Influence of muscle metabolic heterogeneity in determining the VO super( 2p) kinetic response to ramp-incremental exercise

The pulmonary O... uptake (VO...) response to ramp-incremental (RI) exercise increases linearly with work rate (WR) after an early exponential phase, implying that a single time constant (...) and gain (G) describe the response. However, variability in ... and G of VO... kinetics to different step increments in WR is documented. We hypothesized that the "linear" VO...-WR relationship during RI exercise results from the conflation between WR-dependent changes in ... and G. Nine men performed three or four repeats of RI exercise (30 W/min) and two step-incremental protocols consisting of four 60-W increments beginning from 20 W or 50 W. During testing, breath-by-breath VO... was measured by mass spectrometry and volume turbine. For each individual, the VO... RI response was characterized with exponential functions containing either constant or variable ... and G values. A relationship between ... and G vs. WR was determined from the step-incremental protocols to derive the variable model parameters. ... and G increased from 21 plus or minus 5 to 98 plus or minus 20 s and from 8.7 plus or minus 0.6 to 12.0 plus or minus 1.9 ml-min...-W... for WRs of 20-230 W, respectively, and were best described by a second-order (...) and a first-order (G) polynomial function of WR (lowest Akaike information criterion score). The sum of squared residuals was not different (P > 0.05) when the VO... RI response was characterized with either the constant or variable models, indicating that they described the response equally well. Results suggest that ... and G increase progressively with WR during RI exercise. Importantly, these relationships may conflate to produce a linear VO...-WR response, emphasizing the influence of metabolic heterogeneity in determining the apparent VO...-WR relationship during RI exercise. (ProQuest: ... denotes formulae/symbols omitted.)