Patterns of physical performance spurts during adolescence: a cross-cultural study of Canadian, Brazilian and Portuguese boys.

BACKGROUND: Data relating physical performance to the timing of the adolescent growth spurt are limited. Aim: This study identifies: (i) age-at-peak height velocity (APHV), (ii) physical performance spurt patterns aligned to APHV; and (iii) cross-cultural and time patterns in Canadian, Brazilian and Portuguese boys. Subjects and methods: A total of 512 boys (131 Canadian, 250 Portuguese and 131 Brazilian), 8-17 years of age were followed serially using longitudinal data. APHV was identified and five physical performance measures velocities [trunk extension (TE), trunk flexion (TF), standing long jump (SLJ), curl-ups (CU) and handgrip strength (HG)] were aligned at 6-month intervals, 4 years around the attainment of PHV. Velocities were estimated using a non-smooth mathematical procedure. Results: APHV was 13.9 ± 1.0, 13.4 ± 1.6 and 13.0 ± 0.8 years for Canadian, Brazilian and Portuguese boys, respectively. Maximal velocity in SLJ was attained between 12 and 6 months prior to PHV. For HG, peaks were attained 12-24 months after PHV. Maximal velocity in TE occurred between 12 and 0 months prior to PHV, while CU peaked between PHV and 6 months after PHV. Conclusion: Patterns of spurts in physical performance have remained relatively the same and do not appear to be influenced by cross-cultural differences.

Jump starting skeletal health: a 4-year longitudinal study assessing the effects of jumping on skeletal development in pre and circum pubertal children.

INTRODUCTION: Evidence suggests bone mineral increases attributable to exercise training prior to puberty may confer a significant advantage into adulthood. However, there is a dearth of supportive prospective longitudinal data. The purpose of this study was to assess bone mineral content (BMC) of the whole body (WB), total hip (TH), femoral neck (FN) and lumbar spine (LS) over four years in pre-pubertal boys and girls following a 7-month jumping intervention. METHODS: The study population included 107 girls and 98 boys aged 8.6+/-0.88 years at baseline. Participating schools were randomly assigned as either intervention or control school. Children at the intervention school (n=101) participated in a jumping intervention embedded within the standard PE curriculum. The control school children (n=104) had similar exposure to PE without the jumping intervention. BMC was assessed by DXA at baseline, at 7-month post intervention, and annually thereafter for three years totaling 5 measurement opportunities. Multi-level random effects models were constructed and used to predict change from study entry in BMC parameters at each measurement occasion. RESULTS: A significant intervention effect was found at all bone sites. The effect was greatest immediately following the intervention (at 7 months) but still significant three years after the intervention. At 7 months, intervention participants had BMC values that were 7.9%, 8.4%, 7.7% and 7.3% greater than the controls at the LS, TH, FN and WB, respectively (p<0.05), when the confounders of age, maturity and tissue mass were controlled. Three years after the intervention had concluded the intervention group had 2.3%, 3.2%, 4.4% and 2.9% greater BMC than controls at the LS, TH, FN and WB respectively (p<0.05), when the confounders of age, maturity and tissue mass were controlled. CONCLUSIONS: This provides evidence that short-term high impact exercise in pre-puberty has a persistent effect over and above the effects of normal growth and development. If the benefits are sustained until BMC plateaus in early adulthood, this could have substantial effects on fracture risk.

The influence of physical activity on lean mass accrual during adolescence: a longitudinal analysis.

