Oxygen uptake kinetics in treadmill running and cycle ergometry: a comparison

The purpose of the present study was to comprehensively examine oxygen cons umption ((V)over dot O-2,) kinetics during running and cycling through math ematical modeling of the breath-by-breath gas exchange responses to moderat e and heavy exercise. After determination of the lactate threshold (LT) and maximal oxygen consumption ((V)over dotO(2max)) in both cycling and runnin g exercise, seven subjects (age 26.6 +/- 5.1 yr) completed a series of "squ are-wave" rest-to-exercise transitions at running speeds and cycling power outputs that corresponded to 80% LT and 25, 50, and 75%Delta (Delta being t he difference between LT and ire,,,). iio, responses were fit with either a two- (<LT) or three-phase (>LT) exponential model. The parameters of the i io, kinetic response were similar between exercise modes, except for the (V )over dot O-2, slow component, which was significantly (P < 0.05) greater f or cycling than for running at 50 and 75%Delta (334 +/- 183 and 430 +/- 159 ml/min vs. 205 +/- 84 and 302 +/- 154 ml/min, respectively). We speculate that the differences between the modes are related to the higher intramuscu lar tension development in heavy cycle exercise and the higher eccentric ex ercise component in running. This may cause a relatively greater recruitmen t of the less efficient type II muscle fibers in cycling.