The physiologic and metabolic effects of chronic consumption of energy below recommended levels on constant-load exercise was studied in women age 19-24 years. Ten controls (average caloric intake ~ 35 kcal/kg body weight) and 10 subjects with suboptimal energy intake (average caloric intake - 25 kcal/kg body weight) were matched for age, exercise caloric expenditure and percentage of HB-predicted RMR. Subjects (n=20) completed a maximal incremental cycle ergometer test and a 30-minute cycle ergometer test at 75 % of peak oxygen consumption. Although both groups presented a significant increase in ventilation (VE) over time of exercise, the rate of change in VE and end-exercise VE value was significantly greater, F (1 J 18) = 5.63, P < .05, for the suboptimal energy intake group than for the controls. Although not statistically significant (p = 0.454), heart rate (HR) tended to be continuously higher for the suboptimal energy intake group than the control group during the constant-load cycle test. Peripheral ratings of perceived exertion (RPE-L) also tended to be higher for the suboptimal energy intake group at the end of constant-load exercise, however, not significantly (p = 0.072). Two subjects in the suboptimal energy intake group failed to complete the 30-minute submaximal constant-load cycle test; one completed 15 minutes and the other 20 minutes. All subjects in the control group completed the entire submaximal constant-load test (30 minutes). These results suggest that women with chronic suboptimal energy intake have increased difficulty tolerating moderate intensity exercise for 30 minutes (an intensity and duration that mimics a typical exercise session). / Master of Science