The y-intercept of the critical power function as a measure of anaerobic work capacity

Abstract

When bouts of muscular work are performed to exhaustion at different intensities, the slope of the regression of maximal work (work limit) on maximal time (time limit) is referred to as critical power (CP). The y-intercept of this function is considered to represent anaerobic work capacity (AWC). The purpose of this investigation was to examine the relationship between the y-intercept from the critical power curve and measures of AWC (total work accomplished, maximal blood lactate and post-exercise venous blood pH) gained from repeated, maximal exercise. Nine male volunteers of moderately high training status ([Vdot]O₂max 4·45 ±0·251/min) completed three cycle ergometer tests to exhaustion (at 300, 350 and 400 W) for the determination of CP. A second cycle ergometer task involved repeated maximal effort (against 0075N/kg body mass) over five 1 min periods. Five min of passive recovery separated each exercise bout, at the end of which capillary blood was collected for lactate analysis. On completion of the fifth bout, venous blood was sampled for the determination of blood pH. Total accumulated work provided a performance estimate of AWC which, together with blood lactate and pH, was compared to the y-intercept. Correlation analysis revealed a significant relation between the y-intercept and total work accomplished (r=0·74; p<0·05), while post-exercise venous blood pH was positively related to both the y-intercept (r7equals;0·92; p<0·01) and the accumulated work recorded (r=0·92; p<0·01). No significant correlation between peak blood lactate and work was found (r=0·16; ns), although a relation between post-exercise venous blood pH and [Vdot]O₂max was established (r=0·84; p <0·05). The capacity for high intensity interval work was well represented by the y-intercept in active males. Furthermore, the relations between blood pH and both the y-intercept and accumulated work suggest that either improved buffering or a greater contribution of aerobic metabolism to the energy yield may have been responsible for the more successful performances in the interval exercise.

Keywords:

• Critical power
• Anaerobic work capacity
• Bicycle ergometry test
• Exercise test