Menstrual Cycle and Training Effects on Physical Work Capacity

The present study examined the effects of women's menstrual cycles on their capacity to perform physical work. Most of the studies of the effects of the menstrual cycle on performance have reported no differences; however, the lack of demonstrated effects could be attributed, in part, to the inability of experimenters to specify the critical phases of the menstrual cycle. The length of the menstrual cycle (between and within subjects) is more variable than commonly expected and this fact, in combination with the inadequacy of current predictors of phase onset, tends to produce error variability in the menstrual cycle independent variable. The present study attempted to overcome the phase specification problem by assessing work capacity of females on alternate days throughout two complete menstrual cycles, thereby avoiding the problem of a priori phase prediction. Physical work capacity was measured in this study by requiring twelve female subjects to cycle to exhaustion on a bicycle ergometer. The results indicated that performance was not affected by the menstrual cycle. A significant training effect was noted during the first menstrual cycle (i.e., performance increased during the cycle); however, performance during the second cycle was lower than during the first cycle. The failure to demonstrate menstrual effects was interpreted as further support for the position that the menstrual cycle does not affect performance. Several hypotheses were offered to account for the training effects.