Several Japanese studies found that blood flow restriction during moderate-intensity resistance training increased strength and muscle mass. Researchers speculated that blood flow restriction caused metabolite buildup and decreased oxygen delivery to the muscles, which stimulated muscle hypertrophy. Limiting oxygen availability during strength training might speed gains in strength and size.
Japanese scientists from the Mie University School of Medicine found that training in a low-oxygen environment promoted muscle hypertrophy and strength. Muscle and strength increased more when training in an altitude chamber (16 percent oxygen, which created a simulated altitude of 7,243 feet), compared to training at sea level.
Living at altitude typically causes muscle atrophy and weight loss because of decreased activity levels and impaired nutrient absorption. Altitude exposure in a chamber is temporary, and allows athletes to train at high altitude without having to live there. Elite endurance athletes often sleep in altitude chambers so that they can “live high and train low.” This is an exciting concept that might have important implications for bodybuilders. (International Journal Sports Physiology Performance, 5: 497-508)