Ventilation (V̇E), CO2 output (V̇CO2), oxygen uptake (V̇O2), respiratory exchange ratio (R), and the ventilatory equivalents for V̇O2 and V̇CO2 were measured during graded exercise before and after 10 d of continuous bed rest (BR) in the -6° headown position to determine the effect of deconditioning on the anaerobic threshold (AT), i.e., the highest workrate or V̇O2 which was achieved without evidence of lactic acidosis, as judged from the profile of ventilatory and gas exchange responses. Ten healthy male subjects performed a supine graded cycle ergometer test before (pre) and after (post) BR which consisted of 4 min of unloaded pedaling at 60 rpm followed by an increased workrate of 15 W · min-1 until volitional fatigue (max). V̇E, V̇CO2, V̇O2, R, V̇E/V̇O2 and V̇E/V̇CO2 were measured every 30 s and used collectively to identify the AT. Plasma (PV) and blood (BV) volumes were measured pre- and post-BR by T-1824. Following BR, V̇O2max decreased from 2.42±0.17 to 2.25±0.13 L · min-1 (7.0%, p < 0.05). BR significantly (p < 0.05) reduced at AT from 1.26±0.09 to 0.95±0.05 L · min-1 V̇O2; from 52.2±2.0 to 42.6±1.6% V̇O2max; and from 93±9 to 65±6 W. A correlation coefficient (r) of -0.11 (NS) was found between the change in V̇O2max and change in AT. A decrease in BV of 8.8% (p < 0.05) was due to the 11.0% reduction in PV; red cell volume remained constant. The change in AT following BR was significantly (p < 0.05) correlated with the changes in BV and PV (r =+0.73 and +0.80, respectively). These data suggest that: the reduction in AT induced by BR deconditioning cannot be completely explained by the reduction in V̇O2max; the change in AT following BR is manifested by a decrease in both absolute and relative workrate; and the decrease in AT is associated with the reduction in intravascular fluid volume.
|Original language||English (US)|
|Number of pages||7|
|Journal||Aviation Space and Environmental Medicine|
|State||Published - 1986|
ASJC Scopus subject areas
- Public Health, Environmental and Occupational Health