title: Influence of body position on muscle deoxy[Hb+Mb] during ramp cycle exercise.
abstract: 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 (30W/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 deltaV(O)₂/deltaW slope above compared to below gas exchange threshold (GET) for both conditions (upright: 9.8±0.5 vs. 8.2±0.9; supine: 10.7±0.9 vs. 8.0±0.8) and for supine compared to upright cycling above GET. These findings suggest that the supine posture affects O₂ extraction and V(O)₂ kinetics to a greater extent as work rate progresses during ramp incremental exercise.
authors.affiliation: School of Sport and Health Sciences, St. Luke's Campus, University of Exeter, Heavitree Road, Exeter, Devon EX1 2LU, UK.
authors.forename: Fred J
authors.initials: FJ
authors.lastname: DiMenna
authors.forename: Stephen J
authors.initials: SJ
authors.lastname: Bailey
authors.forename: Andrew M
authors.initials: AM
authors.lastname: Jones
mesh_terms: D000328:Adult; D015444:Exercise / Q000502:physiology*; D006454:Hemoglobins / Q000378:metabolism*; D006801:Humans; D008297:Male; D008875:Middle Aged; D018482:Muscle, Skeletal / Q000378:metabolism*; D009211:Myoglobin / Q000378:metabolism*; D010101:Oxygen Consumption / Q000502:physiology*; D011187:Posture / Q000502:physiology; D011659:Pulmonary Gas Exchange; D019265:Spectroscopy, Near-Infrared / Q000379:methods; D013223:Statistics as Topic; D016683:Supine Position / Q000502:physiology; D013997:Time Factors
chemical_list: D006454:Hemoglobins; D009211:Myoglobin; C100003:deoxyhemoglobin