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

Predicting Resting Metabolic Rate in Healthy Adults using Body Composition and Circumference Measurements

Measurement of resting metabolic rate (RMR) is an important factor for weight management. Previous research has reported several variables to estimate RMR such as body size, percent fat (%BF), age, and sex; however, little is known regarding the effect of circumference measures in estimating RMR. PURPOSE: The purpose of this study was to develop a model to estimate RMR using waist circumference (WC), an easily obtainable measure, and cross-validate it to previously published models. METHODS:Subjects were 140 adult men and women, ages 18-65 years. RMR was measured through indirect calorimetry, %BF was measured through air displacement plethysmography, and fat mass and fat-free mass were determined from %BF and weight. Other variables collected were: weight, height, age, sex, ethnicity, body mass index, WC, hip circumference, waist-to-hip ratio, waist-to-height ratio, and %BF estimated from bioelectrical impedance analysis. Subjects were randomly divided into derivation and cross-validation samples. A multiple regression model was developed to determine the most accurate estimation of RMR in the derivation sample. The cross-validation sample was used to confirm the accuracy of the model and to compare the accuracy to published models. RESULTS:The best predictors for estimating RMR were body weight, r = 0.70, p= 0.031, age, r = -0.30, p= 0.012, and sex, r = 0.51, p= 0.018. Other factors failed to account for significant variation in the model. The derived equation for estimating RMR is: RMR (kcal/day) = 843.11 + 8.77(weight) – 4.23(age) + 228.54(sex, M = 1, F = 0), R2= 0.68, SEE = 173 kcal/day. Cross-validation statistics were: R2= 0.54, p £0.05, SEE = 199 kcal/day, and total error = 198 kcal/day. In published models, R2ranged from 0.47 to 0.57, SEE ranged from 192 to 213 kcal/day, and total error ranged from 212 to 1311 kcal/day. CONCLUSIONS:Cross-validation to published models for estimating RMR were similar to those of the derived model; however, the total error in the derived equation was lower than any of the previously published models. Several published models considerably overestimate RMR compared to the current model. The results of this study suggest that RMR can be reasonably estimated with easily obtainable measures which allow for estimation and implementation of RMR for weight management in clinical practice

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

Resistance Training and Quality of Life Among Younger and Older Adults

Older adults are at risk for sarcopenia, which can lead to reduced physical function, physical activity, and quality of life (QoL). PURPOSE: To determine the effects of aging and sedentary behavior on risk for sarcopenia, the purpose was to compare resistance trained and nonresistance trained younger and older adults on two sarcopenia-related outcomes: QoL and physical activity level (PA). METHODS: Younger (23.8 ± 0.4) and older (68.5 ± 1.2) healthy adults were categorized into 4 groups: young trained (YT: n = 22), young not trained (YNT: n = 16), old trained (OT: n = 17), and old not trained (ONT: n = 21). Resistance trained participants trained ≥ 2X per week, for the past ≥ 6 months. Participants completed a survey to assess health-related QoL, using the Sarcopenia and Quality of Life Questionnaire (SarQoL), and PA, using the Leisure Time Exercise Questionnaire (LTEQ). The SarQoL provides a total QoL score based on 7 dimensions. We were interested in total QoL and the following 3 dimensions: physical and mental health, functionality, and activities of daily living (ADLs). Scores range from 0 (worst health) to 100 (best health). The LTEQ provides a score for PA units, based on vigorous, moderate, and light PA in the past week, with higher scores indicating more PA. ANOVAs were used to determine group differences for each variable, p ≤ 0.05. Data are reported as mean ± SE. RESULTS: Group differences emerged for all variables (p ≤ 0.05). For total QoL, YT (94.5 ± 1.4) was significantly higher than all other groups (YNT: 86.4 ± 1.6, p \u3c 0.001; OT: 87.1 ± 1.6, p = 0.001; ONT: 81.9 ± 1.4, p \u3c 0.001). OT (p = 0.017) and YNT (p = 0.039) were significantly higher than ONT. For physical and mental health, YT (94.2 ± 2.4) was significantly higher than all groups (YNT: 82.2 ± 2.8, p = 0.002; OT: 85.8 ± 2.7, p = 0.022; ONT: 77.9 ± 2.4, p \u3c 0.001). OT was significantly higher than ONT (p = 0.035). For functionality (e.g., balance, climbing stairs), YT (97.5 ± 1.4) again was significantly higher than the other groups (YNT: 92.0 ± 1.6, p = 0.012; OT: 88.9 ± 1.6, p \u3c 0.001; ONT: 85.6 ± 1.4, p \u3c 0.001). YNT was significantly higher than ONT (p= 0.004). For ADLs (e.g., difficulty, fatigue, or pain during physical effort), YT (95.4 ± 1.7) was significantly higher than all groups (YNT: 87.3 ± 1.9, p = 0.002; OT: 87.9 ± 1.9, p = 0.004; ONT: 84.7 ± 1.7, p \u3c 0.001). For all QoL variables, OT did not differ from YNT (p \u3e 0.05). For PA, YT (58.5 ± 6.1 AU) had the same activity level as OT (50.0 ± 6.9 AU, p = 0.356). YT was significantly higher than YNT (31.1 ± 7.3 AU, p = 0.005) and ONT (32.4 ± 6.4 AU, p = 0.004). All other group comparisons were not different (p \u3e 0.05). CONCLUSION: Interestingly, OT was similar to YT on PA and similar to YNT on QoL outcomes. Further, OT was higher than ONT on perceptions of physical and mental health and total QoL. These data suggest that resistance training may be an effective modality to improve or maintain QoL as individuals age

