• Changes in urine levels of F2-isoprostanes [ Designated as safety issue: No ]
  

• Relationships between physiologic pathways that may reduce risk of breast cancer [ Designated as safety issue: No ]
  
• Cumulative incidence of shortened luteal phase length and anovulatory menstrual cycles [ Designated as safety issue: No ]
  
• Comparison of demographic and physiologic predictors of the onset of shortened luteal phase (< 10 days) and/or anovulation [ Designated as safety issue: No ]
  

OBJECTIVES:

Primary

• Compare the changes in urine levels of a stable marker of oxidative stress (F_2-isoprostanes) in healthy young women who undergo exercise training during 4 menstrual cycles vs no exercise.

Secondary

• Assess the changes in other metabolic factors that explain the association between physical activity and breast cancer, including estrogen metabolism (estrone, estradiol, estriol, 2-OHE_1, 2-OHE_2, 2-MeOHE_1, 2-MeOHE_2, 4-OHE_1, 4-OHE_2 [as well as ratios of these metabolites]), insulin-like growth factor (IGF)-1 (as well as IGF-binding proteins-1, -2, and -3), insulin, glucose, insulin resistance, and body composition (including body mass index, lean mass, and body fat [DEXA scan]).
• Determine potential relationships between physiologic pathways that may reduce risk of breast cancer.
• Compare the cumulative incidence of shortened luteal phase length and anovulatory menstrual cycles in these participants.
• Compare demographic and physiologic predictors of the onset of shortened luteal phases (< 10 days) and/or anovulation in these participants.

OUTLINE: This is a randomized, controlled study. Participants are stratified according to baseline body fat percentage and age (18 to 24 years vs 25 to 30 years). Participants are randomized to 1 of 2 intervention arms.

• Arm I: Participants exercise for 30 minutes 5 times a week. The intensity of exercise is increased every 4 weeks. The exercise regimen continues for up to 4 menstrual cycles.
• Arm II: Participants are observed for 4 menstrual cycles. Participants in both arms undergo 24-hour collection of urine on days 7, 8, and 9 of menstrual cycles 1 and 6. F_2-isoprostanes are measured via gas chromatography-mass spectrometry (GC/MS). Estrogens are also measured by GC/MS and include E_1, E_2, E_3, 2-OHE_1, 2-OHE_2, 4-OHE_1, 4-OHE_2, 2-MeE_1, 2-MeE_2, 4-MeE_1, 4-MeE_2, and 16OHE_1.

Participants undergo blood collection, body mass measurement by dual-energy x-ray absorptiometry, and a fitness assessment twice during the 6-month study.

PROJECTED ACCRUAL: A total of 400 participants will be accrued.