LOW OR NORMAL BONE MINERAL DENSITY IN FEMALE ELITE TRIATHLETES

Abstract

Our hypothesis was that bone mineral density (BMD) is correlated to maximal muscle strength (MMS) and sex hormone concentrations in female elite triathletes, but not in sedentary females. Prevalence of the female athlete triad (low BMD menstrual disturbances and eating disorders) was also evaluated. Subjects were eight elite triathletes (training 8–24 hrs/wk) and seven sedentary controls (training < 4 hrs/wk), age 21–37 years. Regional and total BMD (g/cm2) were measured by DXA. MMS was measured as isokinetic peak torque (Nm) in hip extension, -flexion and knee extension. Progesterone (P), estrogen, osteocalcin, CrossLaps (CL) and vitamin D were measured. Subjects reported menstrual status. In triathletes eating disorders and food intake was evaluated by questionnaire/interview. One triathlete had Bulimia Nervosa, amenorrhea and osteopenia/osteoporosis in non-weight bearing bones (NWB) (76–88% of normal). Two triathletes had risk behaviour related to eating disorders and a daily energy deficit (31% and 35%), one with osteopenia in distal radius. Compared to controls, triathletes did not have a higher BMD, and BMD in NWB tended to be lower (significant only in left distal radius (p < 0.05). In triathletes BMD in weight bearing bones (WBB) (femur and wards) and total BMD correlated to peak torque in hip flexion (0.70 < r < 0.86, p < 0.01), and BMD L2-L4 correlated to CL concentration (r = −0.70, p < 0.05). In the whole group BMD in NWB (L2-L4 and right distal radius) correlated to P concentration (0.48 < r < 0.51, p < 0.05). Conclusion: Despite a high training volume triathletes had the same BMD in WBB as sedentary controls, in NWB BMD seemed to be compromised. A part from the negative correlation between CL concentration and BMD L2-L4 in triathletes biological bone markers gave no indications that the relative low BMD was due to changes in remodeling. From the present results it seems that low P concentration exerts a negative effect primarily in NWB, whereas impact loading and muscle strength counteract this effect in WBB.