Skeletal muscle adapts to a progressive overload, but the response can vary between different modes and intensities of exercise. Generally, a minimal threshold intensity of 65% of the one repetition maximum (1-RM) is needed to elicit muscle hypertrophy; however, recent studies have challenged this hypothesis and have provided evidence that low-intensity training (LIT) combined with vascular restriction (KAATSU) may also elicit increases in muscle size and strength. The physiological aspects of applying vascular restriction during exercise are not fully understood and may be explained by several factors. Examining the results of previous studies may help elucidate the factors responsible for the adaptations associated with vascular restriction in humans. Therefore, the objectives of this review are to summarize current knowledge regarding the physiological adaptations of skeletal muscle after low-intensity exercise combined with vascular restriction, the different training protocols used to elicit adaptations, and suggested areas for future research.
Purposes: The KAATSU training is performed under the reduction of muscle blood flow by a specially designed belt (KAATSU belt), which induces blood pooling in capacitance vessels by restricting venous return. However, no prior studies have examined the effects of KAATSU training on haemostasis. The purpose of the present study was to investigate acute effects of KAATSU training on haemostasis including fibrinolytic responses in healthy subjects. Methods: Two protocols have been performed. (1) 6 healthy men (mean age= 48 ± 5 yr) performed KAATSU (160 mmHg) of both thighs for 15 minutes and then KAASTU training combined with low-intensity leg and foot aerobic exercises for ∼ 10 minutes in hypobaric chamber, which mimics 8000 feet in airflight. (2) Another 7 men (mean age=30 ± 4 yr) performed leg press exercises (30 % 1 RM) with and without KAATSU of both thighs 24 h after bed rest. Blood samples were taken at rest, immediately after KAATSU, and exercises with or without KAATSU, and after exercise. For the investigation of blood fibrinolysis, determinations of tissue-type plasminogen activator (tPA) activity or antigen, plasminogen activator inhibitor (PAI)-1 activity or antigen, fibrin degradation product (FDP) and D-dimer were used. Prothrombin time (PT) and platelet counts were also measured. Results: (1) In hypobaric chamber, KAATSU by itself significantly increased tPA activity, while PAI-1 activity was unchanged. Furthermore, immediately after the exercise, tPA activity increased significantly. (2) During the exercises combined with KAATSU 24 h after bed rest, tPA antigen significantly increased, compared with control exercises, but PAI-1 antigen was unchanged. In both cases, KAATSU training did not induce fibrin formation as assessed by fibrin D-dimer and FDP. Conclusions: This study indicates that potentially favorable changes occur in fibrinolytic factors after KAATSU and KAATSU training in healthy subjects.