Relationship Between Exercise Training-induced Changes In Oxygen Uptake Kinetics And The Power-duration Relationship

PURPOSE: We aimed to determine the relationships between training-induced changes in the parameters of the power-duration relationship (critical power and W′) and those of pulmonary oxygen uptake (V̇O2) kinetics (the fundamental phase time constant; t0.63, and the slow component; V̇O2sc). A theoretical model of the human skeletal muscle bioenergetic system was employed to elucidate the biochemical mechanisms underpinning the training-induced changes. METHODS: Eleven healthy untrained males underwent 2 weeks of severe-intensity exercise training. Before and after training, V̇O2max was assessed via an incremental exercise test on a cycle ergometer, CP and W′ were assessed via constant power determination trials, and V̇O2 kinetics were assessed during exercise at a PO 10% above CP (post-training at the same absolute and relative intensity as pre-training). A previously described and validated computer model of the human skeletal muscle bioenergetic system was used to provide further insight into training-induced changes. RESULTS: CP and t0.63 were strongly inversely correlated before (r = -0.76, P = 0.0069) and after (r = -0.79, P = 0.0042) training, and their training-induced changes were also correlated (r = -0.69, P = 0.020). Computer simulations suggested that increased oxidative phosphorylation activity (kOX) was the main factor determining the training-induced changes in CP and t0.63. W′ was increased by training (PRE: 19.2 ± 7.0 kJ, POST: 23.3 ± 5.0 kJ; P = 0.017), and was inversely correlated with the rate of development of the V̇O2sc both before (r = -0.64, P = 0.032) and after (r = -0.74, P = 0.0086) training. Model simulations suggested that variations in kOX, the accessible phosphate (+creatine) pool (Pacc), and the peak inorganic phosphate (Pi) concentrations attained prior to task failure (Pipeak) could explain the observed training-induced alterations in W′ and the V̇O2sc. CONCLUSION: The present study provides strong evidence that the bioenergetic mechanisms underpinning the parameters of the power-duration relationship and V̇O2 kinetics are similar, demonstrating that these in vivo physiological variables arise as a consequence of underlying biochemical parameters, such as kOX, Pacc, and Pipeak.