During childhood, physical activity is likely the most important modifiable factor for the development of lean mass. However, the effects of normal growth and maturation must be controlled. To distinguish effects of physical activity from normal growth, longitudinal data are required. One hundred nine boys and one hundred thirteen girls, participating in the Saskatchewan Pediatric Bone Mineral Accrual Study, were repeatedly assessed for 6 yr. Age at entry was 8-15 yr. Stature, body mass, and physical activity were assessed biannually. Body composition was assessed annually by dual-energy X-ray absorptiometry. Physical activity was determined using the physical activity questionnaires for children and adolescence. Biological age was defined as years from age of peak height velocity. Data were analyzed using multilevel random-effects models. In boys, it was found that physical activity had a significant time-dependent effect on lean mass accrual of the total body (484.7+/-157.1 g), arms (69.6+/-27.2 g), legs (197.7+/-60.5 g), and trunk (249.1+/-91.4 g) (P<0.05). Although the physical activity effects were similar in the girls (total body: 306.9+/-96.6 g, arms: 31.4+/-15.5 g, legs: 162.9+/-40.0 g, and trunk: 119.6+/-58.2 g; P<0.05), boys for the same level of activity accrued, depending on the site, between 21 and 120% more absolute lean mass (g). In conclusion, habitual physical activity had a significant independent influence on the growth of lean body mass during adolescence, once biological maturity and stature were controlled.

Growth and maturation of adolescent female gymnasts, swimmers, and tennis players.

UNLABELLED: Intensive training at a young age may adversely affect the growth and sexual maturation of female athletes, resulting in compromised adult stature. PURPOSE: To compare the somatic growth, sexual maturation, and final adult height of elite adolescent female athletes. METHODS: Serial measures of height, sitting height, and breast and pubic hair development were taken on 81 gymnasts, 60 swimmers, and 81 tennis players between 8 and 19 yr of age. Menarcheal age, parental heights, maternal menarcheal age, and number of training hours were also recorded. Final adult heights were obtained from a subsample of the athletes (N = 110). RESULTS: Gymnasts were significantly shorter than tennis players and swimmers at all chronological ages during adolescence, and they attained menarche at an older age (P < 0.05). No significant differences were found in adult heights. During adolescence, no difference were found in standing height to sitting height ratios, leg length to standing height ratios, or sitting height to leg length ratios between sports (P > 0.05). CONCLUSION: The results from this study suggest that regular training did not affect final adult stature and that, when aligned by biological age, the tempo of sexual maturation was similar in these young athletes.

Size-corrected BMD decreases during peak linear growth: implications for fracture incidence during adolescence.

UNLABELLED: Peak adolescent fracture incidence at the distal end of the radius coincides with a decline in size-corrected BMD in both boys and girls. Peak gains in bone area preceded peak gains in BMC in a longitudinal sample of boys and girls, supporting the theory that the dissociation between skeletal expansion and skeletal mineralization results in a period of relative bone weakness. INTRODUCTION: The high incidence of fracture in adolescence may be related to a period of relative skeletal fragility resulting from dissociation between bone expansion and bone mineralization during the growing years. The aim of this study was to examine the relationship between changes in size-corrected BMD (BMDsc) and peak distal radius fracture incidence in boys and girls. MATERIALS AND METHODS: Subjects were 41 boys and 46 girls measured annually (DXA; Hologic 2000) over the adolescent growth period and again in young adulthood. Ages of peak height velocity (PHV), peak BMC velocity (PBMCV), and peak bone area (BA) velocity (PBAV) were determined for each child. To control for maturational differences, subjects were aligned on PHV. BMDsc was calculated by first regressing the natural logarithms of BMC and BA. The power coefficient (pc) values from this analysis were used as follows: BMDsc = BMC/BA(pc). RESULTS: BMDsc decreased significantly before the age of PHV and then increased until 4 years after PHV. The peak rates in radial fractures (reported from previous work) in both boys and girls coincided with the age of negative velocity in BMDsc; the age of peak BA velocity (PBAV) preceded the age of peak BMC velocity (PBMCV) by 0.5 years in both boys and girls. CONCLUSIONS: There is a clear dissociation between PBMCV and PBAV in boys and girls. BMDsc declines before age of PHV before rebounding after PHV. The timing of these events coincides directly with reported fracture rates of the distal end of the radius. Thus, the results support the theory that there is a period of relative skeletal weakness during the adolescent growth period caused, in part, by a draw on cortical bone to meet the mineral demands of the expanding skeleton resulting in a temporary increased fracture risk.

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.

Relationships of activity and sugar drink intake on fat mass development in youths.

