Reduction in peak oxygen uptake after prolonged bed rest

The purpose was to test the hypothesis that the magnitude of the reduction in peak oxygen uptake (VO2) after bed rest is directly proportional to the level of pre-bed rest peak VO2. Complete pre- and post-bed rest working capacity and body weight data were available from three studies involving 24 men (19-24 yr; peak VO2, 2.39-4.80 l . min-1) and 8 women (23-34 yr; peak VO2 1.47-2.58 l . min-1), who underwent bed rest for 14-20 d with no remedial treatments. Regression analysis of percent change in post-bed rest peak VO2 on pre-bed rest peak VO2 with 32 subjects resulted in correlation coefficients (r) of--0.03 (NS) for data expressed in l . min-1 and -0.17 (NS) for data expressed in ml . min-1 . kg-1. Significant correlations were found that supported the hypothesis only when peak VO2 data were analyzed separately from studies that utilized the cycle ergometer, particularly with subjects in the supine position, as opposed to data obtained from treadmill peak VO2 tests. We conclude that orthostatic factors, associated with the upright body position and relatively high levels of physical fitness from endurance training, appear to increase variability of pre- and particularly post-bed rest peak VO2 data, which would lead to rejection of the hypothesis.