Combining neuromuscular electrical stimulation and action observation to promote sensorimotor adaptation in healthy older adults: a study protocol on a self-administered home-based intervention

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Data may be preliminary. 3 October 2025 V1 Latest version Share on Combining neuromuscular electrical stimulation and action observation to promote sensorimotor adaptation in healthy older adults: a study protocol on a self-administered home-based intervention Authors : Andrea Albergoni , Pasquale Salerno , Monica Biggio , Marco Bove , and Ambra Bisio 0000-0002-9385-1714 [email protected] Authors Info & Affiliations https://doi.org/10.22541/au.175952325.55222026/v1 200 views 114 downloads Contents Abstract Information & Authors Metrics & Citations View Options References Figures Tables Media Share Abstract Aging is associated with a decline in muscle strength and the functionality of the perceptual structures involved in proprioception. This decline results in a gradual loss of autonomy in daily activities. Neuromuscular electrical stimulation (NMES) has been shown to be an effective technique in limiting the decline in strength. Action observation (AO) is a cognitive technique, which has been shown to improve motor performance, especially when combined with peripheral stimulation. The purpose of this study is to evaluate whether an self-administered, home-based intervention combining NMES and AO improves upper limb muscle strength and proprioceptive abilities in healthy elderly individuals. Participants within the age range of 65–85 years will be recruited for this study. The intervention is scheduled to span a duration of four weeks, encompassing three treatment sessions per week. Participants will be randomly divided into three groups: NMES, AO, and AO-NMES. Assessments will be performed before and immediately after the intervention. They will include muscle strength evaluation (handgrip strength, maximal isometric force of the biceps, bench press power), and perceptual evaluation (weight discrimination during an AO task, weight judgment tasks). This study may suggest an original approach, cost-effective approach to mitigate the effects of physiological aging on muscle and sensorimotor function, with potential applications for frail populations, unable or unmotivated to perform conventional physical activity. Combining neuromuscular electrical stimulation and action observation to promote sensorimotor adaptation in healthy older adults: a study protocol on a self-administered home-based intervention Andrea Albergoni 1, Pasquale Salerno 2, Monica Biggio2, Marco Bove 1,3, Ambra Bisio 1* 1 Department of Experimental Medicine, Section of Human Physiology, University of Genoa, Genoa, Italy 2 Department of Neuroscience, Rehabilitation, Ophthalmology, Genetics and Maternal Child Health, University of Genoa, Genoa, Italy 3 IRCCS Ospedale Policlinico San Martino, Genoa, Italy * corresponding author Prof. Ambra Bisio, Department of Experimental Medicine, Section of Human Physiology, University of Genoa, viale Benedetto XV, 3, 16132, Genoa, Italy. E-mail: [email protected] Abstract Aging is associated with a decline in muscle strength and the functionality of the perceptual structures involved in proprioception. This decline results in a gradual loss of autonomy in daily activities. Neuromuscular electrical stimulation (NMES) has been shown to be an effective technique in limiting the decline in strength. Action observation (AO) is a cognitive technique, which has been shown to improve motor performance, especially when combined with peripheral stimulation. The purpose of this study is to evaluate whether an self-administered, home-based intervention combining NMES and AO improves upper limb muscle strength and proprioceptive abilities in healthy elderly individuals. Participants within the age range of 65–85 years will be recruited for this study. The intervention is scheduled to span a duration of four weeks, encompassing three treatment sessions per week. Participants will be randomly divided into three groups: NMES, AO, and AO-NMES. Assessments will be performed before and immediately after the intervention. They will include muscle strength evaluation (handgrip strength, maximal isometric force of the biceps, bench press power), and perceptual evaluation (weight discrimination during an AO task, weight judgment tasks). This study may suggest an original approach, cost-effective approach to mitigate the effects of physiological aging on muscle and sensorimotor function, with potential applications for frail populations, unable or unmotivated to perform conventional physical activity. Keywords : aging; physical fitness; strength; weight estimation Introduction Aging leads to a natural decline in strength, muscle mass, and associated functions. This gradual degradation could lead to sarcopenia by affecting the health-related quality of life. Indeed, muscle weakness is one of the most documented and it is at the origin of impairments in instrumental activities of daily living (IADL). In aging, in addition to deterioration of contractile structures, there is also deterioration of sensory structures, such as muscle spindles and Golgi tendon organs (Fan et al., 2021), which are structures that conveys proprioceptive information related to the sense of effort, force, and heaviness (Proske & Gandevia, 2012) at the supraspinal level, whose deterioration may alter proprioception in aging (Henry & Baudry, 2019). Muscle