PURPOSE: To determine whether a significant relationship exists between fat mass (FM) development and physical activity (PA) and/or sugar-sweetened drink (SD) consumption in healthy boys and girls aged 8-19 yr. METHODS: A total of 105 males and 103 females were assessed during childhood and adolescence for a maximum of 7 yr and a median of 5 yr. Height was measured biannually. Fat-free mass (FFM) and FM were assessed annually by dual x-ray absorptiometry (DXA). PA was evaluated two to three times annually using the PAQ-C/A. Energy intake and SD were assessed using a 24-h dietary intake questionnaire also completed two to three times per year. Years from peak height velocity were used as a biological maturity age indicator. Multilevel random effects models were used to test the relationship. RESULTS: When controlling for maturation, FFM, and energy intake adjusted for SD, PA level was negatively related to FM development in males (P<0.05) but not in females (P>0.05). In contrast, there was no relationship between SD and FM development of males or females (P>0.05). There was also no interaction effect between SD and PA (P>0.05) with FM development. CONCLUSION: This finding lends support to the idea that increasing PA in male youths aids in the control of FM development. Models employed showed no relationship between SD and FM in either gender.

Evidence of sustained skeletal benefits from impact-loading exercise in young females: a 3-year longitudinal study.

UNLABELLED: The skeletal effects from intensive exercise throughout puberty are undefined. Forty-five female gymnasts and 52 controls were studied over 3 years, including a heredity aspect. The effects of size, maturity, exercise, and diet were identified using a multilevel regression model. Results demonstrated sustained skeletal benefits resulting from exercise throughout all stages of pubertal development. INTRODUCTION: Weight-bearing exercise is beneficial for peak bone mass development. However, whether skeletal benefits achieved with exercise are maintained if training remains intensive throughout the pubertal years is not entirely clear. The influence of familial resemblance for bone mass remains undefined in physically active versus inactive children. The aim of this study was to investigate the long-term influences of impact-loading exercise on bone quantity and quality in young females after controlling for growth, maturation, and hereditary factors. MATERIALS AND METHODS: At baseline, 45 gymnasts (G) and 52 normally active controls (C) 8-17 years of age were recruited. Anthropometry, diet, physical activity, and quantitative ultrasound (QUS) were measured annually for 3 consecutive years. DXA scans of total body (TB) and lumbar spine (LS) bone mineral content (BMC) and density (BMD) were taken three times at 1-year intervals. A multilevel regression model was fitted, and the independent effects of body size, maturity, physical activity, and diet were identified over time. To assess heredity influences, 27 G mothers and 26 C mothers volunteered for cross-sectional measurements of anthropometry, QUS, and BMC/BMD. RESULTS AND CONCLUSIONS: Gymnasts were smaller and lighter (as were their mothers) than controls, but they had significantly higher QUS and axial and appendicular BMC and BMD, with > 170 g more bone mineral in TB across puberty (after adjustment for maturity [years from peak height velocity], height, weight, energy, and protein intake). Gymnasts had up to 24-51% higher BMC and 13-28% higher BMD, depending on skeletal site. These results provide evidence of sustained skeletal benefits from impact-loading exercise, which are unlikely to result entirely from heredity, throughout pubertal years.

Sexual dimorphism of the femoral neck during the adolescent growth spurt: a structural analysis.

Before puberty, there are only small sex differences in body shape and composition. During adolescence, sexual dimorphism in bone, lean, and fat mass increases, giving rise to the greater size and strength of the male skeleton. The question remains as to whether there are sex differences in bone strength or simply differences in anthropometric dimensions. To test this, we applied hip structural analysis (HSA) to derive strength and geometric indices of the femoral neck using bone densitometry scans (DXA) from a 6-year longitudinal study in Canadian children. Seventy boys and sixty-eight girls were assessed annually for 6 consecutive years. At the femoral neck, cross-sectional area (CSA, an index of axial strength), subperiosteal width (SPW), and section modulus (Z, an index of bending strength) were determined, and data were analyzed using a hierarchical (random effects) modeling approach. Biological age (BA) was defined as years from age at peak height velocity (PHV). When BA, stature, and total-body lean mass (TB lean) were controlled, boys had significantly higher Z than girls at all maturity levels (P < 0.05). Controlling height and TB lean for CSA demonstrated a significant independent sex by BA interaction effect (P < 0.05). That is, CSA was greater in boys before PHV but higher in girls after PHV. The coefficients contributing the greatest proportion to the prediction of CSA, SPW, and Z were height and lean mass. Because the significant sex difference in Z was relatively small and close to the error of measurement, we questioned its biological significance. The sex difference in bending strength was therefore explained by anthropometric differences. In contrast to recent hypotheses, we conclude that the CSA-lean ratio does not imply altered mechanosensitivity in girls because bending dominates loading at the neck, and the Z -lean ratio remained similar between the sexes throughout adolescence. That is, despite the greater CSA in girls, the bone is strategically placed to resist bending; hence, the bones of girls and boys adapt to mechanical challenges in a similar way.