Effects of Resistance Training Status on Exercise Patterns and Body Composition Among Younger and Older Adults

As individuals age, percent body fat tends to increase and lean muscle mass decreases, which may limit the ability to engage in higher intensity exercise. Moderate to vigorous physical activity has been shown to improve body composition, but it is unclear whether exercise patterns, such as amount of moderate and high intensity exercise performed, are impacted by resistance training status in younger and older adults. PURPOSE: To examine whether resistance trained and untrained younger and older adults differ on duration of high, moderate, and low intensity exercise and percent body fat (%BF). METHODS: Younger (23.8 ± 0.4 years) and older (68.5 ± 1.2 years) healthy adults were categorized into 4 groups based on resistance training status: young resistance trained (YT: n = 22), young not resistance trained (YNT: n = 16), old resistance trained (OT: n = 17), and old not resistance trained (ONT: n = 20). Resistance trained participants had been training ≥ 2X per week, for the past ≥ 6 months. Participants completed a survey to assess the intensity and duration of exercise, and a dual x-ray absorptiometry (DEXA) scan was used to determine %BF. The survey asked how many minutes/hours per week participants engaged in high intensity exercise (e.g., jogging, hiking), moderate intensity exercise (e.g., light bicycling, walking briskly), and low intensity exercise (e.g., slow walking, easy yoga). Responses were coded as 1 = none, 2 = 30-60 minutes, 3 = 1-2 hours, 4 = 2-3 hours, 5 = 3-5 hours, and 6 = more than 5 hours. ANOVAs were used to determine group differences for each variable, p ≤ 0.05. Data are reported as mean ± SE. RESULTS: Group differences emerged for high and moderate intensity exercise (p \u3c 0.05), but not for low intensity (p \u3e 0.05). For high intensity, YT (3.64 ± 0.31) was significantly higher than YNT and ONT (YNT: 1.63 ± 0.37, p \u3c 0.001; ONT: 1.55 ± 0.33, p \u3c 0.001), and OT (2.82 ± 0.36) was significantly higher than YNT and ONT (YNT: p = 0.022; ONT: p = 0.010). For moderate intensity, YT (4.91 ± 0.31) was significantly higher than YNT and ONT (YNT: 2.40 ± 0.38, p \u3c 0.001; ONT: 3.52 ± 0.32, p = 0.003), and OT (4.77 ± 0.35) was significantly greater than YNT and ONT (YNT: p \u3c 0.001; ONT: p = 0.011). Also for moderate intensity, ONT was significantly greater than YNT (p = 0.025). For %BF, YT (25.06 ± 2.1%) was significantly lower than YNT and ONT (YNT: 33.55 ± 1.87%, p = 0.001; ONT: 36.47 ± 1.28%, p \u3c 0.001), and OT (29.37 ± 1.11%) was significantly lower than ONT (p = 0.003). All other group comparisons were not different (p \u3e 0.05). CONCLUSION: The older resistance trained individuals did not differ from the younger trained participants on exercise patterns or percent body fat, suggesting the enduring positive effects of resistance training as individuals age. These resistance trained individuals also performed more moderate and high intensity exercise than non-resistance trained groups, likely contributing to their favorable body composition. Funded by Texas American College of Sports Medicine Student Research Development Award to H. Kendall, J. Mettler, and L. Kipp, and Thesis Fellowship Award to H. Kendall

