The metabolic profiles of different fiber type populations under the emergence of the slow component of oxygen uptake.

To investigate the influence of different metabolic muscle fiber profiles on the emergence of the slow component of oxygen uptake ($${\dot{\text{V}}\text{O}}_{2}$$SC), 12 habitually active males completed four sessions of different combinations of work-to-work transition exercises up to severe intensity. Each transition was modeled to analyze the different kinetic parameters. Using a new approach, combining Henneman’s principle and superposition principle, a reconstructed kinetics was built by temporally aligning the start of each new transition and summing them. The primary phase time constant significantly slowed and the gain at the end (GainEnd) significantly increased when transitions started from a higher intensity (p < 0.001). Kinetic parameters from the reconstructed curve ($${\dot{\text{V}}\text{O}}_{2} {\text{baseline}}$$, time delay of primary phase, $${\dot{\text{V}}\text{O}}_{2}$$End and GainEnd) were not significantly different from one transition to severe exercise. These results suggest that the appearance of the $${\dot{\text{V}}\text{O}}_{2}$$SC is at least related to, if not the result of, the different metabolic properties of muscle fibers.