Muscle Fatigue After Isometric Exercise With And Without Neuromuscular Electrical Stimulation

Neuromuscular electrical stimulation (NMES) has drawn attention and has been used in sportsand rehabilitation recently. The muscle activation pattern during the NMES is different from thatduring the voluntary contractions, where high-threshold motor units can only be recruited at highforce levels. PURPOSE: This study aims to examine the acute effects of combining voluntary isometricexercise with and without NMES on neuromuscular fatiguing parameters in elbow flexormuscles. METHODS: Thirteen adults (twelve men: age = 23 ± 6 years, height = 178.6 ± 7.4 cm, bodymass = 85.5 ± 15.4 kg; ten women: age = 23 ± 3 years, height = 162.2 ± 8.1 cm, body mass = 59.1 ± 5.8 kg) completed this 3-visit study. In each visit, every participant went through a pre-randomly-determined exercise intervention with their dominant elbow flexor muscles [voluntaryisometric exercise (ISO): 10 sets of 10-s voluntary contraction at 50% of the pre-determinedmaximal isometric strength; or combining NMES (applied on the biceps muscle belly; pulsewidth: 1 ms; frequency: 100 Hz) with ISO (NMES+ISO): 10 sets of 10-s concurrent ISO with theNMES at 50% of the maximal isometric strength], except the first visit served as the control (restfor 5 minutes). A 10-s rest interval was provided between consecutive sets. Before andimmediately after the intervention, isometric strength, voluntary activation, and resting twitchwere measured on the same muscle group. Separate two-way (condition × time) repeatedmeasures analysis of variance (ANOVA) tests were used to examine the potential changes of thedependent variables following interventions among different conditions. RESULTS: There is no significant condition by time interaction for the isometric strength (p = 0.461), but there were main effects for time (p < 0.001) and condition (p = 0.02), indicating thatthe isometric strength was significantly decreased following interventions. For the voluntaryactivation and resting twitch, the ANOVA tests did not find any significant interactions or maineffects. CONCLUSION: Our data does not suggest that superimposing NMES on voluntary isometricexercise at medium exercise intensity induces differential fatiguing effect than voluntaryisometric exercise alone. Supported by: Nasa CT Space Grant was used to fund this reserach and purchase necessary equipment.