Validity of the oxygen uptake efficiency slope to assess aerobic fitness following bed rest

Abstract

Achieving true peak oxygen uptake (VO2peak) is often difficult after the deconditioning that results from musculoskeletal unloading via bed rest or spaceflight. Consequently, submaximal measures predicting VO2peak are crucial for the effective assessment of cardiorespiratory functional reserve. One proposed index, oxygen uptake efficiency slope (OUES), is effort independent; however, its sensitivity to change in aerobic performance because of disuse and exercise training is unknown. Twenty‐five subjects performed a maximal exercise test before and after 14 days of 6° head‐down tilt bed rest. During bed rest, 9 subjects completed a high‐intensity exercise program (EX) while 16 were sedentary (CONT). In addition to VO2peak and ventilatory threshold (VT), OUES at 75% and 100% of total exercise time were determined. VO2peak (−13%), VT (−17%), OUES100 (−12%), and OUES75 (−10%) decreased in the CONT group; while VO2peak (+10%), VT (+8%), OUES100 (+6%), and OUES75 (+10%) increased in the EX group. The change in both OUES100 and OUES75 was significantly related to the change in VO2peak (OUES100: r = 0.85; OUES75: r = 0.75; P < 0.05). Bland‐Altman plots showed high agreement between OUES and VO2peak. These findings indicate that OUES is an objective submaximal index that can detect changes in cardiopulmonary reserve following deconditioning and exercise training.Support: NASA Johnson Space Center Human Research Program