Comparison of physical activity in male and female children: does maturation matter?

PURPOSE: To investigate whether observed differences in physical activity levels in boys and girls are confounded by biological age differences particularly during the circumpubertal years. METHODS: The physical activity questionnaire for children (PAQ-C) was administered biannually or triannually to 138 (70 boys; 68 girls) Canadian children for seven consecutive years from 1991 to 1997. Participants were 9-18 yr of age. Anthropometric measurements were taken biannually and age at peak height velocity (PHV) determined. Biological age was defined as years from PHV. The data were analyzed using t-tests and random effects models. RESULTS: Level of physical activity decreased with increasing chronological age in both sexes. When aligned on chronological age bands, boys had statistically significantly higher PAQ-C summary scores than girls from 10 through 16 yr of age (P < 0.05). However, when aligned on biological age, sex differences were not apparent, except at 3 yr before PHV. Random effects models of individual growth patterns confirmed these findings. CONCLUSION: Physical activity decreased with increasing chronological age in boys and girls. There were no sex differences in the longitudinal pattern of physical activity when the confounding effects of biological age were controlled except at 3 yr before PHV.

An assessment of maturity from anthropometric measurements.

PURPOSE: The range of variability between individuals of the same chronological age (CA) in somatic and biological maturity is large and especially accentuated around the adolescent growth spurt. Maturity assessment is an important consideration when dealing with adolescents, from both a research perspective and youth sports stratification. A noninvasive, practical method predicting years from peak height velocity (a maturity offset value) by using anthropometric variables is developed in one sample and cross-validated in two different samples. METHODS: Gender specific multiple regression equations were calculated on a sample of 152 Canadian children aged 8-16 yr (79 boys; 73 girls) who were followed through adolescence from 1991 to 1997. The equations included three somatic dimensions (height, sitting height, and leg length), CA, and their interactions. The equations were cross-validated on a combined sample of Canadian (71 boys, 40 girls measured from 1964 through 1973) and Flemish children (50 boys, 48 girls measured from 1985 through 1999). RESULTS: The coefficient of determination (R2) for the boys' model was 0.92 and for the girls' model 0.91; the SEEs were 0.49 and 0.50, respectively. Mean difference between actual and predicted maturity offset for the verification samples was 0.24 (SD 0.65) yr in boys and 0.001 (SD 0.68) yr in girls. CONCLUSION: Although the cross-validation meets statistical standards for acceptance, caution is warranted with regard to implementation. It is recommended that maturity offset be considered as a categorical rather than a continuous assessment. Nevertheless, the equations presented are a reliable, noninvasive and a practical solution for the measure of biological maturity for matching adolescent athletes

Intraindividual allometric development of aerobic power in 8- to 16-year-old boys.

PURPOSE: The aims of this study are two-fold: first, to analyze intraindividual allometric development of aerobic power of 73 boys followed at annual intervals from 8 to 16 yr, and second, to relate scaled aerobic power with level of habitual physical activity and biological maturity status. METHODS: Peak VO2 (treadmill), height, and body mass were measured. Biological maturity was based on age at peak height velocity (PHV) and level of physical activity was based on five assessments between 11 and 15 yr and at 17 yr. Interindividual and intraindividual allometric coefficients were calculated. Multilevel modeling was applied to verify if maturity status and activity explain a significant proportion of peak VO2 after controlling for other explanatory characteristics. RESULTS: At most age levels, interindividual allometry coefficients for body mass exceed k = 0.750. Intraindividual coefficients of peak VO2 by body mass vary widely and range from k' = 0.555 to k' = 1.178. Late maturing boys have smaller k' coefficients than early maturing boys. CONCLUSION: Peak VO2 is largely explained by body mass, but activity level and its interaction with maturity status contribute independently to peak VO2 even after adjusting for body mass.

