Introduction & Objective: Women during their lifetime experience a variety of physiological changes that can affect their physiological capacity to perform exercise and induce reduction in achieving the benefits of training. So, finding the best time to perform maximum physical performance is essential. Sports drink consumption can also help to enhance athletic performance. The purpose of this study is to determine the best time to perform the maximum physical performance and the effect of sports drink on exercise capacity in active young women. Materials & Methods: 22 female students with at least 2 years experience in regular aerobic exercise, voluntarily participated in this clinical trial study and were randomly divided into control group (no supplement) and intervention group (drinking sports drink). The physical performance was evaluated in two periods of early and late follicular phases.The data was analyzed by statistical tests and spss16 software. Results: In the early follicular phase compared with the late follicular phase, Vo2max significantly decreased in the control group (P=0.02), There was a significant difference between the two groups in the Vo2max during the early follicular phase (P=0.03). Resting systolic and diastolic blood pressure and heart rate were not significantly different between the groups and different phases (P>0.05). Contrary to the intervention group, the first and third minute recovery heart rates in the control group significantly increased in the early follicular phase compared with the late follicular phase (Respectively, P= 0.016,P=0.043), and compared with the intervention group, the first and third minute recovery heart rates significantly increased during the early follicular phase (Respectively, P= 0.021, P=0.025). Recovery systolic and diastolic blood pressure were not statistically significant between the two groups, and each group in different phases (P>0.05).

Conclusion: Late follicular phase compared to the early follicular phase is the most appropriate time to perform exercise. Sports drink consumption containing 6% carbohydrate during early follicular phase can also improve the physical performance.