Article

Blood flow restriction during low-intensity resistance exercise increases S6K1 phosphorylation and muscle protein synthesis

Texas A&M University - Galveston, Galveston, Texas, United States
Journal of Applied Physiology (Impact Factor: 3.43). 10/2007; 103(3):903-10. DOI: 10.1152/japplphysiol.00195.2007
Source: PubMed

ABSTRACT Low-intensity resistance exercise training combined with blood flow restriction (REFR) increases muscle size and strength as much as conventional resistance exercise with high loads. However, the cellular mechanism(s) underlying the hypertrophy and strength gains induced by REFR are unknown. We have recently shown that both the mammalian target of rapamycin (mTOR) signaling pathway and muscle protein synthesis (MPS) were stimulated after an acute bout of high-intensity resistance exercise in humans. Therefore, we hypothesized that an acute bout of REFR would enhance mTOR signaling and stimulate MPS. We measured MPS and phosphorylation status of mTOR-associated signaling proteins in six young male subjects. Subjects were studied once during blood flow restriction (REFR, bilateral leg extension exercise at 20% of 1 repetition maximum while a pressure cuff was placed on the proximal end of both thighs and inflated at 200 mmHg) and a second time using the same exercise protocol but without the pressure cuff [control (Ctrl)]. MPS in the vastus lateralis muscle was measured by using stable isotope techniques, and the phosphorylation status of signaling proteins was determined by immunoblotting. Blood lactate, cortisol, and growth hormone were higher following REFR compared with Ctrl (P < 0.05). Ribosomal S6 kinase 1 (S6K1) phosphorylation, a downstream target of mTOR, increased concurrently with a decreased eukaryotic translation elongation factor 2 (eEF2) phosphorylation and a 46% increase in MPS following REFR (P < 0.05). MPS and S6K1 phosphorylation were unchanged in the Ctrl group postexercise. We conclude that the activation of the mTOR signaling pathway appears to be an important cellular mechanism that may help explain the enhanced muscle protein synthesis during REFR.

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    ABSTRACT: Short-term slow walk training combined with leg blood flow reduction (BFR-W) produces thigh muscle hypertrophy and strength gains in young and elderly adults. However, the impact of long-term BFR-W training on muscle size and function has not been explored. PURPOSE: To determine the physiological responses to relatively long-term BFR-W training with different exercise frequencies on muscle mass and strength, as well as functional ability, in older women and men. METHODS: Sixteen older adults (60-78 yrs) were randomized into either BFR-W (n=8: 6 women, 2 men) or non-exercise control (CON) (n=8: 6 women, 2 men) groups. BFR-W group walked on a treadmill for 20 min at 67 m/min. Initially BFR-W group exercised 5 days/wk for 6 weeks, followed by 2 days/wk for 12 weeks and then once a week for 24 weeks. The BFR-W group wore pressure cuff belts (5 cm wide) on both legs during training (external compression: 160-200 mmHg). Ultrasound estimated muscle mass, knee extension strength, and functional ability (Up & Go and chair stand tests) were assessed before (pre), at 6 th week (post-1), at 18 th week (post-2, BFR-walk only), and at 42 nd week (post-3, BFR-walk only). RESULTS: After the initial 6 weeks of training, thigh muscle mass increased by 12% (pre: 5.4±0.6 kg; post-1: 6.0±0.6 kg, P0.10). Isometric and isokinetic (30, 90 and 180 deg/sec) knee extension torques increased in BFR-walk (6 to 15%, P0.10). Functional ability also increased significantly, but only in BFR-W group (P0.05). However, thigh muscle mass decreased (5.6±0.5 kg) following 24 weeks of reduced training frequency (once a week, post-3) compared with the 18 th week (post-2) period, although isometric strength was maintained. CONCLUSION: slow walk training combined with leg blood flow reduction increased muscle size and strength when performed 5 days/wk in the elderly (post-1). Furthermore, a 2 days/wk training regimen can maintain the training response and increase bone turnover over a 12 week period (post-2). However, training-induced increases in thigh muscle size decreased during once a week training (post-3).
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