Influence of initial metabolic rate on pulmonary O(2) uptake on-kinetics during severe intensity exercise

Abstract

We hypothesised that the fundamental (Phase II) component of pulmonary oxygen uptake ( [Formula: see text] ) kinetics would be significantly slower when step transitions to severe intensity cycle exercise were initiated from elevated baseline metabolic rates, and that this would be associated with evidence for a greater activation of higher-order (i.e. type II) muscle fibres. Seven male subjects (age 22-34 years) completed repeat step transitions to a severe (S) work rate, estimated to require 100% [Formula: see text] peak, from a baseline of: (1) 3min of unloaded cycling (L-->S); (2) 6min of moderate exercise (M-->S); (3) 6min of heavy exercise (H-->S). Pulmonary gas exchange and the electromyogram (EMG) of the m. vastus lateralis were measured throughout all exercise tests. The Phase II [Formula: see text] kinetics became progressively slower at higher baseline metabolic rates (tau was 37+/-6, 59+/-23, and 93+/-50s for L-->S, M-->S, and H-->S, respectively; PS and H-->S). Both the integrated EMG and the mean power frequency were significantly higher immediately before the step transition to severe exercise when it was initiated from higher metabolic rates. Although indirect, these data suggest that the slower Phase II [Formula: see text] kinetics observed at higher baseline metabolic rates was related to alterations in muscle activation and fibre recruitment patterns