Short-Term Neuromuscular Electrical Stimulation for Muscle... : Exercise, Sport, and Movement (original) (raw)
INTRODUCTION
Skeletal muscle atrophy is commonly associated with aging, inactivity, and disuse conditions such as bed rest, malnutrition, and sometimes microgravity (1). During hospitalization, muscle loss is most pronounced in the lower limbs, particularly in the rectus femoris (RF) and gastrocnemius (GAS) (2), and this decline accelerates with the duration of disuse (3). Notably, significant reductions in the muscle cross-sectional area have been observed within the first week of bed rest (4), and approximately 50% of the total decline in lower-limb strength during 17 wk of bed rest occurs in this initial week (2). Additionally, in healthy young men, 1 wk of bed rest has been shown to result in a 3.2% decrease in quadriceps cross-sectional area, corresponding to a loss of 1.4 ± 0.2 kg of lean mass, equivalent to the muscle gained after 12 wk of progressive resistance training (5). This early-phase atrophy is even more concerning in older adults whose skeletal muscle plasticity is already significantly diminished (6). Sarcopenia, the age-related loss of muscle mass, is exacerbated by immobilization, even over short periods, leading to functional impairment (3,7), increased frailty, and a higher risk of falls (8,9). Therefore, brief hospital stays can result in walking difficulties and reduced independence in this population.
Although high-intensity resistance training is effective in preventing muscle loss and frailty (10,11), it is often poorly tolerated by older individuals due to pain and discomfort (12,13), resulting in low adherence (14). More than 20% of older participants in resistance training trials drop out (14), indicating that this approach may not be practical for individuals with limited motivation or interest in exercise.
Neuromuscular electrical stimulation (NMES) has emerged as a promising alternative for patients unable to engage in active exercise. NMES passively induces muscle contractions, yielding outcomes comparable to those obtained via exercise, regardless of the voluntary effort of the individual. Previous studies have demonstrated that combining NMES with exercise therapy for 6–16 wk improves muscle size and function in community-dwelling older adults and those in nursing homes who are independent in daily living (15–17). However, although several studies have demonstrated the benefits of NMES over longer intervention periods, evidence from randomized controlled trials focusing on its short-term effects during the early phase of bed rest in frail older adults is still limited. This is a clinically important gap because early intervention during bed rest may prevent rapid deterioration of muscle mass and strength.
Therefore, the aim of this study was to determine whether the combination of NMES and exercise therapy can attenuate the muscle atrophy and weakness induced by 1 wk of bed rest in hospitalized older adults. We hypothesized that NMES combined with exercise therapy would significantly attenuate muscle mass and strength loss compared with exercise therapy alone. Our treatment protocol has the potential to provide sufficient exercise volume to prevent muscle atrophy and weakness, even in patients with cognitive impairment or poor motivation who cannot achieve sufficient volume with standard (active) exercise therapy.
METHODS
Participants
Participant recruitment was conducted from June 23, 2022, to March 31, 2023. A total of 20 older female patients with spinal compression fractures who were admitted to a general hospital between June 28, 2022, and March 20, 2023, were enrolled. No patient had a history of major complications such as diabetes or cardiovascular disease or had been hospitalized within the year preceding the study, except for temporary admissions. Following admission, all patients were prescribed at least 1 wk of bed rest and were unable to sit or stand during this period.
Eligibility criteria for participation were as follows: 1) age ≥65 yr, 2) ability to maintain a standing position before hospitalization, 3) ability to understand exercise instructions, and 4) medical evaluation confirming that 1 wk of bed rest was required. Exclusion criteria were as follows: 1) contraindications for NMES, such as bleeding or skin damage at the stimulation site; 2) history of cerebrovascular disease or orthopedic surgery of the lower extremities; 3) presence of hypertension, tachycardia, or bradycardia on the day of evaluation; and 4) discharge from the hospital during the study period.