A longitudinal study of the impact of childhood and adolescent physical activity experiences on adult physical activity perceptions and behaviors.

The authors describe the influence of childhood and adolescent physical activity on adult physical activity attitudes and behaviors. They conducted one-on-one, semistructured, indepth interviews with 16 men and 15 women from a longitudinal growth and development study and a follow-up investigation 25 years later. They used thematic analyses to analyze the data. Three themes emerged from the men's interviews: significant others, size and maturation, and physical ability, with clear distinctions among the active, average, and inactive men. The themes transitions, body image concerns, and significant others influenced the active, average, and inactive women. Specific relationships, circumstances, and attitudes formed in childhood and adolescence influenced adult physical activity predilection and behaviors.

Bone mineral accrual from 8 to 30 years of age: an estimation of peak bone mass.

Bone area (BA) and bone mineral content (BMC) were measured from childhood to young adulthood at the total body (TB), lumbar spine (LS), total hip (TH), and femoral neck (FN). BA and BMC values were expressed as a percentage of young-adult values to determine if and when values reached a plateau. Data were aligned on biological ages [years from peak height velocity (PHV)] to control for maturity. TB BA increased significantly from -4 to +4 years from PHV, with TB BMC reaching a plateau, on average, 2 years later at +6 years from PHV (equates to 18 and 20 years of age in girls and boys, respectively). LS BA increased significantly from -4 years from PHV to +3 years from PHV, whereas LS BMC increased until +4 from PHV. FN BA increased between -4 and +1 years from PHV, with FN BMC reaching a plateau, on average, 1 year later at +2 years from PHV. In the circumpubertal years (-2 to +2 years from PHV): 39% of the young-adult BMC was accrued at the TB in both males and females; 43% and 46% was accrued in males and females at the LS and TH, respectively; 33% (males and females) was accrued at the FN. In summary, we provide strong evidence that BA plateaus 1 to 2 years earlier than BMC. Depending on the skeletal site, peak bone mass occurs by the end of the second or early in the third decade of life. The data substantiate the importance of the circumpubertal years for accruing bone mineral.

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 ± 16.8g (p<0.05), more total body BMC than their average maturing peers by 20 years of age. In contrast, late maturing females had 50.7 ± 15.6g less total body BMC. No maturational effects were found at either the lumbar spine or femoral neck (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.

International longitudinal pediatric reference standards for bone mineral content.

To render a diagnosis pediatricians rely upon reference standards for bone mineral density or bone mineral content, which are based on cross-sectional data from a relatively small sample of children. These standards are unable to adequately represent growth in a diverse pediatric population. Thus, the goal of this study was to develop sex and site-specific standards for BMC using longitudinal data collected from four international sites in Canada and the United States. Data from four studies were combined; Saskatchewan Paediatric Bone Mineral Accrual Study (n=251), UBC Healthy Bones Study (n=382); Penn State Young Women's Health Study (n=112) and Stanford's Bone Mineral Accretion study (n=423). Males and females (8 to 25 years) were measured for whole body (WB), total proximal femur (PF), femoral neck (FN) and lumbar spine (LS) BMC (g). Data were analyzed using random effects models. Bland-Altman was used to investigate agreement between predicted and actual data. Age, height, weight and ethnicity independently predicted BMC accrual across sites (P<0.05). Compared to White males, Asian males had 31.8 (6.8) g less WB BMC accrual; Hispanic 75.4 (28.2) g less BMC accrual; Blacks 82.8 (26.3) g more BMC accrual with confounders of age, height and weight controlled. We report similar findings for the PF and FN. Models for females for all sites were similar with age, height and weight as independent significant predictors of BMC accrual (P<0.05). We provide a tool to calculate a child's BMC Z-score, accounting for age, size, sex and ethnicity. In conclusion, when interpreting BMC in pediatrics we recommend standards that are sex, age, size and ethnic specific.

