Muscular Torque Output During Neuromuscular Electrical Stimulation Following a 4-week Training Intervention in Older Adults

Neuromuscular electrical stimulation (NMES) can be used to induce muscle torque by generating involuntary muscle contractions. If a greater muscular torque and torque maintenance could be induced by NMES training bouts, it may lead to improvements in electrically induced muscular endurance. However, little is known regarding torque output during NMES pre-post training. PURPOSE: The purpose of this study was to determine if a 4-week NMES training intervention would alter involuntary muscular torque output during the NMES protocol in older, healthy adults. METHODS: Eleven older adults (68.7 ± 2.1 years) completed 12 (Day 1 – Day 12), 40-min NMES training sessions of the quadriceps muscles three times a week, over 4-weeks, with the stimulation frequency set at 60 Hz. Maximal voluntary contractions (MVC) were measured pre-training and mid-training. NMES was delivered through stimulation electrodes placed on the quadriceps muscles and torque output was recorded during the training sessions. Stimulation intensity was set to generate muscular torque output to meet a target representing 15% MVC and was adjusted every 5 minutes to achieve target torque. During each training session, 96 total contractions were generated during the NMES protocol. For Day 1 and Day 12, mean torque, peak torque, and torque time integral (TTI) were measured for each contraction and were then normalized to the pre-training MVC for Day 1 and mid-training MVC for Day 12. The overall mean of the 96 contractions was then calculated for each torque parameter. Sum of TTI (STTI) was calculated by summing the normalized TTI for all contractions. The average stimulation intensity was recorded, and the mean was calculated for each day. Paired sample t-tests were used to test for differences between Days (Day 1 and Day 12) for torque parameters and stimulation intensity. Statistical significance was set at p ≤ 0.05. RESULTS: TTI (Day 1: 90.5 ± 6.1% MVC vs Day 12: 75.9 ± 9.4% MVC; p = 0.036) and STTI (Day 1: 8,686.4 ± 582.0% MVC vs Day 12: 7,2801.0 ± 903.8% MVC; p = 0.036) were lower on Day 12 compared to Day 1. Additionally, there was a trend toward lower mean torque after training (Day 1: 8.7 ± 0.5% MVC vs Day 12: 7.3 ± 0.9% MVC; p = 0.055). Peak torque was not different between days (Day 1: 12.9 ± 0.6% MVC vs Day 12: 13.0 ± 0.7% MVC; p = 0.859). Stimulation intensity showed a trend toward higher stimulation intensity on Day 12 compared to Day 1 (Day 1: 13.3 ± 0.7 mA vs Day 12: 14.6 ± 1.0 mA, p = 0.10). CONCLUSION: Torque output during the NMES protocol was not improved with NMES training and demonstrated a decrease in some torque parameters. The inability of the muscle to produce similar torque output after training may be due to muscle accommodation to the NMES stimulation with repeated bouts. If the goal is to improve involuntary muscular endurance, allowing for more recovery between NMES sessions and use of a lower stimulation frequency may facilitate greater overall muscular torque output following NMES training

Changes in Physical Function Following 4-Weeks of Neuromuscular Electrical Stimulation Training in Older Adults

Sarcopenia, the age-related loss of muscle mass and strength, can result in a decline in physical function. Neuromuscular electrical stimulation (NMES) has been shown to induce muscular adaptations that have the potential to translate to functional improvements; however, little is known regarding functional adaptations pre-post short-term NMES training, especially in older adults. PURPOSE: The aim of this study was to determine NMES-induced changes in lower extremity physical function following 4 weeks of an NMES training intervention of the quadriceps muscle in older adults. METHODS: Seventeen healthy, older adults (68.8 ± 1.8 years old) were divided into two groups: NMES (n = 12) and SHAM (n = 5). The NMES group underwent 12, 40-minute NMES training sessions to the quadriceps muscles on each leg 3x/week over 4 weeks, with the stimulation intensity adjusted every 5 minutes, as needed, to achieve a 15% target torque of each participant’s maximal voluntary contraction (MVC). The stimulation parameters consisted of a 60 Hz stimulation frequency and a duty cycle of 10s on and 15s off. The SHAM group was blinded and did not receive any treatment. The following functional assessments were measured before and after the 4-week training period: Timed Up and Go (TUG), 5x Sit-to-Stand (5XSTS), Stair Climb (SC), and 6-Minute Walk Test (6MWT). Repeated-measures ANOVAs were used to determine changes in TUG, 5XSTS, SC, and 6MWT assessments pre-post NMES training and data are reported as mean ± SE. Statistical significance was set at P \u3c 0.05. RESULTS: NMES training significantly improved TUG (NMES: 8.81 ± 0.54s vs. 7.67 ± 0.39s; P = 0.002; SHAM: 10.60 ± 2.41 vs. 10.93 ± 3.01s; P = 0.652; pre- and post-training, respectively) and SC (NMES: 4.03 ± 0.20s vs. 3.76 ± 0.16s; P = 0.023; SHAM: 6.53 ± 2.11 vs. 6.0 ± 1.78s; P = 0.215; pre- and post-training, respectively); however, 5XSTS (NMES: 9.70 ± 0.75 vs. 8.83 ± 0.72; P \u3e 0.05; SHAM: 14.34 ± 3.64 vs. 13.28 ± 3.89; P \u3e 0.05; pre- and post-training, respectively) and 6MWT (NMES: 610.10 ± 22.68 vs. 623.74 ± 14.73; P \u3e 0.05; SHAM: 533.43 ± 82.44 vs. 587.81 ± 80.52; P \u3e 0.05; pre- and post-training, respectively) did not change following the NMES intervention. CONCLUSION: Improvements in TUG and SC following 4 weeks of NMES training demonstrate augmented lower body physical function, suggesting that short-term NMES training programs may induce neuromuscular adaptations that contribute to these early improvements in physical function in older adults