An a priori power analysis was conducted using G*Power software (version 3.1.9.7; Heinrich Heine Universität Düsseldorf, Düsseldorf, Germany) (18). A repeated-measures analysis of variance (ANOVA) was used with a within–between design, with the group × time interaction as the effect of interest. To ensure a large effect size, we specified Cohen’s f = 0.40, which corresponds to a partial _η_² of 0.14 and represents a large effect according to Cohen’s guidelines (19). Under these conditions, with α = 0.05 and power (1 − β) = 0.80, the required sample size was determined to be 16. To account for potential dropouts, we increased the target enrollment to 20 participants. Importantly, this estimated sample size is consistent with previous intervention studies involving patients undergoing bed rest and strikes a balance between facilitating the attainment of adequate statistical power and maintaining feasibility (20,21).
All enrolled participants completed the intervention and outcome assessments; no dropouts occurred during the study period. This study was approved by the Ethics Committee of the Open University of Japan (approval no. 2022-6) and registered in the UMIN Clinical Trials Registry (registry ID: UMIN000048532). All procedures were conducted in accordance with the Declaration of Helsinki, and written informed consent was obtained from all participants.
Interventions
This study was a single-blind randomized controlled trial with a 1:1 allocation ratio. A total of 20 patients were randomly assigned to one of two groups: the exercise therapy group, which received only exercise therapy, or the exercise therapy + NMES group, which received both exercise therapy and NMES. The intervention period was 1 wk for both groups, and the patients received their assigned intervention daily.
Randomization procedures were conducted in accordance with the Consolidated Standards of Reporting Trials guidelines (22). A random allocation sequence was generated using opaque, sealed envelopes, with the first participant randomly assigned to either the exercise therapy group or the exercise therapy + NMES group. Subsequent participants were alternately assigned to the groups based on this initial allocation. Allocation concealment was ensured by using sequentially numbered, opaque, sealed envelopes prepared in advance. Randomization and group allocation were performed by an independent therapist at the clinic who was not involved in the recruitment, intervention, or outcome assessment and who was blinded to the study’s objectives and expected outcomes. Interventions were administered by a therapist who was also blinded to group allocation. The participant recruitment process is shown in the flow chart in Figure 1.
Study enrollment flow chart.
Exercise Therapy Group
Patients underwent 80 min of exercise therapy, consisting of range-of-motion exercises and strength training targeting the hip, knee, and ankle muscles in a supine position. The intensity of the strength training was set at 60% of the maximum voluntary contraction (MVC), as determined by a manual dynamometer (Moby, MT-100; Sakai Medical Co., Ltd., Tokyo, Japan). During the therapy sessions, participants performed a total of 200 repetitions each of knee extension and ankle plantar flexion.
Exercise Therapy + Neuromuscular Electrical Stimulation Group
Patients assigned to the exercise therapy + NMES group performed 60 min of NMES in addition to 20 min of exercise therapy. For NMES, electrodes were placed at the motor points of RF and GAS on both legs, and both muscles were stimulated using an electrical stimulator (Intelect® Mobile Stim; Chattanooga®, Dallas, TX, USA) at a stimulation frequency of 100 Hz, a pulse width of 200 μs, and an on–off time of 10 s:10 s. A pulse current (average 32 mA) was applied to induce visible muscle contractions without causing pain or discomfort. Electrode placement sites were marked with a skin marker to ensure consistent stimulation locations each day. During the 60-min NMES session, patients were instructed to perform voluntary contractions at 60% of MVC in synchrony with the stimulation and completed a total of 180 repetitions of knee extension and ankle plantar flexion.
The 20-min exercise therapy consisted of range-of-motion exercises and strength training targeting the hip, knee, and ankle muscles, similar to the exercise therapy group protocol. Patients completed 20 repetitions each of knee extension and ankle plantar flexion, resulting in a total of 200 repetitions, consistent with the exercise therapy group.
Outcome Measures
All outcomes, except for functional mobility, were assessed preintervention and approximately 9 h postintervention. Beyond the outcome measures described in the following sections, the age, height, and weight of each patient were collected, and body mass index was calculated before the intervention.
Muscle Thickness and Echo Intensity
Muscle echo intensity was assessed as an indicator of intramuscular fat (23), with decreases in echo intensity reflective of reductions in intramuscular fat. Transversal B-mode images of RF and GAS on the dominant side were obtained using an ultrasound imaging diagnostic device (CX50; Philips Electronics, Amsterdam, the Netherlands), with an 8 MHz ultrasound probe (L12-3; Philips Electronics). The general gain was set at 45 dB, and the image depth was adjusted to 60 mm to visualize the entire muscle thickness in all the patients. The probe was positioned perpendicular to the muscle at 50% of the thigh length (between the anterosuperior iliac spine and the superior edge of the patella) for RF and at 30% of the lower-leg length measured from the inferior end of the fibular head (with the distance from the inferior end of the fibular head to the lateral malleolus defined as 100%) (24).
