Constructing quasi-linear Vo^sub 2^ responses from nonlinear parameters

Oxygen uptake (VO2) kinetics have been shown to be governed by a nonlinear control system across a range of work rates. However, the linearity of the VO2 response to ramp incremental exercise would appear to be the result of a linear control system. This apparent contradiction could represent a balancing of changing VO2 kinetics parameter values across a range of work rates. To test this, six healthy men completed bouts of ramp incremental exercise at 15, 30, and 60 W/min (15R, 30R, 60R, respectively) and four bouts of an extended-step incremental exercise. VO2 parameter values were derived from the step exercise using two monoexponential models: one starting at time zero and encompassing the entire stage (MONO), and the other truncated to the first 5 min and allowing a time delay (5TD). The resulting parameter values were applied to an integrative model to estimate the ramp responses. As work rate increased, gain values increased (P < 0.001 for MONO and 5TD), as did mean response time (or time constant) values (MONO: P< 0.001; 5TD: P = 0.003). Up to maximal VO2 (VO2 max), the gains of the estimated ramp responses from both models were not different from the gains of the actual observed VO2responses for 15R and 30R (15R: 11.3 ± 1.2, 11.7 ± 0.7, 10.9 ± 0.3; 30R: 10.5 ± 0.8, 11.0 ± 0.5, 10.7 ± 0.3 ml O2...min...1...W...1, for actual, MONO, 5TD, respectively) but were significantly greater for 60R (8.7 ± 1.0, 9.9 ± 0.4, 10.3 ± 0.3 ml O2...min-1...W-1 for actual, MONO, 5TD, respectively). Up to 80% VO2 max gain values were not significantly different for any ramp rate (P > 0.05 for all). We conclude that the apparent linearity of the VO2 response to ramp incremental exercise is consequent to a balancing of increasing time constant and gain parameter values. (ProQuest: ... denotes formulae/symbols omitted.)