Adjusted (±SE) changes in femur and tibia BSI (A) and SSIp (B) across groups of baseline thigh and calf muscle density. Differences among groups of baseline muscle density. were evaluated by ANCOVA using randomization, ethnicity, baseline measures of maturity offset, bone lengths, MCSA, 2-year change in maturity offset and average physical activity. MD=muscle density (mg/cm3); BSI=bone strength index (mg2/mm4); SSI=strength–strain index (mm3). aSignificantly different (P<0.03) from highest group; ANCOVA; bSignificantly (P<0.05) different from middle group; ANCOVA.