Before measurement, patients removed their underwear to fully expose the measurement sites and rested in a supine position with their lower limbs extended and relaxed for 15 min to allow stabilization of fluid shifts. A sufficient amount of ultrasound gel was used to minimize the pressure applied to the skin and enhance the image quality. All measurements were performed by the same operator with 4 yr of experience in ultrasound assessments (A.H.).
ImageJ image analysis software (National Institutes of Health, Bethesda, MD, USA) was used to determine the muscle thickness and echo intensity (25). For each muscle, a region of interest was selected to include as much muscle as possible while avoiding other tissues, such as bone and the surrounding fascia, for the echo intensity calculation. Muscle thickness was calculated as the distance between the periosteum and the fascia. Echo intensity was determined using the 8-bit gray-scale analysis function and expressed in arbitrary units as a value between 0 (black) and 255 (white). Two images were analyzed for muscle thickness and muscle echo intensity, and the average values were used for subsequent analysis.
Muscle Strength
Maximum knee extensor (RF) and ankle plantar flexor (GAS) strengths during isometric contraction of the dominant side were evaluated using a manual dynamometer (Moby, MT-100). All the participants performed two trials for each muscle and the highest value was recorded as the maximum muscle strength. Force was expressed in kilogram-force (kgf), which is the force exerted by a 1-kg mass under standard gravity (9.80665 m·s−²).
Circumference
The circumferences of the thigh and the calf were measured using a nonelastic graduated measuring tape in 0.1 cm increments. To enhance measurement accuracy, skin markings were applied before each measurement. The circumference of the thigh was measured at a site 15 cm above the superior border of the patella, and the calf was measured at 30% of the lower-leg length (the distance from the inferior end of the fibular head [0%] to the lateral malleolus [100%]) (24).
Functional Mobility
Functional mobility was assessed postintervention only using the timed up-and-go (TUG) test. During this test, participants were instructed to sit in a standard chair (seat height: 45 cm), stand up, walk 3 m at a comfortable but maximal pace, turn around an obstacle, and return to sitting in the chair (26).
Cognitive Function and Pain
Cognitive function was assessed using the Hasegawa Dementia Rating Scale-Revised (HDS-R, cutoff score of 20) (27). According to the inclusion criteria, all patients who were able to understand the exercise instructions were included in this study, even if the HDS-R score at enrollment was 20. Pain intensity was also evaluated at the time of admission using an 11-point numerical rating scale, where 0 indicates no pain and 10 indicates the worst imaginable pain.
Statistical Analysis
The Shapiro–Wilk test was used to assess the normality of the data, with a significance level of 0.05 as the criterion. The variables of interest were reported as mean ± standard deviation. The primary outcomes were RF and GAS muscle thickness. Secondary outcomes (echo intensity, muscle strength, circumference, and functional mobility [TUG]) were analyzed as confirmatory secondary/exploratory endpoints and interpreted cautiously. A two-way repeated-measures ANOVA tested group × time interactions for each outcome; where appropriate, Bonferroni-adjusted post-hoc pairwise comparisons were performed within factors. For the between-group comparison of TUG postintervention, an independent t test was used. Statistical significance was set at P < 0.05 (two-sided). Only measurements associated with the dominant leg of a patient were used in the statistical analysis. All statistical analyses were performed using SPSS Statistics, version 24 (IBM Corp., Armonk, NY, USA).
RESULTS
Patient Characteristics
None of the 20 participants dropped out of the study. Baseline anthropometric, cognitive, and pain measurements are presented in Table 1. No significant differences were observed between the exercise therapy group and exercise therapy + NMES group for any of the baseline characteristics.
