Medicine & Science in Sports & Exercise:
H-13E Free Communication/Slide Mechanics of Bone and Connective Tissue
Macdonald, H M.1; MacKelvie, K J.1; MacLean, L B.1; McKay, H A.1
1University of British Columbia, Vancouver, British Columbia
We have previously shown that girls who participated in a 20-month school-based exercise intervention gained approximately 5% more bone mass at the femoral neck (FN, measured by DXA) compared with same maturity control girls. However, only one study has evaluated the bone structural response to loading (by pQCT) in girls following a 9-month exercise trial.
To examine differences in bone structure and strength at the tibia between girls who completed a 20-month exercise intervention and controls.
We assessed bone structure and strength of the left tibia in 54 girls who participated in our Healthy Bones II Study (24 intervention (INT), 30 controls (CON). The 20-month intervention involved 10 minutes, 3x/week of loaded exercise performed during school physical education. We used pQCT (Norland XCT-2000) to measure trabecular area (cm2), trabecular density (mg/cm3), total bone area (cm2), and total density (mg/cm3) at the distal (10%) site. Cortical area (CA, cm2), cortical thickness (cm), periosteal and endosteal circumferences (cm) and cross sectional moment of inertia (cm4) were measured at the midshaft (50%). Height (ht) and weight (wt) were measured using standard procedures. Pubertal maturation was assessed using Tanner Staging (TS). General physical activity (PA) was assessed by questionnaire.
There was no difference between groups for age (12.2±0.5 yrs), ht (154.6±8.1 cm), wt (48.8±11.2 kg) or PA. CON girls were significantly more mature than INT girls (X2, P < 0.05). There was no difference between groups for bone strength or structural parameters (ANCOVA, ht, TS, PA and age as covariates). PA was significantly associated with CA (p < 0.05).
Despite significantly greater gains in FN BMC following a 20-month exercise intervention, there was no difference in bone structure or strength at the tibia between INT and CON girls. Although our results support the notion that bone response to loading is region and site specific, these conclusions are tempered by the nature of cross-sectional comparisons.