Metabolic transitions from rest to high-intensity exercise were divided into two discrete steps (i.e., rest-to-moderate-intensity (R→M) and moderate-to-high-intensity (M→H)) to explore the effect of prior high-intensity ‘priming’ exercise on intramuscular [PCr] and pulmonary V˙O2 kinetics for different sections of the motor unit pool. It was hypothesized that [PCr] and V˙O2 kinetics would be unaffected by priming during R→M exercise, but that the time constants (τ) describing the fundamental [PCr] response and the phase II V˙O2 response would be significantly reduced by priming for M→H exercise. On three separate occasions, six male subjects completed two identical R→M/M→H ‘work-to-work’ prone knee-extension exercise bouts separated by 5min rest. Two trials were performed with measurement of pulmonary V˙O2 and the integrated electromyogram (iEMG) of the right m. vastus lateralis. The third trial was performed within the bore of a 1.5-T superconducting magnet for 31 P-MRS assessment of muscle metabolic responses. Priming did not significantly affect the [PCr] or V˙O2 τ during R→M ([PCr] τ Unprimed: 24±16 vs. Primed: 22±14s; V˙O2 τ Unprimed: 26±8 vs. Primed: 25±9s) or M→H transitions ([PCr] τ Unprimed: 30±5 vs. Primed: 32±7s; V˙O2 τ Unprimed: 37±5 vs. Primed: 38±9s). However, it did reduce the amplitudes of the [PCr] and V˙O2 slow components by 50% and 46%, respectively, during M→H (P<0.05 for both comparisons). These effects were accompanied by iEMG changes suggesting reduced muscle fiber activation during M→H exercise after priming. It is concluded that the τ for the initial exponential change of muscle [PCr] and pulmonary V˙O2 following the transition from moderate-to-high-intensity prone knee-extension exercise is not altered by priming exercise.