Table 1 - Patient Characteristics Preintervention.
| | Exercise Therapy Group (n = 10) | Exercise Therapy+ NMES Group (n = 10) | P Value | | | ------------------------------------ | ---------------------------------------- | ----------- | ---- | | Age, yr | 80.9 ± 6.2 | 85.1 ± 5.7 | 0.15 | | Height, cm | 150.8 ± 7.2 | 147.2 ± 6.4 | 0.26 | | Weight, kg | 47.4 ± 9.5 | 45.9 ± 10.2 | 0.75 | | BMI, kg·m−2 | 20.8 ± 4.0 | 21.4 ± 5.2 | 0.77 | | HDS-R | 21.8 ± 3.2 | 24.6 ± 3.6 | 0.14 | | NRS | 7.6 ± 2.5 | 8.1 ± 1.7 | 0.77 |
Values are mean ± standard deviation.
BMI, body mass index; HDS-R, Hasegawa Dementia Rating Scale-Revised; NMES, neuromuscular electrical stimulation; NRS, numerical rating scale.
Muscle Thickness
A significant group × time interaction was observed for muscle thickness in both RF (F(1,18) = 4.2, P < 0.05, partial _η_2 = 0.22) and GAS (F(1,18) = 25.9, P < 0.001, partial _η_2 = 0.51). In the exercise therapy group, a significant decrease was observed in RF postintervention (−9.1%, P = 0.0006, 95% confidence interval [CI] = 0.11–0.28) (Table 2 and Fig. 2). Similarly, the muscle thickness of GAS significantly decreased from preintervention (−12.5%, P = 0.004, 95% CI = 0.06–0.21). In contrast, the exercise therapy + NMES group showed significant increases in muscle thickness for both RF (+30.0%, P = 0.0004, 95% CI = 0.17–0.42) and GAS (+50%, P = 0.0002, 95% CI = 0.21–0.47) following the intervention.
Table 2 - Outcome Measures Pre- and Postintervention.
| | Exercise Therapy Group (n = 10) | Exercise Therapy + NMES Group (n = 10) | | | | | ------------------------------------ | ----------------------------------------- | --------------------- | ---------------- | -------------------- | | | Preintervention | Postintervention | Preintervention | Postintervention | | | Muscle thickness | | | | | | RF, cm | 1.068 ± 0.343 | 0.870 ± 0.283* | 1.041 ± 0.360 | 1.339 ± 0.311* | | GAS, cm | 0.794 ± 0.164 | 0.662 ± 0.162** | 0.837 ± 0.172 | 1.178 ± 0.160* | | Echo intensity | | | | | | RF, pixel | 64.551 ± 11.552 | 80.101 ± 20.838*** | 65.363 ± 11.957 | 54.568 ± 9.545** | | GAS, pixel | 65.530 ± 19.099 | 86.863 ± 19.866** | 68.027 ± 11.530 | 58.627 ± 7.461*** | | Muscle strength | | | | | | RF, kgf·kg−1 | 0.093 ± 0.055 | 0.081 ± 0.050** | 0.081 ± 0.031 | 0.186 ± 0.077* | | GAS, kgf·kg−1 | 0.141 ± 0.058 | 0.110 ± 0.056*** | 0.135 ± 0.050 | 0.256 ± 0.068* | | Circumference | | | | | | RF, cm | 38.20 ± 6.505 | 37.55 ± 6.540 | 38.70 ± 6.420 | 39.0 ± 6.504 | | GAS, cm | 29.45 ± 3.539 | 28.75 ± 3.642*** | 28.20 ± 3.964 | 28.40 ± 3.754 | | Functional mobility | | | | | | TUG, s | - | 19.2 ± 5.4 | - | 12.6 ± 2.6**** |
Values are mean ± standard deviation. n = 10 per group.
*P < 0.001 vs preintervention.
**P < 0.005 vs preintervention.
***P < 0.05 vs preintervention (within-group).
****P < 0.005 vs exercise therapy group.
GAS, gastrocnemius; NMES, neuromuscular electrical stimulation; RF, rectus femoris; TUG, timed up-and-go test.
Effects of exercise with or without neuromuscular electrical stimulation (NMES) on muscle thickness (A), echo intensity (B), muscle strength (C), and circumference (D) during 1 wk of bed rest in older inpatients. Top row = rectus femoris (RF), bottom row = gastrocnemius (GAS). For all graphs, n = 10 per group. Values are shown as mean (bars) ± standard deviations (whiskers). Circles indicate individual data points. *P < 0.05 vs preintervention (within-group). **P < 0.01 vs preintervention. †† P < 0.01 vs postintervention in exercise therapy group.
