A COMPARATIVE MAGNETIC RESONANCE IMAGING STUDY OF THE LOWER LIMB IN PREPUBERTAL FEMALE GYMNASTS

Abstract

1606 The effects of chronic, intense physical training on the musculoskeletal system were investigated in prepubescent females. 10 competitive (TG; mean age 9.5 ± 1.2 yrs) and 8 recreational (RG; mean age 9.2 ± 1.1 yrs) gymnasts participated in this study. Maturation status was determined by self-assessed Tanner stages and pre-menarche. Magnetic resonance imaging was employed using a 3.0 T NMR system to measure gastrocnemius muscle cross sectional area (GCSA) and tibial cross sectional area (TCSA) in the right leg. Five 5mm slices were imaged around the point of maximal calf girth to find the largest GCSA. Combined medial and lateral gastrocnemius are reported as whole muscle GCSA. TCSA was measured from the same image as GCSA. Subjects also completed a supramaximal bout of exercise involving 2 min of dynamic work at 140% of their predetermined maximal unilateral plantar flexion work capacity. The groups did not differ in stature, body mass, absolute GCSA or TCSA. However, when GCSA was corrected for body mass, TG values were greater (p<.05) than RG. Similar results were observed when TCSA was corrected for body size (p<.05). When exercise work loads were expressed relative to GCSA, the TG values were higher than those of RG (p<.05). These results demonstrate the significant influence of physical training on both muscle and bone development in prepubertal females. While the training was not controlled in this cross sectional study, an extensive training and competition history clearly distiguished the TG from the RG. The larger TCSA in the TG provides evidence for training induced osteogenic activity. Further, the higher work outputs per GCSA in the TG suggest greater neuromuscular control compared to the less well trained RG. Supported by the Sport Science Association of Alberta