Kinetics of Intramuscular Inorganic Phosphate During Low Intensity Exercise With Blood Flow Restriction

Abstract

Under the same loading condition, dynamic exercise combined with blood flow restriction (BFR) causes more rapid reduction in muscle power (muscle fatigue) than without blood flow restriction. Furthermore, low-intensity resistance exercise combined with BFR causes as much muscle fatigue as that of high-intensity exercise. However, the mechanisms of such exercise induced muscle fatigue with BFR are unknown. Recent studies have suggested that the accumulation of inorganic phosphate (Pi), which accelerates under ischemic exercise, may also contribute to muscle fatigue. PURPOSE: To investigate the kinetics of intramuscular Pi concentration during resistance exercise with blood flow restriction. METHODS: Ten healthy young men (24.9Ã'±5.4 yrs, 174.4Ã'±7.1 cm, 71.1Ã'±10.0 kg) performed unilateral planter flexion exercise (30 reps Ã_ 1 set followed by 15 reps Ã_ 3 sets with 30-seconds rest between sets) in a supine position in phosphorus magnetic resonance spectroscopy (MRS system). Each subject underwent three exercise conditions; at low-intensity (20%1-RM) either with (L-BFR) or without (L-CON) blood flow restriction, and high-intensity exercise (HIGH; 70%1RM, 15 reps Ã_ 3 sets with 3 min rest between sets) without blood flow restriction. For L-BFR, proximal part of thigh in the exercising leg was pressurized at 220 mmHg with inflexible cuff (5cm wide). Change in intramuscular Pi was monitored continuously during the entire protocol. RESULTS: During exercise, Pi increased progressively and similarly for L-BFR and L-CON group. However, during the rest interval, the rate of decline (recovery rate) was slower in L-BFR such that the % change in Pi was significantly higher in L-BFR than L-CON before the initiation of following set. As a result, the % change in Pi at the end of 4th set was significantly higher in L-BFR than L-CON (L-BFR; 94.0Ã'±30.3 %, L-CON; 64.0Ã'±20.2 %). However, % change in Pi for HIGH was still significantly higher than L-BFR and L-CON. CONCLUSIONS: Low-intensity resistance exercise combined with blood flow restriction induced accumulation of Pi faster than control exercise mainly due to the delayed recovery during the rest periods.