Neuromuscular Electrical Stimulation Effects on Skeletal Muscle Fatigue in Older Adults

Neuromuscular electrical stimulation (NMES) is often used as a rehabilitative modality and evidence has suggested that high frequencies of NMES may elicit increases in muscle strength. However, little is known regarding the effects of a high-frequency NMES intervention on voluntary skeletal muscle fatigue. PURPOSE: The aim of this study was to determine the effect of a 4-week high-frequency NMES intervention on voluntary muscular fatigue and changes in neuromuscular activation patterns of the quadriceps during voluntary fatiguing muscle contractions in older adults. METHODS: Seventeen healthy, older adults (68.8 ± 1.8 years old) participated in the study (NMES: n = 12; SHAM: n = 5). Each participant was seated on an isokinetic dynamometer, and a 40-min NMES treatment was applied to the quadriceps muscles of each leg 3x/week for 4 weeks with the stimulation frequency set at 60 Hz. Stimulation intensity was set to achieve 15% of knee extension maximal voluntary contraction (MVC). Those in the SHAM group underwent the same treatment procedures but did not receive the NMES treatment. All subjects performed maximal voluntary contractions (MVC) and an intermittent knee extension isometric submaximal voluntary fatigue task at 50% MVC until the fatigue criteria were met for pre-post testing. Surface electromyography (sEMG) of the vastus lateralis (VL) and vastus medialis (VM) muscles were recorded during the fatigue task to examine changes in muscle activation. EMG data were quantified for root mean square (RMS) EMG and reported as a percent rate of change over the duration of the fatigue task and median frequency (MF) is reported as the average MF during the fatigue task. Repeated measures ANOVAs were used to determine differences pre-post NMES for muscular endurance time, MVC and EMG measures. Statistical significance was set at p \u3c 0.05. RESULTS: MVC increased pre-post NMES in the NMES group (117.1 ± 8.7 Nm vs 127.6 ± 11.1 Nm, p = 0.049; pre- and post-training, respectively) with no change in SHAM (p = 0.96). Muscular endurance time did not change pre-post NMES (NMES: 159.3 ± 20.1s vs 141.9 ± 21.2s, p = 0.29; SHAM: 242.2 ± 43.3s vs 202.9 ± 23.3s, p = 0.13; pre- and post-training, respectively). RMS EMG rate of change did not change following NMES treatment (NMES: VL: 16.6 ± 3.6% vs 18.8 ± 10.4%, p = 0.84; VM: 11.4 ± 2.1% vs 19.6 ± 5.5%, p = 0.15; SHAM: VL: 7.8 ± 1.6% vs 7.1 ± 3.0%, p = 0.81; VM: 7.1 ± 3.3% vs 5.9 ± 2.2%, p = 0.55; pre- and post-training, respectively). Also, there was no difference in MF EMG with NMES training (NMES: VL: 77.6 ± 4.1 Hz vs 74.9 ± 3.6 Hz, p = 0.13; VM: 72.5 ± 2.4 Hz vs 72.6 ± 2.2 Hz, p = 0.97; SHAM: VL: 79.3 ± 3.4 Hz vs 80.2 ± 4.9 Hz, p = 0.85; VM: 76.9 ± 3.7 Hz vs 83.9 ± 5.1 Hz, p = 0.12; pre- and post-training, respectively). CONCLUSION: Treatment with high-frequency NMES did not improve muscle endurance or related EMG parameters. It is possible that NMES induced adaptations may be frequency-specific and that high-frequency NMES may not be efficacious when the goal is to improve skeletal muscle endurance

Improvement in Physical Function and Quality of Life in Older Adults Following 4 Weeks of Neuromuscular Electrical Stimulation

