Indexed on: 20 Dec '18Published on: 20 Dec '18Published in: Applied physiology, nutrition, and metabolism = Physiologie appliquee, nutrition et metabolisme
Increases in muscle size and strength similar to those with high resistance load can be achieved by combining lower-loads with continuous blood flow restriction (BFR). However, high ratings for distress have been reported for continuous BFR. Therefore, we investigated the efficacy (metabolic stress) of BFR applied only during intervals in resistance exercise. Seven healthy men performed three 1-min sets of plantar flexion (30 reps/min), with 1-min rest intervals under 4 conditions: low-load resistance exercise (L, 20 % 1-RM) without BFR (L-noBFR), L with BFR during exercise sets (L-exBFR), L with BFR during resting interval periods (L-intBFR), and L with continuous BFR during both exercises and intervals (L-conBFR). Based on the results of the first experiment, we performed additional protocols using moderate-load (M, 40% 1-RM) with intermittent (exercises and intervals) BFR (M-exBFR and M-intBFR). Intramuscular metabolic stress, defined as phosphocreatine and intramuscular pH decrease, was evaluated by 31P-magnetic resonance spectroscopy. Perceived exertion (RPE) was also assessed. At the end of exercise, total phosphocreatine and intramuscular pH decrease were similar in L-noBFR, L-intBFR and L-exBFR, and significantly less than those in L-conBFR (p<0.05). By contrast, those changes in M-intBFR but in M-exBFR were similar to those in L-conBFR. Nevertheless, RPE was lower in M-intBFR than in both M-exBFR and L-conBFR (p<0.05). The effect of intermittent BFR during exercise might be insufficient for metabolic stress when using a low-load. However, effective metabolic stress for muscular adaptation could be obtained by moderate-load resistance exercise with BFR during intervals with less ischemic duration and discomfort.