Impact Exercise Increases BMC During Growth: An 8-Year Longitudinal Study

Our aim was to assess BMC of the hip over 8 yr in prepubertal children who participated in a 7-mo jumping intervention compared with controls who participated in a stretching program of equal duration. We hypothesized that jumpers would gain more BMC than control subjects. The data reported come from two cohorts of children who participated in separate, but identical, randomized, controlled, school-based impact exercise interventions and reflect those subjects who agreed to long-term follow-up (N = 57; jumpers = 33, controls = 24; 47% of the original participants). BMC was assessed by DXA at baseline, 7 and 19 mo after intervention, and annually thereafter for 5 yr (eight visits over 8 yr). Multilevel random effects models were constructed and used to predict change in BMC from baseline at each measurement occasion. After 7 mo, those children that completed high-impact jumping exercises had 3.6% more BMC at the hip than control subjects whom completed nonimpact stretching activities (p \u3c 0.05) and 1.4% more BMC at the hip after nearly 8 yr (BMC adjusted for change in age, height, weight, and physical activity; p \u3c 0.05). This provides the first evidence of a sustained effect on total hip BMC from short-term high-impact exercise undertaken in early childhood. If the benefits are sustained into young adulthood, effectively increasing peak bone mass, fracture risk in the later years could be reduced

Lower limb stiffness and maximal sprint speed in 11-16-year-old boys

The purpose of the study was to examine the relationship between vertical stiffness, leg stiffness and maximal sprint speed in a large cohort of 11-16-year-old boys. Three-hundred and thirty-six boys undertook a 30 m sprint test using a floor-level optical measurement system, positioned in the final 15 m section. Measures of speed, step length, step frequency, contact time and flight time were directly measured whilst force, displacement, vertical stiffness and leg stiffness, were modeled from contact and flight times, from the two fastest consecutive steps for each participant over two trials. All force, displacement and stiffness variables were significantly correlated with maximal sprint speed (p 0.7) relationship with sprint speed, while vertical center of mass displacement, absolute vertical stiffness, relative peak force, and maximal leg spring displacement had large (r > 0.5) relationships. Relative vertical stiffness and relative peak force did not significantly change with advancing age (p > 0.05), but together with maximal leg spring displacement accounted for 96% of the variance in maximal speed. It appears that relative vertical stiffness and relative peak force are important determinants of sprint speed in boys aged 11-16 years, but are qualities that may need to be trained due to no apparent increases from natural development. Practitioners may wish to utilize training modalities such as plyometrics and resistance training to enable adaptation to these qualities due to their importance as predictors of speed in youth

Mineralogy of a Mudstone at Yellowknife Bay, Gale Crater, Mars

Sedimentary rocks at Yellowknife Bay (Gale Crater) on Mars include mudstone sampled by the Curiosity rover. The samples, John Klein and Cumberland, contain detrital basaltic minerals, Ca-sulfates, Fe oxide/hydroxides, Fe-sulfides, amorphous material, and trioctahedral smectites. The John Klein smectite has basal spacing of ~10 Å indicating little interlayer hydration. The Cumberland smectite has basal spacing at ~13.2 Å as well as ~10 Å. The ~13.2 Å spacing suggests a partially chloritized interlayer or interlayer Mg or Ca facilitating H_2O retention. Basaltic minerals in the mudstone are similar to those in nearby eolian deposits. However, the mudstone has far less Fe-forsterite, possibly lost with formation of smectite plus magnetite. Late Noachian/Early Hesperian or younger age indicates that clay mineral formation on Mars extended beyond Noachian time

Subcutaneous Fat Topography: Age Changes and Relationship to Cardiovascular Fitness in Canadians

We used principal components analysis of five skinfold measurements to determine 1) The statistical components of body fat topography in an adult population, 2) The relation of these to age and obesity levels and 3) The relationship of body fat topography to aerobic fitness in Canadians. Three components of fat topography were identified: a component of centralized fatness and another two of upper and lower body variations. All three increase with age in both men and women, that is, older Canadians have their fat more centrally located and more on the upper body than younger adults do. The component of centralized fatness is positively related to the body mass index (wt/stature2) in most all age/sex groups, and the centralized obese tend to have less overall subcutaneous fat than the gener­alized (peripheral) obese. These observations taken together suggest that this type of obesity may be due to enlarged intra-abdominal fat deposits. Reduced aerobic capacity is mainly dependent on fatness level measured as the mean of skinfold measurements. A centralized distribution of sub­cutaneous fat is also associated with decreased aerobic capacity in men, but not in women

