Effects of arm-cycling exercise during triceps surae neuromuscular electrical stimulation on torque output and fatigue.

Abstract

This study compared the responses of arm-cycling during triceps surae neuromuscular electrical stimulation (NMES) on torque-time integral (TTI) and neuromuscular fatigue in healthy young adults. Achilles tendon vibration (VIB) (110 Hz) coupled with wide-pulse (WP) (1 ms) NMES (WP + VIB) of triceps surae alone or in combination with arm-cycling exercise (ARM-CYC) was delivered in two separate sessions in a randomised order (n = 22; 20 men; 29.9 ± 4.4 years). NMES intensity was set to elicit 20% of maximal voluntary isometric contraction (MVC) force. The stimulus pattern was comprised of four sets of 20 repetitions (5 s On and 5 s Off) superimposed to ongoing VIB with a 1-min inter-set interval. Time-torque integral (TTI) was measured for each NMES condition. MVC, voluntary activation level (VAL), peak twitch torque (Peak_twitch), and peak soleus (EMG_SOL), medial (EMG_MG), and lateral gastrocnemius (EMG_LG) electromyography were measured before and immediately after each condition. No significant differences were observed for TTI (P = 0.371) between ARM-CYC and WP + VIB protocols. MVC force and Peak_twitch torque decreased (P < 0.001) immediately after both conditions. No changes were observed for VAL (P = 0.418) and EMG_SOL, EMG_LG, and EMG_MG amplitudes (P = 0.061, 0.484, and 0.135), respectively. Rhythmic arm-cycling in combination with triceps surae NMES did not increase TTI compared to WP + VIB. This was accompanied with similar levels of peripheral fatigue with no indicative of central fatigue across both protocols. The lack of an ARM-CYC effect on torque output likely reflects the low intensity adopted, WP + VIB-induced ceiling effects, and/or enhanced inhibitory input to the triceps surae during combined tasks.