Site-specific differences in the Bone Mineral Density Of Adolescent Sprinters And Long Distance Runners

Abstract

In athletes, exercise does not necessarily increase bone mineral density (BMD). For example, long distance runners (LDR) have been observed to have lower spine BMD compared with nonathletic peers. Spine is non-weight bearing site, and undernutrition and menstrual abnormality of athletes, as commonly demonstrated as female athlete triad, may additively reduce BMD. In contrast, both sprinters (SPR) and LDR mainly use lower limb during exercise. Although spine is still non-weight bearing site for SPR, undernutrition and menstrual abnormality from low energy availability rarely occur in SPR. Therefore, LDR are expected to have lower spine BMD compared with SPR. Although higher muscle mass is associated with increased BMD in general, influence of site-specific differences in muscle mass on BMD remains unclear. PURPOSE: The purpose of this study was to compare individual parts of BMD including spine BMD between LDR and SPR. METHODS: Thirty seven adolescent female LDR and SPR (16.1±0.8 yr old, LDR ( > 800m) n = 16, SPR (100~400m) n = 21) participated in this study. BMD (arms, legs, spine, pelvic and total bone less head; TBLH) and fat-free mass (FFM) were assessed by DXA. Prior stress fracture and menstrual state were asked using questionnaires. Nutrient intake was assessed by food frequency questionnaire. An analysis of covariance was conducted to compare BMD between LDR and SPR controlling for age, BMI, FFM (respective FFM of arms, legs, android, gynoid, and total body), menstrual state, prior stress fracture and vitamin D intake. RESULTS: Spine and TBLH BMD were significantly higher in SPR than LDR (LDR vs. SPR, Spine: 0.94±0.06 vs. 0.99±0.06 g/cm2, TBLH: 0.98±0.06 vs. 1.02±0.05; P <0.05). In the other sites, there was no significant difference between groups. FFM were significant covariate in BMD of all sites except for spine (arms F = 6.86, legs F = 6.73, pelvic F = 10.39, TBLH F = 6.36, P < 0.05). In addition, Vitamin D intake was a significant covariate in pelvic BMD only (F = 6.89, P < 0.05). Moreover, LDR had higher rate of menstrual abnormality (56.3 vs. 23.8%; P < 0.05). CONCLUSION: It was found that spine and TBLH BMD were significantly low in LDR compared with SPR. Although FFM were significant covariate in most of the site specific BMD, group difference in spine BMD could not be explained by either FFM or menstrual state.