Sensitivities, Specificities, and Positive Predictive Values ofSimple Indices of Body Fat Distribution

Centralized obesity has been associated with increased risk of non-insulin dependent diabetes and cardiovascular disease. Paramount to a sensitive index of body fat distribution is that it contain a measure of lower limb fat (Ashwell et al. 1978; 1982; Mueller and Stallones 1981). However, many epidemiological studies of body fat distribution, which have used skinfold measurements, have been limited to estimating centralized obesity from the triceps and subscapular or other conventional upper body sites. The purpose of this study was to evaluate the sensitivities, specificities, and positive predictive values of skinfold indices of body fat distribution when only sites on the upper body are available. We were able to do this in a large population-based data set, the Canadian YMCA-LIFE study, which in­cluded adults 25 to 64 years of age and skinfold sites from upper and lower anatomical regions of the body.Sensitivities, specificities, and positive predictive values did not vary systematically with age group, sex or obesity level. Sensitivities (mean = 70%) and positive predictive rates (mean = 65%) were moderate for the most common two site index (triceps/triceps + subscapular) and were not notably improved with the addition of the suprailiac site. Simple percent extremity fat indices (e.g. triceps/(triceps + subscapular) X 100) were as effective in discriminating body fat distribution groups as an index involving the same variables in the form of a vector of log transformed measurements. Substituting lower limb fat (medial calf) for arm fat (triceps) in simple percent indices, provided important additional information (mean sen­sitivity = 77%, mean positive predictive rate = 70%)

Physical activity and strength of the femoral neck during the adolescent growth spurt: A longitudinal analysis

Loading of the femoral neck (FN) is dominated by bending and compressive stresses. We hypothesize that adaptation of the FN to physical activity would be manifested in the cross-sectional area (CSA) and section modulus (Z) of bone, indices of axial and bending strength, respectively. We investigated the influence of physical activity on bone strength during adolescence using 7 years of longitudinal data from 109 boys and 121 girls from the Saskatchewan Paediatric Bone and Mineral Accrual Study (PBMAS). Physical activity data (PAC-Q physical activity inventory) and anthropometric measurements were taken every 6 months and DXA bone scans were measured annually (Hologic QDR2000, array mode). We applied hip structural analysis to derive strength and geometric indices of the femoral neck using DXA scans. To control for maturation, we determined a biological maturity age defined as years from age at peak height velocity (APHV). To account for the repeated measures within individual nature of longitudinal data, multilevel random effects regression analyses were used to analyze the data. When biological maturity age and body size (height and weight) were controlled, in both boys and girls, physical activity was a significant positive independent predictor of CSA and Z of the narrow region of the femoral neck (P < 0.05). There was no independent effect of physical activity on the subperiosteal width of the femoral neck. When leg length and leg lean mass were introduced into the random effects models to control for size and muscle mass of the leg (instead of height and weight), all significant effects of physical activity disappeared. Even among adolescents engaged in normal levels of physical activity, the statistically significant relationship between physical activity and indices of bone strength demonstrate that modifiable lifestyle factors like exercise play an important role in optimizing bone strength during the growing years. Physical activity differences were explained by the interdependence between activity and lean mass considerations. Physical activity is important for optimal development of bone strength. (c) 2005 Elsevier Inc. All rights reserved

Effect of maturational timing on bone mineral content accrual from childhood to adulthood: Evidence from 15 years of longitudinal data

A higher bone mass may reduce the risk of osteoporosis and fractures. The role of maturational timing for optimizing bone mass is controversial due to the lack of prospective evidence from childhood to adulthood. The purpose of this study was to examine the long term relationship between the onset of maturation and bone mineral content (BMC) development.Two hundred thirty individuals (109 males and 121 females) from the Saskatchewan Pediatric Bone Mineral Accrual Study (PBMAS) were classified into maturity groups based on age of peak height velocity. BMC was serially assessed using dual energy X-ray absorptiometry (DXA). Multilevel models were constructed to examine the independent development of BMC by maturity group.When age, body size, and body composition were controlled early maturing females had on average 3-4%, 62.2 ± 16.8. g (p 0.05) in females. There were no significant differences in BMC development at any site among male maturational groups (p > 0.05).In this group of healthy participants, there appears to be a sex-dependent effect on the relationship between maturational timing and total body BMC development. Early, average and late maturing males displayed similar BMC development. Late maturing females had compromised BMC accrual compared to their early and average maturing peers