\u003e\n\u003cli\u003eHicks JH. The mechanics of the foot. II. The plantar aponeurosis and the arch. \u003cem\u003eJ Anat\u003c/em\u003e. 1954;88(1):25-30.\u003c/li\u003e\n\u003cli\u003eWelte L, Kelly LA, Lichtwark GA, Rainbow MJ. Influence of the windlass mechanism on arch-spring mechanics during dynamic foot arch deformation. \u003cem\u003eJ R Soc Interface\u003c/em\u003e. 2018;15(145):20180270. doi:10.1098/rsif.2018.0270\u003c/li\u003e\n\u003cli\u003eKelly LA, Farris DJ, Cresswell AG, Lichtwark GA. Intrinsic foot muscles contribute to elastic energy storage and return in the human foot. \u003cem\u003eJ Appl Physiol\u003c/em\u003e. 2019;126:231-238. doi:10.1152/japplphysiol.00736.2018.-The\u003c/li\u003e\n\u003cli\u003eRiddick R, Farris DJ, Kelly LA. The foot is more than a spring: Human foot muscles perform work to adapt to the energetic requirements of locomotion. \u003cem\u003eJ R Soc Interface\u003c/em\u003e. 2019;16(150). doi:10.1098/rsif.2018.0680\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"scientific-reports","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"scirep","sideBox":"Learn more about [Scientific Reports](http://www.nature.com/srep/)","snPcode":"","submissionUrl":"","title":"Scientific Reports","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Scientific Reports","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"high-density electromyography, temporal variability, postural sway, center of pressure, foot","lastPublishedDoi":"10.21203/rs.3.rs-4702997/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-4702997/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"During tiptoe standing, especially with the single-legged support, the foot joints in ballet dancers are heavily loaded. Thus, the activity of the plantar intrinsic foot muscles (PIFMs), which stabilize the foot joints, may be important in reducing postural sway during tiptoe standing. We compared PIFM activity during single-legged and bipedal tiptoe standing and examined its relationship to postural sway in dancers. In 11 female ballet dancers, the electromyography (EMG) amplitudes of PIFMs and the center of pressure (COP) data were recorded during single-legged and bipedal tiptoe standing tasks. The EMG amplitudes were normalized to those during the maximal voluntary contraction, and PIFM activity level and its coefficient of variation over time (EMG-CVtime) during the task were assessed. From the COP data, standard deviations in the anteroposterior (COP-SDAP) and mediolateral (COP-SDML) direction, velocity, and area were calculated. PIFM activity level and COP velocity were 2–2.5-fold higher in the single-legged than bipedal task (p≤0.003). Significant correlations were found between PIFM activity level and COP velocity (r=0.666, p=0.025) and between EMG-CVtime and COP-SDAP or COP-SDML (r≥0.738, p≤0.010) only in the single-legged task. These results suggest that PIFM activity is associated with postural sway, especially during single-legged tiptoe standing in dancers.","manuscriptTitle":"Plantar intrinsic foot muscle activity and its relationship with postural sway during single-legged and bipedal tiptoe standing in ballet dancers","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-08-02 06:54:46","doi":"10.21203/rs.3.rs-4702997/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2025-04-21T02:18:18+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-04-19T05:15:10+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"271313552398290709366235022102930778299","date":"2025-03-25T17:17:56+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2024-10-20T18:38:20+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"208265731004167371150970873043701553452","date":"2024-10-14T06:38:25+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"108717384547650773577400399394588382163","date":"2024-10-13T12:16:37+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2024-10-12T08:04:56+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2024-10-08T13:00:26+00:00","index":"","fulltext":""},{"type":"editorInvited","content":"","date":"2024-07-10T07:36:45+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2024-07-10T07:31:39+00:00","index":"","fulltext":""},{"type":"submitted","content":"Scientific Reports","date":"2024-07-08T06:11:06+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"scientific-reports","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"scirep","sideBox":"Learn more about [Scientific Reports](http://www.nature.com/srep/)","snPcode":"","submissionUrl":"","title":"Scientific Reports","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Scientific Reports","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"38962f1f-4992-4553-b76e-4fbfef305f4c","owner":[],"postedDate":"August 2nd, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[{"id":35398904,"name":"Biological sciences/Neuroscience"},{"id":35398905,"name":"Health sciences/Anatomy"}],"tags":[],"updatedAt":"2025-05-26T16:05:04+00:00","versionOfRecord":{"articleIdentity":"rs-4702997","link":"https://doi.org/10.1038/s41598-025-02917-9","journal":{"identity":"scientific-reports","isVorOnly":false,"title":"Scientific Reports"},"publishedOn":"2025-05-23 15:58:40","publishedOnDateReadable":"May 23rd, 2025"},"versionCreatedAt":"2024-08-02 06:54:46","video":"","vorDoi":"10.1038/s41598-025-02917-9","vorDoiUrl":"https://doi.org/10.1038/s41598-025-02917-9","workflowStages":[]},"version":"v1","identity":"rs-4702997","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-4702997","identity":"rs-4702997","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}