Echo Intensity
There was a significant main effect and a significant group × time interaction for echo intensity for RF (F(1,18) = 6.9, P < 0.05, partial _η_2 = 0.16), whereas GAS showed an interaction without a significant main effect (F(1,18) = 3.3, P = 0.08, partial _η_2 = 0.29). In the exercise therapy group, echo intensity significantly increased postintervention for RF (+24.0%, P = 0.008, 95% CI = 5.11–25.99) (Fig. 2) and GAS (+32.7%, P = 0.001, 95% CI = 10.72–31.95). Conversely, in the exercise therapy + NMES group, echo intensity significantly decreased from preintervention in both RF (−16.5%, P = 0.001, 95% CI = 5.37–16.22) and GAS (−13.8%, P = 0.02, 95% CI = 3.79–17.4).
Muscle Strength
A significant main effect and a significant group × time interaction were observed for both RF (F(1,18) = 6.3, P < 0.05, partial _η_2 = 0.26) and GAS (F(1,18) = 12.9, P < 0.001, partial _η_2 = 0.26). In the exercise therapy group, muscle strength decreased postintervention in RF (−11.1%, P = 0.009, 95% CI = 0.01–0.03) (Fig. 2) and GAS (−21.4%, P = 0.04, 95% CI = 0.01–0.05). In contrast, the exercise therapy + NMES group showed significant improvements in muscle strength for RF (+137.5%, P = 0.0006, 95% CI = 0.06–0.15) and GAS (+100%, P = 0.0001, 95% CI = 0.07–0.16) compared with preintervention.
Circumference
No significant main effects or group × time interactions were observed between the exercise therapy group and the exercise therapy + NMES group for RF (F(1,18) = 0.2, P = 0.66, partial _η_2 = 0.001) or GAS (F(1,18) = 0.4, P = 0.52, partial _η_2 = 0.007). In the exercise therapy group, RF circumference did not change postintervention (−1.57%, P = 0.41, 95% CI = 0.52–1.38) (Fig. 2), whereas GAS circumference decreased (−2.37%, P <0.03, 95% CI = 0.24–1.36). In the exercise therapy + NMES group, neither RF (+0.77%, P = 0.46, 95% CI = 0.16–1.24) nor GAS (+0.71%, P = 0.45, 95% CI = 0.35–1.05) showed a significant change in circumference postintervention.
Functional Mobility
Postintervention, the exercise therapy + NMES group exhibited significantly shorter TUG times than the exercise therapy group (12.6 ± 2.6 s vs 19.2 ± 5.4 s, P < 0.005) (Table 2).
DISCUSSION
This study investigated whether a combination of NMES and exercise therapy can prevent the muscle atrophy and weakness induced by 1 wk of bed rest in older female inpatients. Participants received either exercise therapy alone or a combination of NMES and exercise therapy daily during the bed-rest period. We found that the combination of NMES and exercise therapy prevented muscle atrophy and weakness and deterioration in muscle quality, which could not be achieved by exercise therapy alone.
Impact on Muscle Thickness
Our study revealed that the muscle thickness of the lower limb decreased after 1 wk of bed rest despite daily exercise therapy. A previous study in an intensive care unit population showed that decreases in muscle thickness of the RF muscle progressed despite patients having undergone exercise therapy within the first 2 wk of admission (28). Other studies similarly demonstrated that thigh muscle cross-sectional area decreased even when exercise therapy was initiated early following intensive care unit admission in critically ill patients (29,30). Moreover, in older patients requiring bed rest—like those in the present study—muscle atrophy is readily induced due to age-related sarcopenia, the predominance of fast-fiber atrophy with aging, and additional slow-fiber atrophy under disuse conditions (31). In such patients, maintaining muscle mass with exercise therapy alone is challenging because sufficient active skeletal muscle loading is difficult to achieve (32).
