Mechanical loading during childhood and adolescence may yield skeletal benefits that persist beyond activity cessation and menarche. At 1 year pre- and 2 years post-menarche, nondominant forearm areal bone mineral density (aBMD), bone mineral content (BMC) and projected area (area) were compared in gymnasts (n = 9), ex-gymnasts (n = 8) and nongymnasts (n = 13). At both observations, gymnasts and ex-gymnasts had higher forearm aBMD, BMC and area than nongymnasts. gymnasts had higher postmenarcheal means than ex-gymnasts for all three parameters. Childhood mechanical loading yields skeletal advantages that persist at least 24 months after loading cessation and menarche. Continued postmenarcheal loading yields additional benefit.
Tamara A. Scerpella, Jodi N. Dowthwaite, Nicole M. Gero, Jill A. Kanaley and Robert J. Ploutz-Snyder
Jill A. Kanaley, Richard A. Boileau, Benjamin H. Massey and James E. Misner
Changes in muscular efficiency as it relates to age were examined during inclined submaximal treadmill walking in 298 boys ages 7–15 years. Furthermore, the changes in efficiency with increased work intensity (67–90% V̇O2max) were studied. Efficiency was expressed as submaximal oxygen consumption (V̇O2) and was calculated mathematically as energy out/energy in = (vertical distance) (wt of subject)/(V̇O2 L • min−1) (kcal equivalent). Efficiency, calculated mathematically, was found to significantly increase (p<.01) with age, with the younger children (<9 yrs) being less efficient than the older children (13–15 yrs). These values ranged from 12.8% for the youngest boys (<9 yrs) to 16.4% for the oldest boys (13–15 yrs). In addition, efficiency significantly increased in a linear fashion (p<.01) during submaximal workloads within each age group. No significant interactions (p>.05) between age and workload were found. These values are lower than gross efficiency values during cycling previously reported in the literature for adults; however, they support earlier findings that children increase in efficiency with age and work intensity, regardless if expressed as efficiency or V̇O2 (ml • kg−1 •min−1). These findings suggest that parameters associated with growth and development may influence muscular efficiency with age.
Timothy D. Heden, Ying Liu, Young-Min Park, Nathan C. Winn and Jill A. Kanaley
This study assessed if walking at a self-selected pace could improve postprandial glucose and insulin concentrations in obese adolescents consuming high-fructose (HF) or high-glucose (HG) diets.
Seven obese male and female adolescents (18 ± 1 yr) performed 4, 15-day trials in a random order, including 1) HF-diet (50 g fructose/d added to normal diet) while being sedentary, 2) HG-diet (50 g glucose/d) while sedentary, 3) HF-diet with additional walking, and 4) HG-diet with additional walking. On the 15th day of each trial, the participants performed mixed meal testing in the laboratory in which they consumed three liquid shakes (either HF or HG) and during the HF and HG sedentary trials, the participants took < 4000 steps while in the laboratory but during the walking trials took ≥ 13,000 steps during testing.
Walking did not alter postprandial glucose concentrations. Although walking reduced insulin secretion by 34% and 25% during the HF- and HG-diet, respectively (P < .05), total insulin concentrations were only significantly reduced (P > .05) with walking during the HF trial, possibly because walking enhanced insulin clearance to a greater extent during the HF-diet.
Walking reduces postprandial insulin secretion in obese adolescents consuming a high-fructose or high-glucose diet.
Brittney Bernardoni, Tamara A. Scerpella, Paula F. Rosenbaum, Jill A. Kanaley, Lindsay N. Raab, Quefeng Li, Sijian Wang and Jodi N. Dowthwaite
We prospectively evaluated adolescent organized physical activity (PA) as a factor in adult female bone traits. Annual DXA scans accompanied semiannual records of anthropometry, maturity, and PA for 42 participants in this preliminary analysis (criteria: appropriately timed DXA scans at ~1 year premenarche [predictor] and ~5 years postmenarche [dependent variable]). Regression analysis evaluated total adolescent interscan PA and PA over 3 maturity subphases as predictors of young adult bone outcomes: 1) bone mineral content (BMC), geometry, and strength indices at nondominant distal radius and femoral neck; 2) subhead BMC; 3) lumbar spine BMC. Analyses accounted for baseline gynecological age (years pre- or postmenarche), baseline bone status, adult body size and interscan body size change. Gymnastics training was evaluated as a potentially independent predictor, but did not improve models for any outcomes (p < .07). Premenarcheal bone traits were strong predictors of most adult outcomes (semipartial r 2 = .21-0.59, p < .001). Adult 1/3 radius and subhead BMC were predicted by both total PA and PA 1-3 years postmenarche (p < .03). PA 3-5 years postmenarche predicted femoral narrow neck width, endosteal diameter, and buckling ratio (p < .05). Thus, participation in organized physical activity programs throughout middle and high school may reduce lifetime fracture risk in females.