title: Low-intensity exercise can increase muscle mass and strength proportionally to enhanced metabolic stress under ischemic conditions.
abstract: Skeletal muscle bulk and strength are becoming important therapeutic targets in medicine. To increase muscle mass, however, intensive, long-term mechanical stress must be applied to the muscles, and such stress is often accompanied by orthopedic and cardiovascular problems. We examined the effects of circulatory occlusion in resistance training combined with a very low-intensity mechanical load on enhancing muscular metabolic stress and thereby increasing muscle bulk. Muscular metabolic stress, as indicated by the increases in inorganic phosphate (P(i)) and a decrease in intramuscular pH, was evaluated by (31)P-magnetic resonance spectroscopy during unilateral plantar-flexion at 20% of the one-repetition maximum (1-RM) with circulatory occlusion for 2 min in 14 healthy, male untrained participants (22 yr) at baseline. Participants performed two sets of the same exercise with a 30-s rest between sets, 2 times/day, 3 days/wk, for 4 wk. The muscle cross-sectional area (MCA) of the plantar-flexors and the 1-RM were measured at baseline and after 2 and 4 wk of training. MCA and 1-RM were significantly increased after 2 and 4 wk (P < 0.05, respectively). The increase in MCA at 2 wk was significantly (P < 0.05) correlated with the changes in P(i) (r = 0.876) and intramuscular pH (r = 0.601). Furthermore, the increases in MCA at 4 wk and 1-RM at 2 wk were also correlated with the metabolic stress. Thus enhanced metabolic stress in exercising muscle is a key mechanism for favorable effects by resistance training. Low-intensity resistance exercise provides successful outcomes when performed with circulatory occlusion, even with a short training period.
authors.affiliation: Department of Cardiovascular Medicine, Hokkaido University Graduate School of Medicine, 23 Bunkyo-dai, Ebetsu, Hokkaido, Japan.
authors.forename: Shingo
authors.initials: S
authors.lastname: Takada
authors.forename: Koichi
authors.initials: K
authors.lastname: Okita
authors.forename: Tadashi
authors.initials: T
authors.lastname: Suga
authors.forename: Masashi
authors.initials: M
authors.lastname: Omokawa
authors.forename: Tomoyasu
authors.initials: T
authors.lastname: Kadoguchi
authors.forename: Takashi
authors.initials: T
authors.lastname: Sato
authors.forename: Masashige
authors.initials: M
authors.lastname: Takahashi
authors.forename: Takashi
authors.initials: T
authors.lastname: Yokota
authors.forename: Kagami
authors.initials: K
authors.lastname: Hirabayashi
authors.forename: Noriteru
authors.initials: N
authors.lastname: Morita
authors.forename: Masahiro
authors.initials: M
authors.lastname: Horiuchi
authors.forename: Shintaro
authors.initials: S
authors.lastname: Kinugawa
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Tsutsui
mesh_terms: D000328:Adult; D015444:Exercise; D006801:Humans; D007511:Ischemia / Q000503:physiopathology*; D019194:Ischemic Preconditioning / Q000379:methods; D008297:Male; D009119:Muscle Contraction; D053580:Muscle Strength; D018482:Muscle, Skeletal / Q000503:physiopathology*; D009929:Organ Size; D055070:Resistance Training / Q000379:methods*; D013312:Stress, Physiological