It has been suggested that skeletal muscle oxygen uptake (VO₂) kinetics follow a first-order control model. Consistent with that, VO₂ should show both: 1) similar onset kinetics and 2) an on-off symmetry across submaximal work intensities regardless of the metabolic perturbation. To date, consensus on this issue has not been reached in whole body studies due to numerous confounding factors associated with O₂ availability and fiber type recruitment. To test whether single myocytes demonstrate similar intracellular PO₂ (P_IO₂) on- and off-transient kinetics at varying work intensities, we studied Xenopus laevis single myocyte (n=8) P_IO₂ via phosphorescence quenching during 2 bouts of electrically-induced isometric muscle contractions of 200 (low; L) and 400 (high; H) ms contraction duration (1 contraction every 4 s, 15 min between trials, order randomized). The fall in P_IO₂, which is inversely proportional to the net increase in VO₂, was significantly greater (p<0.05) during the H (24.1±3.2) vs. L (17.4±1.6 mmHg) contraction bout. However, the mean response time (MRT; time to 63% of the overall change) for the fall in P_IO₂ from resting baseline to end-contractions was not different (H, 77.8±11.5 vs. L, 76.1±13.6 s; p>0.05) between trials. The initial rate of change at contraction onset, defined as delta P_IO₂/MRT, was significantly greater (p<0.05) in H compared with L. The P_IO₂ off-transient MRT from the end of the contraction bout to initial baseline was unchanged (H, 83.3±18.3 vs. L, 80.4±21.6 s; p>0.05) between H and L trials. These data revealed that P_IO₂ dynamics in frog isolated skeletal myocytes were invariant despite differing contraction durations and, by inference, metabolic demands. Thus, these findings demonstrate that mitochondria can respond more rapidly at the initial onset of contractions when challenged with an augmented metabolic stimulus in accordance with an apparent first-order rate law.