In this study, the combination of NMES and exercise therapy not only prevented muscle atrophy but also enhanced muscle thickness. During voluntary contractions, motor units are typically recruited in accordance with the size principle: under higher loads (approximately ≥60% of MVC), lower-threshold, fatigue-resistant slow-twitch fibers are activated first, followed by high-threshold fast-twitch fibers (33,34). NMES, however, can depolarize peripheral motor axons beneath the stimulation electrodes and thereby recruit motor units in a pattern that may bypass conventional orderly recruitment, enabling activation of both slow- and fast-twitch fibers within the stimulated region (33). Previous studies examining muscle fiber distribution and recruitment characteristics indicate that superficial regions of lower-limb musculature tend to contain a greater proportion of fast-twitch fibers, whereas deeper regions are relatively slow-twitch fiber dominant (35). Overall, these observations suggest that NMES, compared with voluntary contractions, may be better at engaging fast-twitch muscle fibers under low-to-moderate loading, thereby facilitating increases in muscle thickness. Although additional studies are needed to elucidate the precise mechanisms driving early-phase hypertrophic responses to NMES, our results indicate that the inclusion of NMES in an exercise therapy regimen may greatly contribute to preventing bed-rest-induced muscle atrophy in older inpatients.
Impact on Echo Intensity
Echo intensity decreased significantly in the exercise therapy + NMES group postintervention for both RF and GAS. Echo intensity reflects intramuscular fat (23); therefore, a reduction in echo intensity implies decreased intramuscular fat and improvements in muscle quality. Even a short period of bed rest (~1 wk) reduces skeletal muscle glucose uptake and increases insulin resistance (36), which in turn can increase intramuscular fat mass (37). Previous studies have shown that approximately 1 wk of NMES increases oxygen consumption to about twice resting levels and improves insulin resistance by elevating energy expenditure (38). Moreover, exercise therapy combined with NMES improved insulin resistance more than either exercise therapy or NMES alone (39). Overall, these findings suggest that combining exercise therapy with NMES may counter insulin resistance, thereby reducing intramuscular fat mass, although the mechanisms underlying this outcome were not directly assessed in the present study.
Impact on the Muscle Strength
Combining exercise therapy and NMES significantly increased RF and GAS muscle strength and thickness. Maximum muscle strength is calculated as muscle cross-sectional area × absolute muscle strength, with increases in muscle strength caused by increases in either or both muscle cross-sectional area and absolute muscle strength (40). In general, muscle strength increases due to neurological adaptations in the early phases of resistance training and then morphological factors, such as hypertrophy, gradually dominate after 3–5 wk of resistance training (41,42). Based on previous findings, the increase in muscle strength in our study was assumed to be primarily attributable to neurological factors because the intervention period was only 1 wk. However, an increase in muscle thickness, which is highly correlated with the muscle cross-sectional area, was also observed in the exercise therapy + NMES group, indicating that both neural and morphological factors contributed to the increase in muscle strength. To further explore these mechanisms, it would be beneficial to conduct a direct assessment of muscle activation. Due to NMES being capable of depolarizing peripheral motor axons, this approach could drive a substantial neural contribution to the observed gains in strength. Electromyography-based assessments have shown neuromuscular junction function and the efficiency of neural transmission to be strongly coupled with muscle strength (43,44). However, because electromyography was not performed in the present study, the relative contributions of neural versus morphological factors could not be determined.
Impact on Circumference
In the exercise therapy group, RF circumference did not change, whereas GAS circumference decreased significantly. In the exercise therapy + NMES group, increases in RF and GAS circumferences were not detected, yielding results incongruent with the increase in muscle thickness observed via ultrasound. Ultrasonography provides superior tissue specificity and higher spatial resolution (≈0.2 mm) (45), whereas tape-based circumference measurements yield variable outcomes due to various factors (e.g., human error, variability in limb positioning during measurement, and variability in tape tension). Moreover, the ultrasound-observed changes in muscle thickness were negligible (≈0.1–0.3 cm); such localized alterations were likely below the detection threshold of circumference measurements—a composite metric (muscle, subcutaneous tissue, and fluid) typically recorded in 0.5-cm increments. Accordingly, these measurement variables, combined with the small, localized changes in muscle thickness, likely account for the discrepancy between circumference and ultrasound findings.
