The Effect of Vitamin D Supplementation on Muscle Power in Elite Cyclist

The purpose of this study is to evaluate the change in vitamin D status with the change in muscular strength and muscular power in highly trained athletes over a 9-month study period. The investigators hypothesize that the greatest muscular strength and power gains will be demonstrated in the athletes who achieve and maintain a 25(OH)-D \> 50 ng/mL (but \ 50 ng/mL is associated with improved muscular power by assessing specific performance measures (e.g. Vertical Jump Test and Wingate test) relative to lean body mass; and Aim 2. to examine the correlation between vitamin D status and muscular power over time.