Leg electromyography and the VO2-power relationship during bicycle ergometry

The relationship between oxygen consumption and power is not linear. The purpose of this investigation was to examine the nature of the relationship and the cause of the nonlinearity.

Eight male cyclists (60.5 +/- 3.8 mL O2.min-1.kg(-1) VO2 peak) completed an incremental exercise test (1 W.5 s(-1)) to exhaustion. VO2 was measured every breath, and rmsEMG was recorded continuously over the belly of vastus lateralis, biceps femoris, and lateral gastrocnemius.

VO2 is a linear function of power in moderate exercise; the slope of the linear portion was approximately 9.7 mL O2.min(-1).W(-1), which is consistent with the steady state gain for moderate exercise. Beyond this initial break from linearity, the VO2.W(-1) plot demonstrates a second break that is not different from the point of respiratory compensation (break in VE.VCO2(-1)). These breaks were coincident with increased neuromuscular activity (1st break: 194 +/- 27 W for VO2, 191 +/- 25 W for vastus lateralis; 2nd break: 262 +/- 34 W for VO2, 258 +/- 27 W for vastus lateralis) and corresponded to approximately 58% VO2 peak for the first and 75% VO2 peak for the second break.

VO2 is not a linear function of power. During an incremental test, neuromuscular activity and VO2 increase more rapidly in heavy exercise. Both VO2 and neuromuscular activity exhibit a second break at very high power output, which may mark an upper limit for sustainable exercise.