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.

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.

Relationship between trajectories of trunk fat mass development in adolescence and cardiometabolic risk in young adulthood.

To examine developmental trajectories of trunk fat mass (FM) growth of individuals categorized as either low or high for cardiometabolic risk at 26 years, a total of 55 males and 76 females from the Saskatchewan Pediatric Bone Mineral Accrual Study (1991-2007) were assessed from adolescence (11.5 ± 1.8 years) to young adulthood (26.2 ± 2.2 years) (median of 11 visits per individual) and had a measure of cardiometabolic risk in young adulthood. Participants were categorized as low or high for blood pressure and cardiometabolic risk as adults using a sex-specific median split of continuous standardized risk scores. Individual trunk FM trajectories of participants in each risk group were analyzed using multilevel random effects models. Males and females in the high blood pressure group had significantly steeper (accelerated) trajectories of trunk FM development (0.61 ± 0.14 and 0.52 ± 0.10 log g, respectively) than those in the low blood pressure group for females in the high cardiometabolic risk group trajectory of trunk FM was significantly steeper (0.52 ± 0.10 log g) than those females in the low cardiometabolic risk group. Dietary fat was positively related (0.01 ± 0.003 g/1,000 kcal) and physical activity negatively related (-0.16 ± 0.05 physical activity score) to trunk FM development in males. Young adults with high cardiometabolic risk, compared to low, have greater trunk FM as early as 8 years of age, which supports the need for early intervention.

Does controlling for biological maturity improve physical activity tracking?

UNLABELLED: Tracking of physical activity through childhood and adolescence tends to be low. Variation in the timing of biological maturation within youth of the same chronological age (CA) might affect participation in physical activity and may partially explain the low tracking. PURPOSE: To examine the stability of physical activity over time from childhood to late adolescence when aligned on CA and biological age (BA). METHODS: A total of 91 males and 96 females aged 8-15 yr from the Saskatchewan Pediatric Bone Mineral Accrual Study (PBMAS) were assessed annually for 8 yr. BA was calculated as years from age at peak height velocity. Physical activity was assessed using the Physical Activity Questionnaire for Children/Adolescents. Tracking was analyzed using intraclass correlations for both CA and BA (2-yr groupings). To be included in the analysis, an individual required a measure at both time points within an interval; however, not all individuals were present at all tracking intervals. RESULTS: Physical activity tracking by CA 2-yr intervals were, in general, moderate in males (r=0.42-0.59) and females (r=0.43-0.44). However, the 9- to 11-yr CA interval was low and nonsignificant (r=0.23-0.30). Likewise, tracking of physical activity by BA 2-yr intervals was moderate to high in males (r=0.44-0.60) and females (r=0.39-0.62). CONCLUSIONS: Accounting for differences in the timing of biological maturity had little effect on tracking physical activity. However, point estimates for tracking are higher in early adolescence in males and to a greater extent in females when aligned by BA versus CA. This suggests that maturity may be more important in physical activity participation in females than males.

Does childhood and adolescence fracture influence bone mineral content in young adulthood?

Previous fracture may predispose an individual to bone fragility because of impaired bone mineral accrual. The primary objective of the study was to investigate the influence of fractures sustained during childhood and (or) adolescence on total body (TB), lumbar spine (LS), femoral neck (FN), and total hip (TH) bone mineral content (BMC) in young adulthood. It was hypothesized that there would be lower TB, LS, FN, and TH BMC in participants who had sustained a pediatric fracture. Participant anthropometrics, physical activity, and BMC (measured with dual energy X-ray absorptiometry) were assessed longitudinally during childhood and adolescence (from 1991 to 1997), and again in young adulthood (2002 to 2006). Sex, adult height, adult lean mass, adult physical activity, and adolescent BMC adjusted TB, LS, FN, and TH BMC in young adulthood, for those who reported 1 or more fractures (n = 42), were compared with those who reported no fractures (n = 101). There were no significant differences (p > 0.05) in adjusted BMC between fracture and nonfracture groups at the TB, LS, FN, and TH sites in young adulthood. These results suggest that fractures sustained during childhood and adolescence may not interfere with bone mass in young adulthood at clinically relevant bone sites.

Calcium requirements for bone growth in Canadian boys and girls during adolescence.

