Influence of priming exercise on pulmonary O₂ uptake kinetics during transitions to high-intensity exercise from an elevated baseline

It has been suggested that the slower O 2 uptake (V̇o 2 ) kinetics observed when exercise is initiated from an elevated baseline metabolic rate are linked to an impairment of muscle O 2 delivery. We hypothesized that “priming” exercise would significantly reduce the phase II time constant (τ) during subsequent severe-intensity cycle exercise initiated from an elevated baseline metabolic rate. Seven healthy men completed exercise transitions to 70% of the difference between gas exchange threshold (GET) and peak V̇o 2 from a moderate-intensity baseline (90% GET) on three occasions in each of the “unprimed” and “primed” conditions. Pulmonary gas exchange, heart rate, and the electromyogram of m. vastus lateralis were measured during all tests. The phase II V̇o 2 kinetics were slower when severe exercise was initiated from a baseline of moderate exercise compared with unloaded pedaling (mean ± SD τ, 42 ± 15 vs. 33 ± 8 s; P < 0.05), but were not accelerated by priming exercise (42 ± 17 s; P > 0.05). The amplitude of the V̇o 2 slow component and the change in electromyogram from minutes 2 to 6 were both significantly reduced following priming exercise (V̇o 2 slow component: from 0.47 ± 0.09 to 0.27 ± 0.13 l/min; change in integrated electromyogram between 2 and 6 min: from 51 ± 35 to 26±43% of baseline; P < 0.05 for both comparisons). These results indicate that the slower phase II V̇o 2 kinetics observed during transitions to severe exercise from an elevated baseline are not altered by priming exercise, but that the reduced V̇o 2 slow component may be linked to changes in muscle fiber activation.