K. Fisher, E. Flood, S. Alvord, D. Dougherty, K. Frein, B.W. Wilkins

Gonzaga University, Spokane, WA.

Females exhibit greater type I muscle fiber distribution and higher muscle capillarization, both of which may lead to enhanced oxidative metabolic ability. Critical power (CP) is a measure of the highest, sustainable, steady state rate of oxidative metabolism. PURPOSE: This study, therefore, aimed to explore if a fundamental difference in CP exists between males and females. METHODS: Eleven subjects (6 men/5 women) aged 20.7±1.1 yr. participated in three study days. Subjects completed a graded exercise test on a cycle ergometer to determine maximal oxygen uptake, a three-minute all-out test (3MT) on a cycle ergometer to estimate CP using end test power (ETP), and four 5-minute exercise trials of wattage-controlled cycling to predict CP using a novel muscle oxygenation zero-slope method. Female subjects were tested during the early follicular phase (during menstruation) of their menstrual cycle. Muscle oxygenation (forearm and thigh) and oxygen uptake were continuously measured throughout each exercise session and venous blood lactate was assessed before and after exercise trials. Body composition was determined via skin folds (4 site) to determine fat free mass (FFM). RESULTS: Male subjects had more FFM (70.8±8.8 kg) compared to female subjects (49.3±2.2 kg; p=0.001) and a greater ETP (223±37 W for males, 180±41 W for females) estimated from the 3MT. Muscle oxygenation zero-slope estimates of CP were greater for male (203±39 W) compared to female (174±55 W) participants. When controlling for FFM, ETP for male subjects was 3.2±0.6 W/kg and 3.6±0.7 W/kg for female subjects (p=0.285) and estimated CP from the zero-slope method was 2.9 W/kg ± 0.7 W/kg for male subjects and 3.5±1.0W/kg for female subjects (p=0.265). CONCLUSIONS: Male participants demonstrated a higher estimated CP compared to female participants independent of measurement method, either ETP via 3MT or the novel zero-slope method. However, when expressed relative to FFM the sex differences in CP disappear and women tended to have a higher CP than their male counterparts, although higher statistical power is needed to determine if significant differences exist.


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