Adequate dietary intake during the growth period is critical for bone mineral accretion. In 1997, an adequate intake (AI) of 1300 mg/d Ca was set for North American adolescents aged 9-18 years based on best available data. We determined bone Ca accrual values from age 9 to 18 years taking into account sex and maturity. Furthermore, we used the accrual data to estimate adolescents' Ca requirements. Total body bone mineral content (TBBMC) of eighty-five boys and sixty-seven girls participating in the Saskatchewan Paediatric Bone Mineral Accrual Study were used to determine annual TBBMC accumulation over the pubertal growth period. Using a similar factorial approach as the AI, we estimated Ca requirements of adolescent boys and girls for two age groups: 9-13 and 14-18 years. Between 9 and 18 years, boys accrued 198.8 (SD 74.5) g bone mineral content (BMC) per year, equivalent to 175.4 (SD 65.7) mg Ca per d with the maximum BMC accrual of 335.9 g from age 13 to 14 years. Girls had 138.1 (SD 64.2) g BMC per year, equalling121.8 (SD 56.6) mg Ca per d with the maximum annual BMC accrual of 266.0 g from age 12 to 13 years. Differences were observed between both sex and age groups with respect to Ca needs: boys and girls aged 9-13 years would require 1000-1100 mg/d Ca, and from age 14 to 18 years, the mean Ca requirements would be relatively stable at 1000 mg/d for girls but would rise to 1200 mg/d for boys.

A longitudinal study of the relationship of physical activity to bone mineral accrual from adolescence to young adulthood.

Physical activity in adolescence is beneficial for increasing bone mineral accrual; however, it's unclear whether these benefits persist into adulthood. This prospective study investigated whether physically active adolescents maintained their higher bone mineral content (BMC) into the third decade of life when compared to their less active peers. Data were from 154 subjects (82 females and 72 males) who participated in the University of Saskatchewan's Pediatric Bone Mineral Accrual Study (1991-1997), entry age 8 to 15 years. Participants returned for follow-up as young adults (2002-2006), follow-up age 23 to 30 years. Dual energy X-ray absorptiometry was used to measure BMC of total body (TB), lumbar spine (LS), total hip (TH) and femoral neck (FN) annually from 1991 to 1997 and from 2002 to 2006. Peak height velocity (PHV) was determined for each child as a measure of maturity. Age and gender-specific activity Z-scores were calculated for each participant based on the mean physical activity scores obtained from bi-annual questionnaire data during childhood and adolescence. Subjects were ranked into three adolescent activity groups: active, average and inactive (top, middle two, and bottom quartiles, respectively). Analysis of covariance (ANCOVA) was used to compare adjusted TB, LS, TH and FN BMC across the three adolescent activity groups at 1 year post PHV and in young adulthood. When compared to the inactive group, active males had 8% greater adjusted BMC at the TB, 13% at the LS and 11% at the TH (p<0.05) in adolescence. Active females also had 8% and 15% more adjusted BMC (p<0.05) at the TB and LS, respectively, during adolescence. In young adulthood the male and female adolescent active groups were still significantly more active than their peers (p>0.05). It was found that active adolescent males had 8-10% more adjusted BMC at the TB, TH and FN (p<0.05) in young adulthood and that active adolescent females had 9% and 10% more adjusted BMC at the TH and FN. These results suggest that the skeletal benefits of physically activity in adolescents are maintained into young adulthood.

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.

The effects of dietary protein on bone mineral mass in young adults may be modulated by adolescent calcium intake.

The effect of dietary protein on bone mass measures at different life stages is controversial. We investigated the influence of protein intake on bone mass measures in young adults, considering the influence of calcium intake through adolescence. Subjects were 133 young adults (59 males, 74 females) who were participating in the Saskatchewan Pediatric Bone Mineral Accrual Study (1991-1997, 2003-2006). At adulthood, their mean age was 23 y. We assessed dietary intake via serial 24-h recalls carried out at least once yearly. Total body (TB) bone mineral content (BMC) and TB bone mineral density (BMD) were assessed annually using Dual energy X-ray absorptiometry. We determined TB-BMC net gain from the age of peak height velocity (PHV) to early adulthood. We analyzed data from all subjects and subsets based on sex and calcium intake using multiple regression. TB-BMC significantly increased from age at PHV to early adulthood by 41% in males and 37% in females. Height, weight, physical activity, and sex were significant predictors of TB-BMC, TB-BMC net gain, and TB-BMD among all subjects. Protein intake predicted TB-BMC net gain in all subjects (beta = 0.11; P = 0.015). In females at peri-adolescence or early adulthood with adequate calcium intake (>1000 mg/d), protein intake positively predicted TB-BMC, TB-BMC net gain, and TB-BMD (P < 0.05). Our results indicate that when calcium intake is adequate, protein intake has a beneficial effect on the bone mass of young adult females. Protein, in the absence of sufficient calcium, does not confer as much benefit to bone.