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 < 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 < 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.

The influence of dance training on growth and maturation of young females: a mixed longitudinal study.

BACKGROUND: The effects of systematic sports training during childhood and adolescence on subsequent growth and sexual maturation remains in dispute. AIM: The study aimed to determine whether moderate-high volumes of dance training adversely influence linear growth and sexual maturation of young girls progressing through puberty. SUBJECTS AND METHODS: This 3-year mixed longitudinal study comprised 82 novice dancers and 61 controls, aged 8-11 years at baseline, who were assessed bi-annually for 3 consecutive years. A biological maturational age was determined by estimating attainment of age at peak height velocity (PHV). Body dimensions were measured by anthropometry, and exercise levels, nutritional intake and age at menarche by questionnaires. RESULTS: Controls had significantly greater unadjusted height velocity than dancers 1 year before PHV, however there was no difference between groups in age of attainment of PHV. When controlling for maturation, lean mass, fat mass and extracurricular sport (excluding dancing), there were no group differences in absolute growth or velocity of growth in height, sitting height or leg length. Within the dancers there were no effects of years of dancing (>6.5 years) or weekly dance hours (>7 h per week) on growth velocities. No association was found between age at menarche and years or hours of dance training. CONCLUSION: Results suggest that moderate-high levels of dance training do not affect linear growth and maturation. Thus, girls should not be discouraged from dance participation on the basis of potential growth delays.

Prediction of adult height using maturity-based cumulative height velocity curves.

OBJECTIVE: To validate and demonstrate how adult height can be predicted by using reference values obtained from maturity and sex-specific cumulative height velocity curves. STUDY DESIGN: Serial height measurements were taken on 224 boys and 120 girls. Individuals were classified as early, average, or late maturers, depending on their age of peak height velocity. Maturity and sex-specific cumulative height velocity curves were developed for early, average, and late maturers, and the area under these curves were used to develop reference values to predict adult height. RESULTS: This method can predict adult height within +/-5.35 cm 95% of the time in boys and +/-6.81 cm 95% of the time in girls. CONCLUSIONS: The technique is a valid, nonintrusive, inexpensive, and simple method of predicting adult height in adolescent children, free of growth limiting diseases.

Dietary protein, phosphorus and potassium are beneficial to bone mineral density in adult men consuming adequate dietary calcium.

OBJECTIVE: The purpose of this study was to determine relationships of calcium (Ca), protein (Pr), phosphorus (P) and potassium (K) to measures of bone mineral density in adult men. METHODS: Cross-sectional analysis of 57 men ages 39 to 42 years who were participants in an ongoing study. Dietary assessment was conducted using the Block food frequency questionnaire (FFQ). BMD of total body (TB), hip and lumbar spine (LS) were measured with dual X-ray absorptiometry (DXA). RESULTS: Ca, Pr, P and K, as well as lean body mass (LBM), showed significant correlation with BMD at the total body, hip and lumbar spine. Stepwise forward regression selection method identified LBM, height and fat mass as significant predictors of TB-BMD, LBM and height as significant predictors of hip BMD, and LBM as a significant predictor of LS-BMD. As the nutrients tested correlated significantly with each other, only one nutrient was entered into the regression model at a time to accommodate the potential for multicollinearity. In regression analysis, adjusted for site-specific anthropometric variables and energy intake, K, Pr and P intake accounted for significant (p < 0.05) prediction of TB-BMD and LS-BMD values by 7% to 13%. No bone-related nutrient added significantly to the prediction of hip BMD. Ca intake was not significantly associated with BMD at any site in the adjusted models. CONCLUSIONS: Our analysis provides support that a moderate protein (1.2 g/kg) diet, plentiful in potassium (>100 mmol/day) and phosphorus (1741 +/- 535 mg) is beneficial for maintaining bone mineral density in adult men when Ca intake was adequate (1200 +/- 515 mg).