BMD in elite female triathletes is related to isokinetic peak torque without any association to sex hormone concentrations.

AIM: Female endurance athletes suffering from low energy availability and reproductive hormonal disorders are at risk of low BMD. Muscle forces acting on bone may have a reverse site-specific effect. Therefore we wanted to test how BMD in female elite triathletes was associated to isokinetic peak torque (IPT) and reproductive hormone concentrations (RHC). A possible effect of oral contraceptives (OCON's) is taken into consideration.

METHODS

Eight female elite triathletes (training 8-24 hrs/wk) and seven sedentary controls, age 21-37 years, participated. Total body and regional BMD (g.cm-2) were measured by DXA. IPT were measured during knee extension, and trunk extension and flexion (Nm). Serum RHC and biochemical bone markers were evaluated. Energy balance was estimated from 7-days training-and weighed food records.

RESULTS

Despite a high training volume, BMD in triathletes was not higher than in controls. In triathletes trunk flexion IPT, but not RHC, was a strong predictor of BMD in both total body and femur (0.70<r<0.86, P<0.05). RHC did not differ between triathletes and controls, but in OCON-users RHC (in controls also BMD) seemed lower than in non-users. Energy intake in triathletes corresponded to 65-111% of energy expenditure.

CONCLUSION

The association between trunk flexion IPT and BMD in triathletes supports the theory that muscle forces are important osteogenic factors. The findings of no correlation between RHC and BMD, but a tendency to a negative effect of low RHC only in OCON-controls, might indicate that in female athletes muscle forces acting on bone potentially counteract a negative effect of reproductive hormonal disorders on BMD.