Influence of body position on muscle deoxy[Hb plus Mb] during ramp cycle exercise

We used near-Infrared spectroscopy (NIRS) to test the hypothesis that body position alters the sigmoidal response profile of muscle fractional O-2 extraction (estimated using deoxy[Hb + Mb]) during incremental cycle exercise Seven male subjects (mean +/- SD age 32 +/- 13 years) completed a ramp incremental cycling test to exhaustion (30 W/min) in both the supine and upright body positions The sigmoidal (as opposed to hyperbolic) model that provided the better fit to deoxy[Hb + Mb] data during upright cycling was also present for the supine response, however, the slope of the sigmoid was increased (upright 0.052 +/- 0 012 vs supine 0 090 +/- 0.036% %P-peak(-1); P < 0 05) and a plateau occurred at a lower work rate (upright 83 +/- 8 vs supine 68 +/- 19%P-peak(-1); P < 0 05) during supine exercise These changes occurred in the absence of a leftward shift of the sigmoid We also found a significantly greater Delta V-O2/Delta W slope above compared to below gas exchange threshold (GET) for both conditions (upright 9.8 +/- 0 5 vs 82 +/- 09; supine 107 +/- 09 vs 80 +/- 0.8) and for supine compared to upright cycling above GET These findings suggest that the supine posture affects O-2 extraction and V-O2 kinetics to a greater extent as work rate progresses during ramp incremental exercise (C) 2010 Elsevier B V All rights reserved