Selection of a Fifteen-Minute Work Load on a Treadmill and Bicycle

Abstract

Four male and four female subjects were asked to select work loads on a treadmill and on a bicycle that would exhaust them if they carried out the exercise for 15 min. Heart rate, oxygen uptake, and blood samples were examined during and following the exercise to determine if any internal mechanism was informing the subject of his capability to exercise. Subjects all selected work efforts that were similar with respect to heart rate levels, energy cost, oxygen debts, and ventilation measurements when the bicycle and treadmill exercises were compared. Blood ph and HCO₃ levels were only slightly affected by the exercise loads chosen by the women, while the men showed slight metabolic acidosis with work levels selected. Men chose work levels that resulted in heart rates and RQ measurements similar to the women's, while energy levels and debts were twice the level of the female subjects. The most consistent cue, regardless of sex or type of exercise, was a heart rate level of between 165 and 180 and RQ of .90. The work level selected by all subjects was carried out for 15 min. with only slight increases in measurements between the first and last minutes. All subjects felt they had selected the highest work levels they were able to do.