Respiratory Muscle Power and the Slow Component of O2 Uptake
Medicine & Science in Sports & Exercise
Purpose: The slow component of O 2 uptake (V O 2sc ) represents a progressive decline in work efficiency during strenuous, constant work rate cycling. Although most of this "excess" O 2 uptake can be explained by factors intrinsic to the exercising muscles, it has been proposed that respiratory muscle work rate may also contribute to the V O 2sc response. To date, however, no study has provided a comprehensive analysis of the mechanical power of breathing (Pb) in relation to the V O 2sc while
... the V O 2sc while performing strenuous exercise. Methods: The mechanical Pb was measured in 12 recreational cyclists (24 T 1 yr, 70.9 T 3.9 kg) during heavy-and severe-intensity cycling. The resistive and elastic components of Pb were quantified using the modified Campbell diagram. Results: Total Pb significantly increased (P G 0.05) over the V O 2sc phase during both heavy ($13 T 2 JImin j1 ) and severe work rate transitions ($219 T 56 JImin j1 ). The magnitude of this increase was relatively greater during severe cycling trials (P G 0.05). The greater "slow component" rise in total Pb during severe work rate transitions was consequent to relatively larger increases in the inspiratory and expiratory resistive Pb and inspiratory elastic Pb (P G 0.05). Conclusions: The findings of this investigation support the thesis that the energetic contribution from respiratory muscles to the V O 2sc amplitude is disproportionately higher during severe-compared with that during heavy-intensity exercise. FIGURE 2-Time-course changes in gas exchange and ventilatory parameters during heavy and severe cycling trials. Values represent mean T SEM. PETCO 2 , end-tidal partial pressure of CO 2 ; V CO 2tot , total pulmonary CO 2 output; V O 2tot , total pulmonary O 2 uptake. *Significantly different from heavy-intensity cycling trial, P G 0.05. †Significantly different from the third minute of constant work rate cycling, P G 0.001. FIGURE 4-Time-course changes in the resistive and elastic components of the Pb during heavy and severe cycling trials. Values represent mean T SEM. *Significantly different from heavy-intensity cycling trial, P G 0.05. †Significantly different from the third minute of constant work rate cycling, P G 0.001.