Upright exercise or supine lower body negative pressure exercise maintains exercise responses after bed rest

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Abstract
Upright exercise or supine lower body negative pressure exercise maintains exercise responses after bed rest. Med. Sci. Sports Exerc., Vol. 29, No. 7, pp. 892-900, 1997. Adaptation to bed rest or space flight is accompanied by an impaired ability to exercise in an upright position. We hypothesized that a daily, 30-min bout of intense, interval exercise in upright posture or supine against lower body negative pressure (LBNP) would maintain upright exercise heart rate and respiratory responses after bed rest. Twenty-four men (31 ± 3 yr) underwent 5 d of 6° head-down tilt: eight performed no exercise (CON), eight performed upright treadmill exercise(UPex), and eight performed supine treadmill exercise against LBNP at -51.3± 0.4 mm Hg (LBNPex). Submaximal treadmill exercise responses (56, 74, and 85% of ˙VO2peak) were measured pre- and post-bed rest. In CON, submaximal heart rate, respiratory exchange ratio, and ventilation were significantly greater (P ≤ 0.05) after bed rest. In UPex and LBNPex, submaximal exercise responses were similar pre- and post-bed rest. Our results indicate that a daily 30-min bout of intense, interval upright exercise training or supine exercise training against LBNP is sufficient to maintain upright exercise responses after 5 d of bed rest. These results may have important implications for the development of exercise countermeasures during space flight.