mass and muscle-related sensory functions have been shown to be closely linked. In particular, evidence indicates a correlation between muscle weakness and proprioceptive dysfunction (Butler et al., 2008). In light of the link between motor and sensory processes, it is reasonable to hypothesise that muscle-strengthening protocols have a positive effect on both motor and proprioceptive functions, possibly delaying a functional decline due to physiological aging (Halma et al., 2025). Older people, however, face many barriers in accessing and maintaining adequate levels of physical activity (Meredith et al., 2023). Neuromuscular electrical stimulation (NMES) could be an effective way of mitigating the effects of physical inactivity, as it is relatively inexpensive and can be done at home. Indeed, elderly population reported preferring autonomy and flexibility in the administration of interventions, often opting for unsupervised, home-based NMES sessions (O’Connor et al., 2018). This technique was largely used in different populations with or without force deficit, and is recognised as an effective and safe approach to containing the decline in muscle strength due to aging (O’Connor et al., 2018). NMES causes physiological adaptations including an increased muscle protein synthesis (Wall et al., 2012), and central activation of sensory and motor areas (Maffiuletti et al., 2018). Another advantage of using NMES is its ability to preferentially activate type II muscle fibers (Bickel et al., 2011), which are particularly vulnerable to age-related decline (Brunner et al., 2007). This decline contributes to reduced muscle power and impaired proprioception. Both muscle power and proprioception, which deserve greater attention when addressing the needs of the elderly population, are strongly associated with functional performance than muscular strength alone (Byrne et al., 2016). Concerning the way of applying NMES, positive results in term of its effectiveness on muscle strength has been shown when applied alone, when combined to a physical training and nutritional therapy (Langeard et al., 2017; Ikeda et al., 2023). This is in line with recent neuroscientific evidence suggesting that an integrated approach combining peripheral stimulation (e.g., electrical nerve stimulation and muscle-tendon vibration) and cognitive stimulation, such as action observation (AO), plastically stimulates the sensorimotor system similarly to movement execution causing a long-lasting increase in the primary motor cortex excitability and improvements in the motor performance (Bisio, Avanzino, Gueugneau, et al., 2015; Bisio, Avanzino, Lagravinese, et al., 2015; Bisio et al., 2019). AO is known to activate a cortical and subcortical network that largely overlaps with the one engaged during actual movement execution (Henschke & Pakan, 2023). Similarly, a superimposition of brain areas has been shown between movement execution and peripheral stimulations, such as electrical nerve stimulation and muscle-tendon mechanical vibration (Romaiguère et al., 2003; Perasso et al., 2019). Furthermore, the combination of AO and peripheral stimulation have been shown to activate a superimposed frontoparietal cortical network, which may account for their combined ability to induce plastic modulation of cortical excitability (Romaiguère et al., 2003). Notably, this network substantially overlaps with that involved in actual movement execution, which may further explain their effectiveness in promoting both cortical plasticity and motor learning (Hardwick et al., 2018). In these studies, AO was always administered concurrently to the peripheral stimulation. However, its efficacy in promoting motor learning has also been demonstrated when AO precedes movement execution, suggesting that the temporal proximity between these two events may play a significant impact in the consolidation of AO effects (Bove et al., 2009). These premises support the hypothesis that the combined application of AO and NMES may produce a more pronounced enhancement in muscle strength and, in turn, improvement in proprioceptive abilities, particularly those related to the sense of effort and heaviness, leading to a more effective management of IADLs than when either technique is used in isolation. In the healthy elderly population, the use of NMES has primarily focused on the lower limbs, as lower limb strength tends to decline more rapidly than upper limb strength (Langeard et al., 2017). Consequently, despite its relevance for IADL performance, the effectiveness of NMES applied on the upper limbs remains less well-established. The purpose of study will be testing the effects of a self-administered, home-based intervention combining NMES and AO for the upper limbs in healthy elderly people on muscle strength and proprioceptive abilities. This will be done by comparing AO-NMES with AO and NMES delivered alone, with the hypothesis that AO-NMES leads to higher improvement than the others. This approach could be a safe, accessible and cost-effective way to maintain or improve neuromuscular function and sensorimotor control in ageing populations. Furthermore, by preserving upper limb function, the intervention could help older adults to retain functional autonomy, reduce their risk of disability and improve their overall quality of life and well-being. Methods The study was approved by the local ethics committee (Comitato Etico per la Ricerca di Ateneo – CERA, Prot. N° 2024/22, 13/03/2024). It will follow the ethical standards