Recent studies have reported that low-intensity resistance training with blood flow restriction (BFR) could provide the rapid muscle hypertrophy and strength gain equivalent to those of high-intensity resistance training. Its mechanism has been speculated to be caused by the increased metabolic stress in exercising muscle; however it remains unclear. We measured the intramuscular metabolism during resistance exercise using ³¹P-magnetic resonance spectroscopy (MRS). In the present study, we sought to optimize the exercise protocol for BFR exercise by examining a variety of the intensity of exercise and the pressure of BFR. The exercise was performed unilateral plantar flexion (30 repetitions/min) for 2 min. Intramuscular phosphocreatine (PCr) and pH were obtained by ³¹P-MRS. The change of intramuscular PCr and pH during low-intensity resistance exercise (20% 1RM) with moderate BFR (130% of systolic blood pressure) was significantly greater than that during exercise of similar intensity without BFR. However, those changes were lower than that during high-intensity exercise (65% 1RM) without BFR. The changes of PCr and pH during BFR protocol with 30% 1RM had similar levels of changes in the high-intensity exercise. In contrast, the increased pressure of BFR had only a little effect. Our results suggested that the intramuscular metabolic stress during BFR exercise might be associated with exercise intensity. To replace high-intensity resistance exercise, the BFR protocol with the intensity of at least 30% 1RM might be required.

DESCENTE SPORTS SCIENCE Vol.31/THE DESCENTE AND ISHIMOTO MEMORIAL FOUNDATION FOR THE PROMOTION SPORTS SCIENCE