A.J. Seipel, C.B. Jones, J.T. Penry

Oregon State University, Corvallis, OR

Direct measurement of oxygen consumption (V̇O2) during a maximal graded exercise (GXTmax) test remains the gold standard for assessing cardiorespiratory fitness. However, the validity of these tests may be compromised in individuals do not achieve a maximal plateau in V̇O2 (V̇O2max). One explanation is these individuals may be working in the severe intensity domain, during submaximal workloads. PURPOSE: To consider the role of high intensity exercise tolerance on V̇O2max measurement, examining the relative contributions of critical speed (CS) and the curvature constant of the speed-time to exhaustion relationship (D’). METHODS: Thirty individuals (n = 30; 15 male, 15 female) of varied running experience completed this study. Each subject performed one treadmill GXTmax and six runs to volitional exhaustion (90 seconds – 12 minutes duration) in randomized order over three visits. Multiple regression analysis was performed with V̇O2max as the dependent variable, while CS and D’ were set as predictor variables. The relative contribution of both CS and D’ was quantified by squared semipartial correlations. To confirm fatigue in subsequent runs did not impact CS-D’ measurement, the magnitude of participant’s individual trial D’ residuals were compared using mixed-effects modelling with a random intercept for each participant and a random slope for day. RESULTS: Both CS and D’ contributed significantly to variance observed in V̇O2max (sr2 = 0.803 and 0.095, respectively; p < 0.01), with overall R2 = 0.828. The mixed-effects modelling did not reveal any significant differences for day or trial D’ residual values (p > 0.05). CONCLUSION: The strong CS-V̇O2max relationship was expected, as both measures are dependent on similar physiological measures. The D’-V̇O2max relationship may be due to the effect of the V̇O2 slow component in restoring D’. Conversely, D’ may serve a protective role against the effects of fatigue-inducing metabolites; thus, having a D’ reserve would allow a subject to continue longer during a GXTmax. Overall, these data suggest that measuring CS and D’ can serve as a proxy to V̇O2max when assessing cardiorespiratory fitness. Alternatively, when V̇O2 data are relevant, test administrators should design protocols to avoid depleting D’ at submaximal workloads, while still allowing V̇O2 to stabilize.

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