Supine lower body negative pressure exercise simulates metabolic and kinetic features of upright exercise

Abstract

Exercise within an artificial gravity environment may help prevent microgravity-induced deconditioning. We hypothesized that supine lower body negative pressure (LBNP) exercise simulates physiological and biomechanical features of upright exercise. Walking (4.5 ± 0.3 km/h) and running (8.0 ± 1.0 km/h) while supine within a LBNP exerciser were compared with walking and running while upright. Eight healthy subjects exercised for 5 min at each of the four posture/gait conditions. LBNP of 52 ± 4 mmHg generated one body weight of supine ground reaction force (GRF). Gait parameters and GRFs were measured during the third minute of exercise, and heart rate and oxygen consumption were measured during the fifth minute. Oxygen consumption during supine LBNP treadmill exercise [walking: 14.6 ± 0.9; running: 32.2 ± 1.6 (SE) ml · min−1 · kg−1] was similar to that during upright treadmill exercise (walking: 15.1 ± 0.9; running: 34.0 ± 1.9 ml · min−1 · kg−1). Heart rate for supine LBNP exercise (grand mean: 133 ± 11 beats/min) was also similar to that for upright exercise (136 ± 11 beats/min). Footward forces integrated over each stride (330.5 ± 34.4 vs. 319.1 ± 29.6 N · s) and rate of force generation (26,483 ± 4,310 vs. 25,634 ± 4,434 N/s) were similar for upright and LBNP exercise, respectively. Our collective results indicate that supine exercise within LBNP can simulate the physiological stress and GRFs that are generated during upright gait.