outlined in the Declaration of Helsinki and its subsequent amendments. Sample size calculation An a priori power analysis was conducted using G_Power version 3.1.9.7 to determine the minimum sample required to test the study hypothesis. The effect size was set at 0.40 considered to be medium using Cohen’s criteria. A F-test assessing the interaction between the groups (n = 3) and the repeated measurements (n = 2) was applied with a significance criterion of a = 0.05 and power = 0.80. The minimum sample size needed was N = 21 (7 per group) to detect differences in muscular strength. To ensure sufficient power despite potential dropouts, a minimum of 10 participants will be recruited per group. Participants Voluntarily participants will be recruited from the students enrolled in the ‘UniGeSenior’ program at the University of Genoa. The inclusion criteria are voluntarily participation, age ranges from 65 to 85 years, both male and female. Exclusion criteria are neurological disorders, psychiatric disorders, fractures within the previous 6 months, orthopaedic or musculoskeletal impairments, uncontrolled hypertension, resistance training involving the upper limbs performed at least once per week. Study design This will be a randomized, double-blind, controlled experimental trial. The intervention will last four weeks, three sessions per weeks will be performed at home. The intervention will vary according to the assigned group, with all interventions delivered in parallel across the following groups: AO group, NMES group and AO-NMES group. The assignment will be done using the RAND() function in Excel, which generated random numbers that were then used to sort and allocate subjects evenly. During each session, the treatment will last 30 minutes and will include a 10-minutes warm-up phase during which the visual task will be administered, and 20 minutes of exercise phase. Before (PRE) and after (POST) the intervention period participant will perform different kinds of assessments (see Evaluation section) (Figure 1). — Figure 1 here — Intervention Visual stimuli The stimuli shown to the participants will change according to the group. In the AO group participants will watch a video showing different IADLs, which require considerable force production, executed with the upper limbs by a woman or a man. The IADLs will involve the individual performing the following tasks: Moving a box forward or backward while sitting on a chair Lifting a box onto or bringing it down from a support while standing upright Placing a box onto or removing it from a shelf while standing upright Moving a box from left to right or right to left while sitting on a chair Moving a shopper from right to left or left to right while standing upright Placing a shopper on a shelf or taking it down from a standing position Holding a shopper while remaining upright Frame of the displayed actions are represented in Figure 2. The same AO task will be proposed to the AO-NMES group. Participants of the NMES group will observe changing landscapes. The visual stimuli will be administered through a tablet (Smartpad 9 Mediacom, Datamatic S.p.A, Milano, Italy) provided to the participants. — Figure 2 here — NMES parameters During the first day of intervention, participant will receive the NMES medical device (I-TECH PHYSIO, IACER srl, Scorzè, Venice, Italy) and will be instructed on how to use it by a researcher expert in sport science. During the warm-up phase, the NMES will be set with a frequency of 50 Hz and a pulse duration at 400 μs and the intensity at motor threshold. During the exercise phase, participants in the AO group will receive a NMES sham treatment (f=5Hz, t=100 μs) delivered at sensory threshold (Insausti-Delgado et al., 2021), and known to be ineffective in increasing muscle strength (Vivodtzev et al., 2012). In the NMES and AO-NMES groups, the exercise phase will be administered at functional threshold (the minimum intensity required for a complete arm flexion (Insausti-Delgado et al., 2021)) or at maximal tolerated intensity (f=100Hz, t=400 μs). Evaluations Evaluations will include collection of personal data (year of birth, clinical status, years of education, weight and height) strength assessment, weight discrimination during an AO task, and weight judgment task. They will be performed on the same day, with appropriate rest periods between each evaluation. One week before the PRE evaluation, in a familiarization session, participants will perform the strength assessment, the familiarization was recommended with elderly people (Alcazar et al., 2018). Evaluations will be conducted by two researchers with expertise in sport science, who will be blinded to the type of intervention performed by the participants. Possible harms will be recorded non-systematically based on spontaneous reports from participants during the experimental period. Strength assessment The aim of this test is to assess the effectiveness of the three interventions in increasing muscle strength and power. The handgrip strength (kg) of the participants will be assessed with the KERN MAP handgrip dynamometer (KERN & SOHN GmbH). The participants will execute the test standing, with the shoulder adducted, the elbow extended, the forearm and the wrist neutral. They will be required to grip the dynamometer with their maximum strength. The mean value obtained from three repetitions will be considered to assess the right and left handgrip strength. The mean values between left and right handgrip strength will be considered