Menstrual state and exercise as determinants of spinal trabecular bone density in female athletes. OBJECTIVE--To study the effects of amenorrhoea and intensive back exercise on the bone mineral density of the lumbar spine in female athletes. DESIGN--Cross sectional study comparing amenorrhoeic with eumenorrhoeic athletes and rowers with non-rowers. SETTING--The British Olympic Medical Centre, Northwick Park Hospital. PATIENTS--46 Elite female athletes comprising 19 rowers, 18 runners, and nine dancers, of whom 25 were amenorrhoeic and 21 eumenorrhoeic. MAIN OUTCOME MEASURE--Trabecular bone mineral density of the lumbar spine measured by computed tomography. RESULTS--Mean trabecular bone mineral density was 42 mg/cm3 (95% confidence interval 22 to 62 mg/cm3) lower in the amenorrhoeic than the eumenorrhoeic athletes; this difference was highly significant (p = 0.0002). Mean trabecular bone mineral density was 21 mg/cm3 (1 to 41 mg/cm3) lower in the non-rowers than the rowers; this was also significant (p = 0.05). There was no interaction between these two effects (p = 0.28). CONCLUSION--The effect of intensive exercise on the lumbar spine partially compensates for the adverse effect of amenorrhoea on spinal trabecular bone density. 