Impact on Functional Mobility
Combining exercise therapy with NMES improved functional mobility in the current study. Postintervention, the exercise therapy + NMES group had significantly faster TUG performance than the exercise therapy group. The TUG test provides a composite index of functional mobility by integrating lower-limb strength, balance, and coordination across tasks such as standing up, walking, turning, and sitting down (46). Accordingly, the faster TUG times in the exercise therapy + NMES group suggest that the intervention not only preserved muscle mass and strength but also improved performance on complex functional tasks. These findings show that the combined intervention facilitated more rapid recovery of mobility—encompassing standing, ambulation, and balance—and may be particularly beneficial for older adults during short-term bed rest.
Comparison With Previous Studies
Our findings highlight significant preservation and even augmentation of muscle mass and strength with the combination of NMES and exercise therapy during short-term bed rest. Our results are consistent with those of previously published literature, which has shown the efficaciousness of NMES in mitigating muscle atrophy across various clinical populations (47). For example, NMES has been shown to prevent muscle atrophy in severely ill patients, highlighting its potential as an alternative to voluntary exercise when patient effort is limited (48).
Nevertheless, some studies have reported more modest or inconsistent effects of NMES on muscle hypertrophy and strength. Specifically, although NMES can improve strength, the hypertrophic response in healthy individuals is often smaller than that achieved with voluntary resistance training (49). Such discrepancies may be attributable to differences in stimulation intensity, frequency, and duration, as well as whether NMES is combined with voluntary exercise.
Notably, the intervention period in the present study was only 1 wk, a period shorter than that of most previous NMES studies (47). Despite the inherent brevity of our intervention, our results indicate that combining NMES with exercise can produce substantial improvements in muscle mass and strength in frail older adults, a population often considered less responsive to hypertrophic stimuli. This suggests that NMES may enhance neuromuscular activation and recruitment patterns beyond voluntary efforts alone, particularly in individuals with a limited capacity for active exercise (50). Furthermore, our combined intervention yielded clinically meaningful functional gains, as evidenced by faster TUG performance. Overall, these findings support and extend the results of Paillard et al (47), who reported improvements in muscle strength and activities of daily living with NMES, outcomes that ultimately improved the quality of life of the participants.
Limitations
This study has several limitations. First, the generalizability of our findings may be limited because participants were relatively independent and able to stand before hospitalization, which may not reflect the broader population of bedridden older adults. Nevertheless, high adherence in the NMES group, even among individuals with higher pain levels, suggests that the intervention is feasible for inpatients with limited mobility or motivation. Second, intramuscular edema associated with short-term bed rest may have influenced imaging-based estimates of muscle size (e.g., apparent increases in thickness) due to altered vascular permeability and fluid shifts (51). Third, the modest sample size (n = 20) restricts the detection of small effects and subgroup differences, so the impact of Type II errors cannot be ruled out entirely. Fourth, functional mobility (TUG) was assessed postintervention only and HDS-R and anthropometric measures were collected preintervention only; together, these constraints precluded within-subject change analyses and limited inference about trajectories. Finally, this was a single-center study of female older inpatients; therefore, setting- and sex-specific factors may constrain external validity. Future studies with larger, more diverse cohorts, longitudinal functional assessments, and mechanistic measures (e.g., electromyography and magnetic resonance imaging) will be necessary to confirm and extend these findings.
Conclusions
Our findings show that combining NMES with exercise therapy during the first week of hospitalization can prevent muscle atrophy and weakness while increasing muscle mass and strength in older inpatients. This combined intervention also culminated in faster TUG performances, indicating benefits for functional mobility. These findings suggest that this combined approach may be an effective intervention for patients who are bedridden or have limited mobility due to pain. Future studies should evaluate longer-term outcomes, including activities of daily living and post-bed-rest functional recovery.
ACKNOWLEDGMENTS
The authors would like to thank the individuals who participated in this study. The results of the present study do not constitute endorsement by the American College of Sports Medicine.
CONFLICTS OF INTEREST AND SOURCE OF FUNDING
The authors have no conflicts of interest or funding sources to report.
DATA AVAILABILITY
All data generated and/or analyzed during the current study are not publicly available due to participant consent limitations but will be made available by the corresponding author upon reasonable request.
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Keywords:
bed rest; electric stimulation therapy; exercise therapy; muscle atrophy; older adults; ultrasound
Copyright © 2025 The Author(s). Published by Wolters Kluwer Health, Inc.