as the outcome parameter of handgrip strength. During the familiarization session, participants will familiarize with the isometric curl and the bench press test. Regarding the first test, participants perform 10 submaximal repetitions and 3 maximal repetitions. Regarding the second test, they perform two sets of eight to ten repetitions at a submaximal load of bench press, followed by two sets of two repetitions at maximal speed with an empty bar. During the evaluation, the assessment of biceps maximal isometric force (MIF, N) will be performed using the Chronojump force sensor (Chronojump, Barcelona, Spain) asking participant to perform an elbow flexion. Participants will be assessed from sitting position, holding a bar with both supinated and elbow angle approximately at 90°. The bar will be connected to the force sensor by a static rope. The movement will be executed three times, with 1-minute pause between each repetition. Participants will be instructed to pull as hard as possible to maintain the contraction for at least 2 s with verbal encouragement. The trial with the highest MIF value will be considered as valid. Before the evaluation, a warm-up phase consisting in a set of five repetitions at the loads of 40-60% of the perceived maximum force (Alcazar et al., 2018) will be performed. Bench press test will be executed to assess the force-velocity relationship, and to estimate the maximal power. The test will be preceded by a warm-up consisting of two sets of 10 repetitions at the Smith Machine. During the execution of traditional bench press, participants will stop the bar to the chest for 2 seconds and then will push the bar as fast as possible until the full extension of the elbow (Iglesias-Soler et al., 2019). The initial load will be set at 16kg for male and 12kg for female. The load will constantly increase to perform 3-4 sets, number of sets required to obtain an adequate estimate of maximum power, with an execution speed in the last set lower than 0.3 m⋅s− 1 (Alcazar et al., 2017). Between each set, 3 minutes of rest will be applied. During this test a linear position transducer will be used (Chronojump, Barcelona, Spain). One end will be attached on the left side of the bar, and the other end will be fixed to the floor. Maximal Power will be extracted with Chronojump software. Weight judgment task The aim of this evaluation is to test the perceived heaviness of an object in a daily life context with the hypothesis that AO-NMES treatment will have positive effect on proprioceptive ability. A point weight judgement task will be performed. The participants will be instructed to judge the weight of a box in kilograms. A one-kilo box will be used for familiarization of the task. Participants will lift the box, positioned in front of them on a table with the handles aligned at hip level, using arm flexion until approximately 45° of flexion is reached. The box used during the weight judgment task will be filled with cast-iron disk, secured to prevent movement, to reach a weight of 4 kg, 7 kg and 10 kg. Participants will not be given information about weights or the number of different weights. Each box will be lifted 5 times. The mean values weight reported by the participant and coefficient of variations will be considered as outcome parameters together with the estimation error computed as the absolute difference between the real and the perceived weight. Weight discrimination during an AO task The aim of this test is to evaluate participants’ ability to discriminate the weight of an object moved by others during an action observation task. The hypothesis is that by improving both strength and the perception of heaviness, this enhanced ability will transfer to the motor resonance mechanism (Albergoni, Biggio, Faelli, Pesce, et al., 2023), thereby assisting participants in accurately evaluating the weight of an object moved by another individual. The weight-discrimination video task is described in a previous paper of our group (Albergoni, Biggio, Faelli, Ruggeri, et al., 2023). Briefly, participants will have to discriminate the weight of two boxes moved in two consecutive actions displayed in a video indicating which is the heaviest box. One of the videos is used as a reference. The weight inside the box in this video is 7 kg. In the other video, the weight inside the box varied from 0 to 15 kg. The number of trials is 112 (16 repetitions for 7 box weight). Just Noticeable Differences (JND), obtained by the psychometric function, will be the outcome parameter. Monitoring adherence to the protocol To monitor participants’ adherence to the protocol, a researcher will call each participant at the end of every intervention week to ask whether all planned sessions for that week were completed. The reported number of completed sessions will be recorded to support data interpretation. Statistical analysis The participants sociodemographic characteristic will be presented using descriptive statistics. Data from participants who will not end the intervention period will not be included in the analysis. Shapiro-Wilk test was applied to evaluate data distribution and Levene’s test was used to evaluate the equality of variances. The primary outcome variable will be the MIF. Secondary outcome variables will be handgrip strength, perceived weight, coefficient of variation and estimation error. Linear mixed models with Time (2 levels, Pre and Post) and Group (3 levels, AO, AO-NMES and NMES) as fixed factors and Participants as random factor, will