Masashi Omokawa

Intramuscular metabolism during low-intensity resistance exercise with blood flow restriction

Although recent studies have reported that low-intensity resistance training with blood flow restriction could stress the muscle effectively and provide rapid muscle hypertrophy and strength gain equivalent to those of high-intensity resistance training, the exact mechanism and its generality have not yet been clarified. We investigated the intramuscular metabolism during low-intensity resistance exercise with blood flow restriction and compared it with that of high-intensity and low-intensity resistance exercises without blood flow restriction using (31)P-magnetic resonance spectroscopy. Twenty-six healthy subjects (22 +/- 4 yr) participated and performed unilateral plantar flexion (30 repetitions/min) for 2 min. Protocols were as follows: low-intensity exercise (L) using a load of 20% of one-repetition maximum (1 RM), L with blood flow restriction (LR), and high-intensity exercise using 65% 1 RM (H). Intramuscular phosphocreatine (PCr) and diprotonated phosphate (H(2)PO(4)(-)) levels and intramuscular pH at rest and during exercise were obtained. We found that the PCr depletion, the H(2)PO(4)(-) increase, and the intramuscular pH decrease during LR were significantly greater than those in L (P < 0.001); however, those in LR were significantly lower than those in H (P < 0.001). The recruitment of fast-twitch fiber evaluated by inorganic phosphate splitting occurred in only 31% of the subjects in LR, compared with 70% in H. In conclusion, the metabolic stress in skeletal muscle during low-intensity resistance exercise was significantly increased by applying blood flow restriction, but did not generally reach that during high-intensity resistance exercise. This new method of resistance training needs to be examined for optimization of the protocol to reach equivalence with high-intensity resistance training.

Dose effect on intramuscular metabolic stress during low-intensity resistance exercise with blood flow restriction

Our previous study reported that metabolic stress in skeletal muscle achieved by combining moderate blood flow restriction (BFR) with low-intensity resistance exercise at 20% of one repetition maximum (1 RM) could not reach the level achieved by high-intensity resistance exercise. Since the previous protocol is typical of current regimens of this type, we sought in this study to optimize the exercise protocol for low-intensity resistance exercise with BFR by examining the dose effects of exercise intensity and pressure. Twelve healthy subjects participated in this study. They were asked to perform unilateral plantar flexion for 2 min (30 repetitions/min) under six different conditions: two resistance exercises (20% 1 RM and 65% 1 RM) without BFR, and four BFR protocols. The four BFR protocols included three different exercise intensities (20, 30, and 40% 1 RM) with moderate pressure (MP) using 130% of systolic blood pressure (147+/-17 mmHg, mean+/-SD) and 20% 1 RM with high pressure at 200 mmHg. Intramuscular metabolites and pH were obtained by 31P-magnetic resonance spectroscopy. Significant dose effects on intramuscular metabolites and pH were observed for exercise intensity (P<0.001) but not for BFR pressure. The BFR protocol combining 30% 1 RM with MP had similar results as the high-intensity load at 65% 1 RM. Intramuscular metabolic stress during BFR exercise might be susceptible to increasing exercise intensity. To replace high-intensity resistance exercise, the BFR protocol might require an intensity of >or=30% 1 RM.

Low-intensity exercise can increase muscle mass and strength proportionally to enhanced metabolic stress under ischemic conditions

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.

Blood Flow Restriction Exercise in Sprinters and Endurance Runners

PURPOSE We demonstrated that blood flow restriction (BFR) remarkably enhances muscular metabolic stress in resistance exercise, although there is a wide range of individual differences in the responses. It is possible that these differences could be due to training status and muscular physiological characteristics. We investigated intramuscular metabolic responses during low-intensity resistance exercise with BFR between two different types of track athletes. METHODS Twelve age-matched male track athletes (sprinter group, n = 6; endurance runner group, n = 6) were recruited and performed unilateral plantarflexion (30 repetitions per minute). The exercise protocols were as follows: low-intensity exercise at 20% of one-repetition maximum (1RM) (L), high-intensity exercise at 65% 1RM without BFR (1.3 times of systolic blood pressure), L with BFR for 2 min (L-BFR), and prolonged exercise time in L-BFR for 3 min (prolonged BFR). Metabolic stress, defined as phosphocreatine and intramuscular pH decrease, and muscle fiber recruitment were evaluated using P magnetic resonance spectroscopy. RESULTS Endurance runners showed higher peak oxygen uptake and lower muscle strength than sprinters. Phosphocreatine decreases in endurance runners during exercise with BFR protocols were significantly greater than those in sprinters (P < 0.05), although those occurring during L were significantly lower than those in sprinters (P < 0.05). The changes in intramuscular pH and the incidence of fast-twitch fiber recruitment did not show a statistical difference between the two groups. Phosphocreatine decreases in L-BFR were significantly correlated with peak oxygen uptake (P < 0.05). CONCLUSIONS The effects of low-intensity resistance exercise with BFR are greater in endurance runners according to higher aerobic capacity.

Intramyocellular lipid is increased in the skeletal muscle of patients with dilated cardiomyopathy with lowered exercise capacity

Title Intramyocellular lipid is increased in the skeletal muscle of patients with dilated cardiomyopathy with lowered exercise capacity Author(s) Hirabayashi, Kagami; Kinugawa, Shintaro; Yokota, Takashi; Takada, Shingo; Fukushima, Arata; Suga, Tadashi; Takahashi, Masashige; Ono, Taisuke; Morita, Noriteru; Omokawa, Masashi; Harada, Kuniaki; Manabe, Noriko; Shirato, Hiroki; Matsushima, Shouji; Okita, Koichi; Tsutsui, Hiroyuki Citation International Journal of Cardiology, 176(3), 1110-1112 https://doi.org/10.1016/j.ijcard.2014.07.113 Issue Date 2014-10-20

Pioglitazone improves whole-body aerobic capacity and skeletal muscle energy metabolism in patients with metabolic syndrome

Low aerobic capacity is a strong and independent predictor of all‐cause mortality in patients with metabolic syndrome (MetS). Here, we investigated the effects of pioglitazone treatment on whole‐body aerobic capacity and skeletal muscle energy metabolism in MetS patients.

Effects of oral single-dose administration of sarpogrelate hydrochloride on saturation O(2) of calf muscle during plantar flexion exercise.

To investigate the effects of a 100-mg oral single-dose administration of sarpogrelate hydrochloride (SH) on saturation O(2) (StO(2)) of calf muscle in healthy subjects experiencing simulated peripheral arterial disease (0.6 ankle brachial pressure index). Ten subjects performed three kinds of plantar flexion exercises at a work rate of 50% of maximal volunteer contraction for 4 min by using cuff occlusion ischemia,. Subjects performed a control test (C) without ischemia and SH, an ischemia test (I) without SH, and an I + SH test with ischemia. StO(2), blood pressures (BP), and heart rate (HR) were measured through all experiments. At the end of the exercise, the decrease in StO(2) from baseline in the C and I + SH tests was significantly less than that in the I test (p < 0.05, respectively). However, there were no significant differences in mean BP or HR in any of the exercise conditions. These results indicated that an oral single-dose administration of SH might improve peripheral circulation independent of any changes in BP and HR.