Effects Of A 4-week Neuromuscular Electrical Stimulation Treatment On Skeletal Muscle Endurance In Older Adults

Abstract

Neuromuscular electrical stimulation (NMES) is often used as a rehabilitative modality and evidence has suggested that high frequency NMES (HF-NMES) may elicit increases in muscle strength. However, little is known regarding the effects of HF-NMES treatment on voluntary skeletal muscle endurance. PURPOSE: The aim of this study was to determine the effect of a 4-week HF-NMES intervention on muscular endurance 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 yrs; NMES: n = 12; SHAM: n = 5) completed the study. The NMES group underwent NMES treatment to the quadriceps of each leg 3x/week for 4 weeks at a 60 Hz stimulation frequency. Electrodes were applied to the SHAM group, but no current was delivered. All subjects performed maximal voluntary contractions (MVC) and a knee extension isometric submaximal voluntary fatigue task at 50% MVC until fatigue criteria were met. Surface electromyography (sEMG) of the vastus lateralis (VL) and vastus medialis (VM) muscles were recorded during the fatigue task and quantified for root mean square (RMS) EMG (percent rate of change during the fatigue task) and median frequency (MF) to examine changes in muscle activation. 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 < 0.05. RESULTS: MVC increased 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 changes in SHAM (p = 0.96). No differences were observed pre-post training, respectively for muscular endurance time (NMES: 159.3 ± 20.1 s vs 141.9 ± 21.2 s, p = 0.29; SHAM: 242.2 ± 43.3 s vs 202.9 ± 23.3 s, p = 0.13), RMS EMG rate of change (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) and MF EMG (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). CONCLUSION: Treatment with HF-NMES did not improve muscle endurance or EMG-related parameters. HF-NMES may not be efficacious when the goal is to improve skeletal muscle endurance.