be applied on will with, MIF, power and JND. A Linear mixed models with Time (2 levels, Pre and Post), Weight (3 levels, 4kg, 7kg, 10kg) and Group (3 levels, AO, AO-NMES and NMES) as fixed factors and Participants as random factor will be applied on perceived weight, coefficient of variation and estimation error. Bonferroni post hoc tests will be applied in case of significant interaction or main effect with more than two levels. Discussion This study introduces a novel approach to induce sensorimotor adaptation in healthy older individuals by testing the efficacy of a self-administered, home-based intervention that combined NMES and AO. Numerous studies had shown the effectiveness of NMES intervention protocols in healthy elderly individuals (Langeard et al., 2017). NMES has been shown to cause strength improvements comparable to those from traditional resistance training either at rest or during voluntary contractions (Langeard et al., 2017). NMES training therefore appears to be an ideal way to counteract functional decline in the elderly and strongly recommended to be included into adapted physical activity intervention in elderly population (Langeard et al., 2017). The duration of and frequency of our intervention (4 week-program with 3 trainings per week) was suggested to be enough to elicit positive effects (Langeard et al., 2017). Also, AO training seems to be an efficient strategy in enhancing the effectiveness of conventional motor rehabilitation (Sarasso et al., 2015). In turn, when associated with peripheral stimulation AO has been shown to promote cortical plasticity and motor learning (Bisio, Avanzino, Gueugneau, et al., 2015; Bisio, Avanzino, Lagravinese, et al., 2015; Bisio et al., 2019). Based on these premises, AO is expected to enhance effectiveness of NMES, leading to greater increases in strength and power than those induced by NMES or AO alone. At the same time, this motor improvement will be reflected in the perceived sense of heaviness, as well as in the ability to discriminate the weight of an object based on observed movement—both of which are features related to proprioception. All these sensorimotor adaptations may positively impact participants’ quality of life by improving and extending their autonomy in performing IADLs. In conclusion, this study may suggest new applications for techniques such as AO in supporting maintenance or improvement of strength resulting from NMES training in elderly population. The home-based, self-administered nature of the protocol ensures high ecological validity, making it suitable for large-scale use, even in areas with limited access to rehabilitation services. This study could also create opportunities for future applications in clinical populations exhibiting early signs of neuromotor decline. Acknowledgments This project has been funded by the European Union – Next Generation EU, Mission 4, Component 2, Investment 1.01, under grant code 202284WCP9, CUP D53D23009440001 (call PRIN 2022). The authors thank the UniGe Senior and the “Centro interdipartimentale per la longevità e per l’invecchiamento attivo” (CILIA) of the University of Genoa, Italy for its cooperation. Conflicts of Interest The authors declare no conflicts of interest. Data Availability Statement Data to be collected in this study will be made available by the authors upon reasonable request. Ethics Statement The study was approved by the local ethics committee (Comitato Etico per la Ricerca di Ateneo – CERA, Prot. N° 2024/22, 13/03/2024). It will follow the ethical standards outlined in the Declaration of Helsinki and its subsequent amendments. References Albergoni, A., Biggio, M., Faelli, E., Pesce, A., Ruggeri, P., Avanzino, L., Bove, M., & Bisio, A. (2023) Sensorimotor expertise influences perceptual weight judgments during observation of a sport-specific gesture. Front. Sport. Act. Living, 5, 1148812.Albergoni, A., Biggio, M., Faelli, E., Ruggeri, P., Avanzino, L., Bove, M., & Bisio, A. (2023) Aging deteriorates the ability to discriminate the weight of an object during an action observation task. Front. Aging Neurosci., 15, 1216304.Alcazar, J., Guadalupe-Grau, A., García-García, F.J., Ara, I., & Alegre, L.M. 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Frames from the videos depicting each action of the instrumental activities of daily living presented to the participants in the AO-NMES and AO groups. Information & Authors Information Version history V1 Version 1 03 October 2025 Copyright This work is licensed under a Non Exclusive No Reuse License. Keywords aging physical fitness strength weight estimation Authors Affiliations Andrea Albergoni Università degli Studi di Genova View all articles by this author Pasquale Salerno Università degli Studi di Genova View all articles by this author Monica Biggio University of Genoa View all articles by this author Marco Bove Università degli Studi di Genova View all articles by this author Ambra Bisio 0000-0002-9385-1714 [email protected] Università degli Studi di Genova View all articles by this author Metrics & Citations Metrics Article Usage 200 views 114 downloads .FvxKWukQNSOunydq8rnd { width: 100px; } Citations Download citation Andrea Albergoni, Pasquale Salerno, Monica Biggio, et al. Combining neuromuscular electrical stimulation and action observation to promote sensorimotor adaptation in healthy older adults: a study protocol on a self-administered home-based intervention. Authorea . 03 October 2025. 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