Shelden, M. A., Vardaxis, V. G., Rivera, J., Boley, B., A., & Weir, J. P. (2011). Lack of association between changes in running mechanics and the VO2 slow-component. Medicine and Science in Sports and Exercise, 43(5). Supplement abstract 1664.

"An oxygen consumption (VO2) steady state is not reached during high-intensity exercise. Instead, VO2 drifts upward over time even if exercise intensity (e.g., running speed) is constant. This drift is termed the VO2 slow-component. Changes in mechanical efficiency with fatigue may explain the VO2 slow-component."

This study examined the relationship between changes in running mechanics and oxygen consumption during constant speed running in 18 Ss. After a familiarization session, Ss performed a treadmill test to exhaustion (1% grade, speed increment of 0.5 mph per minute). On another day, Ss performed a constant-speed treadmill run at a speed midway between the ventilatory threshold and the respiratory compensation threshold. Gas exchange data were continuously recorded. 3-D kinematic data were captured over 10 seconds every 30 seconds. Total mechanical energy was calculated using the no transfer approach for a 13 segment anthropometry model. After removing the first minute of the run data, both VO2 and total mechanical energy were regressed against time within each S.

The mean total mechanical energy slope was not significant while the mean VO2 slope was significantly greater than zero. The correlation between the total mechanical energy and VO2 slopes was not significant. The high-intensity runs resulted in a significant slope for oxygen consumption, indicating the presence of the VO2 slow-component. However, the mean total mechanical energy slope was not significantly different from zero, so that despite the steady increase in oxygen consumption, there was not a concomitant change in running mechanics.

Implication. Oxygen consumption increases during high-intensity exercise are not driven by changes in total mechanical energy.

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