The present study was designed to provide mechanistic insight into the time course and etiology of muscle fatigue development and recovery during and after low-intensity exercise when it is combined with blood flow restriction (BFR).Methods
Seventeen resistance-trained males completed four sets of low-intensity isotonic resistance exercise under two experimental conditions: knee extension exercise (i) with BFR and (ii) without BFR (CON). Neuromuscular tests were performed before, during (immediately after each set of knee extension exercise), and 1, 2, 4, and 8 min after each experimental condition. Maximal voluntary torque, quadriceps twitch torque in response to paired electrical stimuli at 10 Hz (PS10) and 100 Hz (PS100), PS10·PS100−1 ratio as an index of low-frequency fatigue, and voluntary activation were measured under isometric conditions. Perceptual and EMG data were recorded during each exercise condition.Results
After the first set of exercise, BFR induced significantly greater reductions in maximal voluntary torque, PS100, and PS10·PS100−1 ratio compared with CON. These parameters progressively declined throughout the BFR protocol but recovered substantially within 2 min postexercise when blood flow was restored. Neither a progressive decline in the course of the exercise protocol nor a substantial recovery of these parameters occurred during and after CON. Only at exercise termination, voluntary activation differed significantly between BFR and CON with greater reductions during BFR.Conclusion
At the early stage of exercise, BFR exacerbated the development of muscle fatigue mainly due to a pronounced impairment in contractile function. Despite the high level of muscle fatigue during BFR exercise, the effect of BFR on muscle fatigue was diminished after 2 min of reperfusion, suggesting that BFR has a strong but short-lasting effect on neuromuscular function.