PURPOSE: This study compared endurance and neuromuscular function after bouts of low-load (LL), high-load (HL), and LL blood flow-restricted (LL(BFR)) resistance exercise. METHODS: Eight recreationally active male subjects completed three sets of dynamic knee extensions to volitional failure under three conditions: HL (70% peak torque), LL (20% peak torque), and LL(BFR) (20% peak torque with an occlusive cuff inflated to 180 mm Hg wrapped around the thigh). Before and immediately after exercise, isometric torque, central activation, electrically evoked torque, and muscle activation via surface EMG were measured. RESULTS: Isometric torque and evoked torque decreased an average of 37% and 40%, respectively (P < 0.01) in all conditions after exercise. There were no differences in the toque decrements between the conditions (P > 0.05). Percent central activation did not change after any condition (P = 0.09). Rate of torque development declined an average of 26% after all three conditions (P = 0.003), and rate of half-relaxation time was depressed by 48% after the HL condition (P = 0.004) only. EMG amplitude was greater in the HL condition at the beginning and end of exercise compared with the LL and LL(BFR) conditions (P = 0.001). At the end of exercise, EMG amplitude rose 19% (P = 0.02) and was not different among conditions (P > 0.05). Subjects performed more repetitions during the LL and LL(BFR) conditions (P < 0.05). CONCLUSION: Although LL and LL(BFR) resistance exercise to volitional failure exhibit lower levels of muscle activation than HL exercise, similar torque decrements occur after all bouts of resistance exercise, and the muscle fatigue can be attributed to peripheral factors.
