The exercising female with nutritional deficits and related menstrual irregularities is at risk of compromising long-term bone health, i.e. Female Athlete Triad. There is no animal model of the Female Athlete Triad. The purpose of this study was to examine long-term energy restriction in voluntary wheel running female rats on estrous cycling, bone mineral content, and leptin levels. Twelve female Sprague Dawley rats (age=34 days) were fed ad-libitum and access to running wheels during an initial 14-week period, providing baseline and age-related data. Daily collection included dietary intake, body weight, estrous cycling and voluntary running distance. At 4 months, rats were randomized into two groups, 6 restrict-fed (70% of ad-lib intake) and 6 continued as ad libitum-fed controls. Energy intake, energy expenditure, and energy availability (energy intake - energy expenditure) were calculated for each animal. Serum estradiol and leptin concentrations were measured by RIA. Femoral and tibial bone mineral density (BMD) and bone mineral content (BMC) were determined by dual energy x-ray absorptiometry (DXA). Restrict-fed rats exhibited a decrease in energy availability during Weight Loss and Anestrous phases (p=0.002). Compared to controls after 12 weeks, restrict-fed rats showed reduced concentrations of serum estradiol (p=0.002) and leptin (p=0.002), lower ovarian weight (p=0.002), and decreased femoral (p=0.041) and tibial (p=0.05) BMC. Decreased energy availability resulted in anestrous, and significant decreases in BMC, estrogen and leptin levels, and body weight. Finally, there is a critical level of energy availability to maintain estrous cycling.