Blood Flow Restriction Only Increases Myofibrillar Protein Synthesis with Exercise

Purpose Combining blood flow restriction (BFR) with exercise can stimulate skeletal muscle hypertrophy. Recent observations in an animal model suggest that BFR performed without exercise can also induce anabolic effects. We assessed the impact of BFR performed both with and without low-load resistance-type exercise (LLRE) on in vivo myofibrillar protein synthesis rates in young men. Methods Twenty healthy young men (age: 24±1 y, BMI: 22.9±0.6 kg/m2) were randomly assigned to remain in resting condition (REST+/-BFR; n=10), or to perform LLRE (LLRE+/-BFR at 20%1RM; n=10), combined with two 5-min cycles of single leg BFR. Myofibrillar protein synthesis rates were assessed during a 5-h post-BFR period by combining a primed continuous L-[ring-13C6]phenylalanine infusion with the collection of blood samples, and muscle biopsies from the BFR leg and the contralateral control leg. Phosphorylation status of anabolic signaling (mTOR pathway) and metabolic stress (ACC) related proteins, as well as mRNA expression of genes associated with skeletal muscle mass regulation were assessed in the collected muscle samples. Results Under resting conditions, no differences in anabolic signaling or myofibrillar protein synthesis rates were observed between REST+BFR and REST (0.044±0.004 vs 0.043±0.004 %/h, respectively; P=0.683). In contrast, LLRE+BFR increased myofibrillar protein synthesis rates by 10±5% compared with LLRE (0.048±0.005 vs 0.043±0.004 %/h, respectively; P=0.042). Furthermore, compared with LLRE, LLRE+BFR showed higher phosphorylation status of ACC and 4E-BP1 as well as elevated mRNA expression of MuRF1 (all P

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