Oxygen uptake as related to work rate increment during cycle ergometer exercise

Summary

We postulated that the commonly observed constant linear relationship between$\dot V_{{\text{O}}_{\text{2}} }$ and work rate during cycle ergometry to exhaustion is fortuitous and not due to an unchanging cost of external work. Therefore we measured$\dot V_{{\text{O}}_{\text{2}} }$ continuously in 10 healthy men during such exercise while varying the rate of work incrementation and analyzed by linear regression techniques the relationship between$\dot V_{{\text{O}}_{\text{2}} }$ and work rate (Δ$\dot V_{{\text{O}}_{\text{2}} }$/ Δwr). After excluding the first and last portions of each test we found the mean ±SD of the δ$\dot V_{{\text{O}}_{\text{2}} }$/ Δwr in ml · min⁻¹· W⁻¹ to be 11.2±0.15, 10.2±0.16, and 8.8±0.15 for the 15, 30, and 60 W·min⁻¹ tests, respectively, expressed as ml·J⁻¹ the values were 0.187±0.0025, 0.170±0.0027 and 0.147±0.0025. The slopes of the lower halves of the 15 and 30 W·min⁻¹ tests were 9.9±0.2 ml·min⁻¹·W⁻¹ similar to the values for aerobic work reported by others. However the upper halves of the 15, 30, and 60 W·min⁻¹ tests demonstrated significant differences: 12.4±0.36 vs 10.5±0.31 vs 8.7±0.23 ml·min⁻¹·W⁻¹ respectively. We postulate that these systematic differences are due to two opposing influences: 1) the fraction of energy from anaerobic sources is larger in the brief 60 W·min⁻¹ tests and 2) the increased energy requirement per W of heavy work is evident especially in the long 15 W·min⁻¹ tests.