Contractile function and sarcolemmal permeability after acute low-load resistance exercise with blood flow restriction.

Conflicting findings have been reported regarding muscle damage with low-intensity resistance exercise with blood flow restriction (BFR) by pressure cuffs. This study investigated muscle function and muscle fibre morphology after a single bout of low-intensity resistance exercise with and without BFR. Twelve physically active subjects performed unilateral knee extensions at 30% of their one repetition maximum (1RM), with partial BFR on one leg and the other leg without occlusion. With the BFR leg, five sets were performed to concentric torque failure, and the free-flow leg repeated the exact same number of repetitions and sets. Biopsies were obtained from vastus lateralis before and 1, 24 and 48 h after exercise. Maximum isometric torque (MVC) and resting tension were measured before and after exercise and at 4, 24, 48, 72, 96 and 168 h post-exercise. The results demonstrated significant decrements in MVC (lasting ≥48 h) and delayed onset muscle soreness in both legs, and increased resting tension for the occluded leg both acutely and at 24 h post-exercise. The percentage of muscle fibres showing elevated intracellular staining of the plasma protein tetranectin, a marker for sarcolemmal permeability, was significantly increased from 9% before exercise to 27-38% at 1, 24 and 48 h post-exercise for the BFR leg. The changes in the free-flow leg were significant only at 24 h (19%). We conclude that an acute bout of low-load resistance exercise with BFR resulted in changes suggesting muscle damage, which may have implications both for safety aspects and for the training stimulus with BFR exercise.