Primary Outcome Measures:
- Bone density [ Time Frame: 3 months ]
Secondary Outcome Measures:
- Energy availability [ Time Frame: 3 months ]
The purpose of this project is to examine the relationships among low energy availability, H-P-A axis, menstrual function and bone density and bone turnover in high school female cross country runners. Our objectives are to: 1)determine energy intake, exercise energy expenditure, and fat-free mass to examine energy availability; 2)in a subset of runners, using double labelled water, estimate total energy expenditure and indirect calorimetry to estimate resting metabolic rate; 3)assess the relationship between energy availability, hormones that regulate bone turnover, markers of bone formation and resorption and bone mineral content and density; 4)identify the relationship between energy availability, hormones that regulate menstrual function and current menstrual status; and 5)determine the energy intake and energy expenditure variables exhibiting the strongest associations with energy availability.