Resistance Training may Mitigate Age-related Decline in Physical Function

Aging is often accompanied with the onset of sarcopenia, defined by low muscle mass, strength, and physical function. Regular resistance exercise may mitigate this loss; however, data are lacking that compare younger and older adults who do and do not perform resistance training for general health on skeletal muscle mass and physical function. PURPOSE: The aim of this study was to identify differences in muscle mass and physical function between younger and older adults who did and did not perform resistance training for general health. METHODS: Healthy younger (23.8 ± 0.4 yrs) and older (68.5 ± 1.2 yrs) men and women (n = 76) who either did or did not regularly participate in resistance training were placed into 4 groups: young trained (YT: n = 22), young not trained (YNT: n = 16), old trained (OT: n = 17), and old not trained (ONT: n = 21). Dual energy x-ray absorptiometry assessed appendicular skeletal muscle mass (SMI). Participants performed 4 physical function tests: stair climb (SC), 30s sit-to-stand (30sSTS), 6-min walk test (6MWT), and timed-up-and-go (TUG). ANOVAs were used to compare groups for all measures, p ≤ 0.05. Data are reported as mean ± SE. RESULTS: Differences were found between groups for SMI, SC, 30sSTS, 6MWT, and TUG (p ≤ 0.05). SMI was higher for YT compared to YNT (p = 0.001), ONT (p \u3c 0.0001) and OT (p = 0.032) (YT: 8.67 ± 0.36 kg/m2, YNT: 7.08 ± 0.23 kg/m2, OT: 7.73 ± 0.29 kg/m2, ONT: 7.11 ± 0.27 kg/m2). SC performance was slower for ONT compared to YT (p \u3c 0.0001), YNT (p \u3c 0.0001), and OT (p = 0.032); however, YT and was faster than OT (p = 0.002) (YT: 2.37 ± 0.05s, YNT: 2.60 ± 0.10s, OT: 2.94± 0.15s, ONT: 3.32 ± 0.16s). For 30sSTS, OT completed more reps than ONT (p \u3c 0.0001) and YNT (p = 0.001). YT completed more reps than YNT (p \u3c 0.0001) and ONT (p \u3c 0.0001) (YT: 22.8 ± 0.5 reps, YNT: 18.4 ± 0.7 reps, OT: 22.1 ± 1.1 reps, ONT: 16.7 ± 0.6 reps). OT (p = 0.001), YT (p \u3c 0.0001), and YNT (p = 0.046) walked farther in the 6MWT compared to ONT, and YT walked farther than YNT (p = 0.048) (YT: 837.0 ± 16.7 yds, YNT: 783.2 ± 14.5 yds, OT: 819.9 ± 23.3 yds, ONT: 728.3 ± 18.9 yds). For TUG, OT (p = 0.001) and YT (p = 0.046) were faster than ONT (YT: 5.81 ± 0.17s, YNT: 5.87 ± 0.25s, OT: 5.31 ± 0.19s, ONT: 6.35 ± 0.21s). 30sSTS, 6MWT and TUG were not different between OT and YT. 6MWT and SC were not different between OT and YNT (p \u3e 0.05). All other comparisons were not significantly different (p \u3e 0.05). CONCLUSION: Resistance trained older adults outperformed their nonresistance trained peers and these data suggest that older adults who engage in regular resistance training may maintain physical function similar to that of younger 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

Effects of Neuromuscular Electrical Stimulation Training on Skeletal Muscle Anabolic Signaling in Older Adults