Older adults often suffer from sarcopenia, the age-related loss of muscle mass and strength, which negatively impacts physical function and quality of life (QoL). Neuromuscular electrical stimulation (NMES) is frequently used in physical rehabilitation as a muscle strengthening modality; however, little research exists on QoL outcomes in response to NMES. PURPOSE: The aim of this study was to determine changes in QoL and physical function in older adults after 4 weeks of NMES. METHODS: Ten healthy, older adults participated in the study (67.8 ± 2.1 years-old). Each participant was seated on an isokinetic dynamometer with the knee positioned at 60°, and a 40-min NMES treatment was applied to the quadriceps muscles of each leg 3 times per week for 4 weeks. Stimulation frequency was set at 60 Hz with repeated cycles of 10s on and 15s off. Stimulation intensity was set to achieve 15% of each participant’s maximal voluntary contraction (MVC) and was increased every 5 minutes if the torque was below 15% MVC. Each subject was given a pre and post intervention survey assessing indicators of QoL: self-efficacy for physical function (0-100 scale), perceived competence in physical domains (e.g., strength, endurance, coordination, 1-6 scale), physical self-concept (1-6 scale), and intention to be physically active (1-7 scale). Physical function of the lower body was assessed pre and post intervention with a timed up and go test (TUG). Paired sample t-tests were used to test for differences over time (pre, post) for TUG and QoL dimensions (significance set at p \u3c 0.05). Cohen’s d was calculated for effect size. RESULTS: Perceived coordination significantly increased with a medium effect size (5.10 ± .0.16 vs 5.38 ± 0.17, p = 0.03, d = 0.55), pre vs post, respectively. The following QoL dimensions showed a statistically non-significant increase with a small effect size: intention to be physically active (6.08 ± 0.58 vs 6.68 ± 0.22, p = 0.33, d = 0.48), self-efficacy (95.61 ± 2.19 vs 97.37 ± 1.40, p = 0.10, d = 0.31), and endurance (3.57 ± 0.33 vs 3.77 ± 0.19, p = 0.43, d = 0.24). Two dimensions trended toward improvement: physical self-concept (4.57 ± 0.35 vs 4.77 ± 0.30, p = 0.37, d = 0.19) and physical activity (4.08 ± 0.45 vs 4.30 ± 0.31, p = 0.36, d = 0.19. There was a significant decrease in time to complete the TUG (8.77 ± 0.59s vs 7.71 ± 0.43s, p = 0.004, d = 0.63). CONCLUSION: TUG times and coordination showed significant improvement while other QoL dimensions trended toward improvement after 4 weeks of NMES. Enhanced physical function subsequent to NMES treatment may contribute to improved overall QoL by increasing confidence to perform physical activities, and may thereby counter the risk of sarcopenia

Effect of Neuromuscular Electrical Stimulation Training on Control of Involuntary Muscular Torque and Stimulation Intensity in Older Adults

International Journal of Exercise Science 16(3): 482-496, 2023. The purpose of this study was to examine the effects of a 4-week neuromuscular electrical stimulation (NMES) training regimen on involuntary torque output and electrical stimulation intensity in older adults. Twelve older adults (ages: 68.4 ± 6.5 years; men: n = 6, women: n = 6; weight: 158.6 ± 27.3 lbs; height: 65.2 ± 2.1 in) received submaximal intensity NMES to the quadriceps for 4 weeks to determine training-related changes in stimulation intensity and involuntary control of muscular torque during the NMES protocol. Two-way repeated measures ANOVAs were used to compare torque parameters and stimulation intensity between days and across protocol time bins. After training, stimulation intensity and torque increased over the course of the NMES protocol, while torque decreased during the protocol pre-training. These results suggest that muscular endurance of involuntary muscle contraction is increased with NMES training, and that stimulation intensity should be increased throughout the course of training to augment muscular torque output

Acute Supplementation with Cannabidiol Does Not Attenuate Inflammation or Improve Measures of Performance following Strenuous Exercise

Supplementation with cannabidiol (CBD) may expedite recovery when consumed after exercise. The purpose of this study was to determine if supplementation with CBD reduces inflammation and enhances performance following strenuous eccentric exercise in collegiate athletes. Twenty-four well-trained females (age = 21.2 ± 1.8 years, height = 166.4 ± 8 cm, weight = 64.9 ± 9.1 kg) completed 100 repetitions of unilateral eccentric leg extension to induce muscle damage. In this crossover design, participants were randomized to receive 5 mg/kg of CBD in pill form or a placebo 2 h prior to, immediately following, and 10 h following muscle damage. Blood was collected, and performance and fatigue were measured prior to, and 4 h, 24 h, and 48 h following the muscle damage. Approximately 28 days separated treatment administration to control for the menstrual cycle. No significant differences were observed between the treatments for inflammation, muscle damage, or subjective fatigue. Peak torque at 60°/s (p = 0.001) and peak isometric torque (p = 0.02) were significantly lower 24 h following muscle damage, but no difference in performance was observed between treatments at any timepoint. Cannabidiol supplementation was unable to reduce fatigue, limit inflammation, or restore performance in well-trained female athletes