Oxygen is an essential molecule for all cellular activities including growth. Either excessive or deficient oxygen supply to cells induces the various responses of the cells. In the field of pathophysiology, effects of blood flow restriction on various organs have been studied for the past ∼130 years. Subsequently, the roles of oxygen at subcellular level have been studied in vitro. Although a number of studies show that a low-intensity exercise (20∼50% of one repetition maximum) with a moderate tourniquet restriction of blood flow results in increases in muscular strength and size, the mechanisms for this muscular adaptation remain unclear. In particular, it is uncertain whether the low-intensity exercise with blood flow restriction using a tourniquet causes the hypoxia or hyperoxia in the muscle, and then what signals leading to muscular hypertrophy are activated inside and/ or outside the cells. Also, it is not well understood what side effects occur in addition to conferring the benefits of strength gains. The review summarizes recent studies on the muscular adaptations to oxygen environment and discusses the mechanisms that may be involved in the resistance exercise with restricted blood flow.
Exercise is a potent stimulus to GH secretion. However it is unclear if exercise-induced GH release differs between different muscle groups, i.e., arm and leg exercise, when performed at equivalent exercise intensity. The purpose of this study was to compare the GH responses to an acute resistance exercise, combined with restriction of muscular venous blood flow (KAATSU), in muscle groups of the arm and leg. Five young male subjects performed two types of exercise tests, arm and leg exercise, on separate days. The intensity of exercise was 20% of 1-RM, which was measured at least 1 week before the experiment. The external restriction pressure during the KAATSU exercise was selected 50% higher than each measured-arm and estimated-leg systolic blood pressure. Venous blood samples were obtained prior to the start of exercise, immediately post exercise, and 15- and 60-min after exercise, and blood lactate (LA), growth hormone (GH), noradrenaline (NA), hematocrit, albumin and Na/K concentrations were measured. Significant elevations were apparent immediately post and 15-min after exercise for LA and at immediately post, 15- and 60-min after exercise for GH in both arm and leg exercise. Significant elevation was also observed after exercise for NA in both arm and leg, but leg exercise resulted in a greater increase in NA than arm at immediately post exercise. Change in plasma volume after exercise was not different between two exercises. These results suggest that GH secretory responses to exercise may be similar between the arm and leg when performed at equivalent exercise intensity and restriction stimulus.
We investigated the acute effects of “Kaatsu” resistance exercise and other types of exercise on muscle oxygenation and plasma growth hormone. Six young male bodybuilders performed leg extension exercise according to four exercise regimens: low-intensity [∼30% of one repetition maximum (1RM)] exercise with moderate occlusion (LO-Kaatsu), low-intensity (∼50% 1RM) exercise with slow movement and tonic force generation (3 s for lowering and 3 s for lifting actions, 1-s pause, and no relaxing phase; LST), low-intensity (same as LST) isometric exercise at 45° knee angle (ISO), and high-intensity (∼80% 1RM) exercise with normal movement speed (HN), commonly used for gaining muscular size and strength. The muscle oxygenation level measured with near-infrared continuous-wave spectroscopy (NIRcws) showed the largest changes during and after LO-Kaatsu among all regimens. The minimum oxygenation level during LO-Kaatsu was the lowest among the four exercise regimens. On the other hand, the increases in muscle oxygenation after LO-Kaatsu were the largest among the four regimens. Plasma GH and blood lactate concentrations after LO-Kaatsu, LST and HN were significantly (P < 0.05) higher than those after ISO, but there were no significant differences among those after LO-Kaatsu, LST and HN. The results indicate that “Kaatsu” resistance exercise causes marked changes in muscle oxygenation level and circulating growth hormone, both of which may be related to muscular hypertrophy.