Neuromuscular electrical stimulation (NMES) generates involuntary muscle contraction and may be a safe and effective alternative to voluntary resistance training, which is important for those who cannot perform voluntary exercise due to age-related conditions. However, further research is needed to better understand the skeletal muscle anabolic signaling response of the mTORC1 (mammalian target of rapamycin complex 1) pathway with repeated bouts of NMES. PURPOSE: To determine changes in skeletal muscle anabolic signaling in response to a 4-week NMES intervention in older adults. METHODS: Participants (n = 7) in this clinical trial were healthy, older adults (70.4 ± 2.9 years). NMES was applied to the quadriceps muscles for 40 min/treatment, 3x/week for 4 weeks (12 sessions). On Day 1 and Day 12 of the NMES intervention, skeletal muscle biopsies were obtained from the vastus lateralis Pre-NMES and 30 minutes Post-NMES and were analyzed for phosphorylation of mammalian target of rapamycin (mTOR) and p70-S6 Kinase 1 (S6K1) anabolic signaling proteins using the SDS-PAGE Western blot technique. Phosphorylation is expressed as the ratio of phosphorylated to total protein content. Data were analyzed using paired t-tests and data are reported as mean ± SE with statistical significance set at p ≤ 0.05. RESULTS: On Day 1, phosphorylation of S6K1 increased (Pre-NMES: 0.652 ± 0.145 AU vs. Post-NMES: 0.979 ± 0.151 AU, p = 0.037) and phosphorylation of mTOR increased (Pre-NMES: 0.464 ± 0.077 AU vs. Post-NMES: 1.046 ± 0.128 AU, p = 0.006) from Pre-NMES to Post-NMES. On Day 12, phosphorylation of S6K1 increased (Pre-NMES: 0.628 ± 0.108 AU vs. Post-NMES: 1.253 ± 0.288 AU, p = 0.048) with an increasing trend for mTOR (Pre-NMES: 0.485 ± 0.044 AU vs. Post-NMES: 0.700 ± 0.154 AU, p = 0.053) from Pre-NMES to Post-NMES. Phosphorylated S6K1 and mTOR protein content were not different between Day 1 and Day 12 at Pre-NMES (p \u3e 0.05) or at Post-NMES (p \u3e 0.05). CONCLUSION: The findings of this study suggest that the anabolic signaling response to a bout of NMES remains upregulated after 4-weeks of treatment; thus, the response is not attenuated with short-term repeated bouts of NMES. Funding: Research Enhancement Program Grant to J Mettler and L Kipp; Research Accelerator Grant, Texas State University, to J Mettler

Muscle force potentiation and motor unit firing patterns during fatigue : effects of muscular endurance training

textMuscular fatigue limits athletic performance as well as activities of daily living that require repetitive or sustained contractile activity. The decrease in force output or inability to maintain a given force level during fatigue occurs as the result of neural and muscle physiological factors. In contrast to muscle fatigue, potentiation is an increase in muscle force following voluntary muscle activity. The simultaneously occurring processes of potentiation and fatigue influence force output. The aims of this research were to investigate parameters used to potentiate muscle via electrical stimulation and voluntary contraction, and to better understand how muscle force is sustained, we studied single motor unit firing patterns and force potentiation following muscular endurance training. In study 1, electrical stimulation trains matched for pulse number of various frequencies and of increasing pulse number at a given frequency were administered to determine the effects of these stimulation parameters and of the force-time integral (FTI) produced during the train on potentiation magnitude. No difference in potentiation magnitude was found across trains of matched pulse number for frequencies of 15, 25, 30 and 50 Hz. Potentiation increased as pulse number increased and there was a positive correlation between potentiation and the FTI. In study 2, we measured maximal potentiation following conditioning contractions (CC) of 25%, 50% and 100% maximal voluntary contraction (MVC) and during a 25% MVC fatigue task, pre-post 8 weeks of muscular endurance training. Results showed significant potentiation for all CC intensities. Potentiation increased as CC intensity increased and CC duration required to achieve maximal potentiation decreased as CC intensity increased. Muscular endurance training resulted in increased maximal potentiation, and potentiation was greater during the fatigue task after training. Potentiation was also correlated to endurance time. In study 3, the effects of muscular endurance training on motor unit firing rates were investigated. There was a small increase in mean motor unit firing rates during the course of the fatigue task after training. This research contributes to our understanding of muscular force production and muscular endurance. The findings suggest that motor unit firing frequency and force potentiation may contribute to enhanced muscular endurance.Kinesiology and Health Educatio