Effects Of Current Amplitude And Pulse Duration Modulation On Neuromuscular Fatigue During Repetitive Electrical Stimulation

Abstract

Neuromuscular electrical stimulation (NMES) is effective for preventing muscle atrophy. However, rapid muscle fatigue and discomfort during the stimulation are major obstacles for prolonged force production at moderate levels of force production which limit its use for functional purposes. Previous studies have shown that long stimulus pulse widths can reduce muscle fatigue. However only very low force levels (5-10% maximum voluntary isometric contraction (MVIC)) have been investigated. PURPOSE: To compare the effects of two different combinations of NMES parameters on the degree of muscle fatigue and pain during evoked repetitive isomeric contractions of 25% MVIC. METHODS: Stimulating electrodes were placed over the right quadriceps of 8 males and 2 females (24 ± 1). The participant’s MVIC was measured in a practice session performed at least 48 hours prior to the first test date. Two testing sessions were performed at least 48 hours apart and in random order. In the one session, a stimulus with a long pulse duration (1000 μs) and a low current amplitude set (LL) to evoke a contraction force of 25% MVIC at 30 Hz was applied repetitively for 2 minutes. The participants rated their pain during the stimulation a scale of 0 to 10. The other test session followed the same protocol with the exception that a shorter pulse duration (200 μs) and a high current amplitude set (SH) was used to produce 25% MVIC force at 30 Hz. Fatigue and pain comparisons were made using one-way ANOVAs with repeated measures. RESULTS: Percent muscle fatigue was significantly lower for LL than for SH (29.20 ± 2.12 vs. 33.89 ± 2.01 %, p = 0.002). The force recovery rate was significantly higher for LL than for SH (0.75 ± 0.06 vs. 0.53 ± 0.07 N/5s, p = 0.019). Pain scores were also lower for LL than for SH (4.38 ± 0.83 vs. 5.75 ± 0.49, p = 0.033). CONCLUSION: The use of longer pulse durations helps to reduce muscle fatigue and pain during NMES for moderate-level contractions of 25% MVIC.