KAATSU training is a novel method for strength training to induce muscle strength and hypertrophy. The purpose of the present study was to investigate the hemodynamic and autonomic nervous responses to the restriction of femoral blood flow by KAATSU. Ultrasonography, echocardiography and impedance cardiography were performed in ten healthy male volunteers aged 34 ± 1.5 before (pre), during and after (post) pressurization on both legs with KAATSU belts placed around proximal portion of both legs. The parameters measured were as follows; the superficial femoral arterial blood flow, left ventricular end-diastolic/systolic dimension (LVDd/LVDs), cardiac output (CO), stroke volume (SV), diameter of inferior vena cava (IVC), heart rate (HR), mean blood pressure (mBP), total peripheral resistance (TPR) and heart rate variability (HRV). The pressurization on both legs with KAATSU suppressed venous blood flow, and markedly induced pooling of blood into the legs with pressure-dependent reduction of femoral arterial blood flow. The application of 200 mmHg KAATSU decreased femoral arterial blood flow, LVDd, CO, SV and IVC significantly. HR tended to increase, and TPR increased significantly, but mBP did not change significantly. In addition, high frequency (HFRR), a marker of parasympathetic activity, decreased during KAATSU, while LFRR/HFRR, a quantitative marker of sympathetic autonomic nervous activity, increased significantly. These results indicate that the application of KAATSU on both legs induces venous pooling in the legs, and then inhibits venous return. The reduction of venous return causes a decrease of IVC diameter, cardiac size and stroke volume with an increase in TPR and LFRR/HFRR. Thus, the KAATSU training appears to become a useful method for potential countermeasure like lower body negative pressure (LBNP) against orthostatic intolerance for long-term bed rest or space flight as well as strength training to induce muscle strength and hypertrophy.
The purpose of this study was to examine the effect of low-intensity (20% of 1-RM) resistance training (LIT) combined with restriction of muscular venous blood flow (KAATSU) on muscle fiber size using a biopsy sample. Three young men performed LIT-KAATSU (restriction pressure 160-240 mmHg), and two young men performed LIT alone. Training was conducted twice daily for 2 weeks using 3 sets of two dynamic lower body exercises. Quadriceps muscle CSA was measured by magnetic resonance imaging at midpoint of the thigh. Muscle biopsies were obtained from the vastus lateralis (VL) muscle using a needle biopsy. Mean relative change in 1-RM squat strength was 14% in the LIT-KAATSU and 9% in the LIT after two weeks of the training. Mean changes in quadriceps muscle CSA was 7.8% for LIT-KAATSU and 1.8% for LIT. Changes in muscle fiber CSA was 5.9% for type-I and 27.6% (p<0.05) for type-II in the LIT-KAATSU, and -2.1% and 0.5%, respectively, in the LIT. Mean fiber CSA changed 17.0% in the LIT-KAATSU, but not in LIT (-0.4%). We concluded that skeletal muscle and fiber hypertrophy, especially type-II fiber, occur after high frequency KAATSU training.
The purpose of this study was to examine the daily skeletal muscle hypertrophic and strength responses to one week of twice daily KAATSU training, and follow indicators of muscle damage and inflammation on a day-to-day basis, for one subject. KAATSU training resulted in a 3.1% increase in muscle-bone CSA after 7 days of training. Both MRI-measured maximum quadriceps muscle cross-sectional area (Q-CSA max) and muscle volume can be seen increasing after the first day of KAATSU training, and continuously increasing for the rest of the training period. Following 7 days KAATSU resistance training, the increases in Q-CSA max and muscle volume were 3.5% and 4.8%, respectively. Relative strength (isometric knee extension strength per unit Q-CSA max) was increased after training (before, 3.60 Nm/cm2; after, 4.09 Nm/cm2). There were very modest increases in CK and myoglobin after a single bout of KAATSU exercise in the first day of the training, but the values were return towards normal at 2 days after the training. IL-6 remained unchanged throughout the training period. In conclusion, our subject gained absolute strength and increased muscle size after only one week of low intensity KAATSU resistance training. Indicators of muscle damage and inflammation were not elevated by this training. KAATSU training appears to be a safe and effective method to rapidly induce skeletal muscle strength and hypertrophy.
Previous research has shown that high intensity resistance training causes increases in bone density and increases in serum measures of bone turnover like bone-specific alkaline phosphatase (BAP). Medium intensity or low intensity training (like walking) does not result in these changes. However, low intensity training with blood flow restriction (KAATSU) has shown promise in bone and muscle rehabilitation settings. We hypothesized that there would be increases in serum BAP following low intensity KAATSU walk training. Healthy men walked on a treadmill twice per day (at least 4 hours between sessions) for 3 weeks with (KAATSU; n=9) or without (Control; n=9) blood flow occlusion pressure belts on their thighs. After three weeks of training, the KAATSU group experienced significant increases in MRI-measured muscle CSA (P<0.01), 1-RM muscle strength (P<0.01), and serum BAP levels (P<0.05). Percent change in BAP was 10.8% for the KAATSU-walk and 0.3% for the Control-walk. There was no significant change in serum IGF-1 for either group. We conclude that 3 weeks KAATSU walk training increases BAP, a serum marker of bone turnover.