Acute Effects of Fatiguing Low-Load Leg Extension Muscle Actions on Maximal Strength and Neuromuscular Function

Purpose The purpose of this investigation was to examine the acute effects of low-load unilateral submaximal leg extension muscle actions with and without blood flow restriction (BFR) on maximal voluntary isometric contraction (MVIC) torque, electromyographic (EMG) amplitude (AMP) and EMG mean power frequency (MPF). Methods Twelve (mean +/- SD; 23 +/- 4 years) men performed 75 submaximal (1 x 30, 3 x 15) unilateral leg extension muscle actions with or without BFR. Before and immediately after the 75 reps, ultrasound measures and MVIC muscle actions were performed, and surface EMG was simultaneously assessed from the vastus lateralis. BFR was applied at 60% of total arterial occlusion. Separate repeated measures ANOVA's, and Bonferroni corrected t-tests were performed to examine MVIC, EMG AMP, and EMG MPF. An alpha of P < 0.05 was considered statistically significant for all comparisons. Results There was no significant (P = 0.077) interaction or main effect for Condition (P = 0.442) for EMG AMP. There was, however, an interaction (P = 0.014) for EMG MPF (posttest BFR decrease > posttest non-BFR decrease). There was a main effect for Time, collapsed across Condition, for MVIC torque (P < 0.001; (mean +/- SD; 294.9 +/- 20.1 N center dot m to 138.6 +/- 12.2 N center dot m), but no main effect for Time for EMG AMP. Conclusion The findings of the present study indicated there were similar fatigue-induced decreases in MVIC torque and mode-specific decreases in EMG mean power frequency between the BFR and non-BFR conditions, but no changes in EMG amplitude. The decrease in MVIC torque may be due, in part, to the fatigue-induced buildup of metabolic byproducts that adversely affects excitation-contraction coupling and force output.