1079 Exercise associated muscle induced bone strain has potential osteogenic effects that may increase skeletal density, bone cross-sectional area and structural strength. Whether the effects of exercise and the muscle-bone relation are similar in weight bearing and non-weight bearing bones remains to be determined. PURPOSE: This study compared bone density, as well as bone and muscle cross-sectional areas of 13 adolescent male cross-country skiers competing at the Provincial and National levels with published age and maturity matched normative data (ND) on healthy non-athletic males. METHODS: Skiers were 17.3 +/− 1.1 years old, 177.4 +/−4.4 cm tall, 70.2 +/− 8.25 kg, 12.4+/−4.3% body fat, and Tanner Stage 4.8 +/−0.6. Total bone mineral content (BMCTOT), and total (BMDTOT) bone mineral density, cortical thickness and area (CSAcort), muscle cross-sectional area (mCSA) and the CSAcort/mCSA ratio were measured at the 66 % length of the proximal tibia (PT) using peripheral quantitative computed tomography (pQCT 2000, Stratec, Pforzheim, Germany). BMCTOT, CSAcort TOT and mCSA were also measured at the proximal radius (PR-66% length). RESULTS: PR BMCTOT of the skiers was not significantly different (98.99 +/− 18.87mg/mm) than controls (94 +/− 20mg/mm). Likewise, PT CSAcort, mCSA, as well as the CSAcort/mCSA ratios were similar between skiers and controls. Cortical thickness and BMDTOT at the PT were significantly higher in skiers (5.423+/−0.254mm p = 0.000; 649.3 +/− 65.6mg/cm3 p = 0.0064) than controls (3.909+/−0.467mm; 574.1+/−56.5mg/cm3). A difference was seen in the CSAcort/mCSA ratio between PR (0.022 +/− 0.004) and PT (0.048 +/− 0.005) suggesting differences in muscle-bone relations between load bearing and non-load bearing limbs in adolescent male cross-country skiers. CONCLUSION: Cross-country skiers had increased cortical thickness and BMDTOT at the PT compared to ND and a higher cortical bone/muscle area ratio at the PT compared to the PR, suggesting regional variability in the muscle-bone relation. Supported in part by Stratec, Pforzheim, Germany.