This study involved a 28-week school-based exercise trial of single-leg drop-landing exercise with 42 girls (Tanner stage 1; 6-10 yr old) randomly assigned to control (C), low-drop (LD) or high-drop(HD) exercise groups. The latter two groups performed single-leg drop-landings (3 sessions.wk-1 and 50 landings.session-1) from 14cm and 28cm, respectively using the non-dominant leg. Single-leg peak ground-reaction impact forces (PGRIF) in a sub-sample ranged between 2.5 – 4.4 x body-weight (BW). No differences (p>0.05) among groups at baseline for age, stature, lean tissue mass (LTM - DXA - Lunar 3.6-DPX), leisure time physical activity or average daily calcium intake were detected. No significant within group changes for between leg differences from baseline to post-training and no significant differences among groups at baseline, or in magnitude of change for any of the dominant or non-dominant (loaded) leg bone mineral content (BMC g) measures determined by DXA – loaded leg total - 19.06, 25.5, 25.46 [p=.156], femoral neck - 0.14, 0.11, 0.15 [p=.959], greater trochanter - 0.37, 0.06, 0.26 [p=.733], mid femoral shaft - 3.87, 3.87, 3.42 [p=.677] for the C, LD and HD groups, respectively, after adjusting for the covariates baseline body and fat mass, and change in LTM (ANCOVA) were observed. Similarly, following ANCOVA adjustments no significant differences for changes in calcaneal speed of sound and broadband ultrasound attenuation (CUBA Clinical), DXA derived changes in femoral neck (-0.009, 0.033, -0.009; p=.189) and total MFS (0.029, 0.041, 0.053; p=.447) volumetric BMD (g.cm-3), or MFS cortical volumetric BMD, the latter derived by a new technique combining MRI and DXA were identified. TBBMC changed by 79.6g-C, 100.2g-LD and 91.9g-HD (p=.339). Combining data from both exercise groups to increase statistical power produced similar results. No significant within group changes for between leg differences from baseline to post-training and no significant differences among groups at baseline, or in magnitude of change for any of the dominant or non-dominant (loaded) leg bone geometrical (area cm2) determined by MRI using ANALYZE® software of proximal - 22.18, 12.91, 19.86 [p=.248], mid - 19.83, 15.91, 19.64 [p=.233], or distal - 14.78, 16.07, 13.35 [p=.792], slice cortical area for the C, LD and HD groups, respectively, after adjusting for the covariates baseline body and fat mass, and change in LTM (ANCOVA) were detected. Similarly there were no significant biomechanical cross sectional moment of inertia (CSMI cm4) changes determined by Scion Image® (Frederick, Maryland: Version-Beta 3B) and a custom macro program of proximal - 896, 815, 649 [p=.415], mid - 1054, 806, 1087 [p=.471], or distal - 1197, 1079, 966 [p=.606], slice CSMI for the C, LD and HD groups, respectively after adjusting for the same covariates. In contrast to some recent reports, our findings suggest that strictly controlled uni-modal; uni-directional single-leg drop-landing exercises involving low-moderate peak ground-reaction impact forces are not osteogenic in the developing prepubertal female skeleton.

Osteoporosis, a major public health problem, likely has its origins in childhood. During periods of rapid skeletal growth, diet may influence accrual of bone mineral density (BMD) and adult bone health. This study used novel approaches in bone imaging to further characterize optimal skeletal development and enhance our understanding of key dietary components that influence attainment of peak bone mass (PBM) and contribute to determinants of peak bone strength in peri-pubertal females. The use of a validated food-frequency questionnaire (FFQ) enabled the influence of usual dietary intake on bone parameters to be examined.This study examined the relationship of dietary intake of micronutrients and bone macro-architectural structure in peri-pubertal girls. This study suggested that vitamin C and zinc intake are associated with objective measures of bone status in 4th, but not 6th grade girls. This indicates potential differences in micronutrient and bone associations at various age-associated stages of bone maturation.The impact of dietary fat on peri-pubertal skeletal growth is not well characterized. This study examined relationships of select dietary fatty acid (FA) intakes and measures of bone status in peri-pubertal girls. This study suggested that MUFA, total PUFA, n-6 and linoleic acid (LA) are inversely associated with bone status prior to menarche, but composition of dietary fat may be more important during the early-pubertal years. Decreased intakes of n-6 PUFA may benefit bone health in young girls.The impact of a dietary protein on volumetric bone mineral density (vBMD), bone mineral content (BMC) and bone strength throughout maturation remains controversial. Given evidence of both anabolic and catabolic affects of protein on bone health, this study examined relations of dietary protein from different sources with bone parameters in peri-pubertal girls. This study showed that dietary protein intake is related to higher trabecular but not cortical vBMD, BMC and BSI, and accounts for 2-4% of their variability in peri-pubertal girls. The relationship seems to vary by the source of dietary protein and calcium intake. However, a negative impact of animal protein on bone health is not supported. Large scale observational and intervention studies are needed to establish causality.