Osteoporosis: a pediatric concern?

Osteoporosis and related fractures are a major public health concern globally, and the incidence and subsequent morbidity, mortality and health care costs are expected to increase dramatically over the coming decades. Although osteoporosis was once considered (primarily) a disease of the elderly, there is now universal agreement that the condition has pediatric antecedents. Although genetic factors play an important role in the attainment of an optimal adult (peak) bone mass and strength, lifestyle factors such as physical activity and nutrition are also important determinants of children's bone development. However, there is still much research needed to identify the exact role of modifiable lifestyle factors and childhood illness on long-term adult bone health and fracture risk. Much of our current knowledge is based on bone mineral content and areal bone mineral density assessed by dual-energy X-ray absorptiometry; but with rapidly advancing technology, researchers will be able to more accurately assess other indices of bone strength, such as the material and structural properties of bone, during the growing years. Based on our current knowledge, however, it is clear that intervention strategies aimed at reducing the incidence of osteoporosis must begin in childhood or adolescence if they are to have maximal effect.

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.

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.

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.

Positive effects of vegetable and fruit consumption and calcium intake on bone mineral accrual in boys during growth from childhood to adolescence: the University of Saskatchewan Pediatric Bone Mineral Accrual Study.

BACKGROUND: Nutrition is an important modifiable factor in the development of bone mass during adolescence. Recent studies of children and adolescents examined the effects of foods such as milk products and fruit and vegetables on bone growth; however, few studies included both boys and girls. OBJECTIVE: The purpose was to ascertain the role of consumption of milk products and vegetables and fruit in the accrual of total-body bone mineral content (TBBMC) in boys and girls from childhood to late adolescence. DESIGN: Seven-year longitudinal data were obtained from 85 boys and 67 girls aged 8-20 y. Biological maturity was defined by the number of years from the age at peak height velocity. Dietary intake was assessed by serial 24-h recalls. Anthropometric measurements and physical activity were assessed every 6 mo. TBBMC assessed with dual-energy X-ray absorptiometry in the fall of each year was the indicator of bone mass. RESULTS: Most boys (87.8%) met Canadian recommendations for milk product intake. Few subjects (<30%) consumed vegetables and fruit in recommended amounts. Using a multilevel modeling statistical approach containing important biological and environmental factors, we found that vegetable and fruit intakes, calcium intake, and physical activity were significant independent environmental predictors of TBBMC in boys but not in girls. CONCLUSIONS: In addition to adequate dietary calcium intake, appropriate intakes of vegetables and fruit have a beneficial effect on TBBMC in boys aged 8-20 y. Underreporting of dietary intake by girls may explain why this effect was not apparent in girls.

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.

The 'muscle-bone unit' during the pubertal growth spurt.

Mechanostat theory postulates that developmental changes in bone strength are secondary to the increasing loads imposed by larger muscle forces. Therefore, the increase in muscle strength should precede the increase in bone strength. We tested this prediction using densitometric surrogate measures of muscle force (lean body mass, LBM) and bone strength (bone mineral content, BMC) in a study on 70 boys and 68 girls who were longitudinally examined during pubertal development. On the level of the total body, the peak in LBM accrual preceded the peak in BMC accretion by an average of 0.51 years in girls and by 0.36 years in boys. In the arms, the maximal increase in LBM was followed by arm peak BMC accrual after an interval of 0.71 years in girls and 0.63 years in boys. In the lower extremities, the maximal increase in LBM was followed by peak BMC accrual after an interval of 0.22 years in girls and 0.48 years in boys. A multiple regression model revealed that total body peak LBM velocity, but not peak height velocity and sex, was independently associated with total body peak BMC velocity (r(2) = 0.50; P < 0.001). Similarly, arm and leg peak LBM velocity, but not peak height velocity and sex, were independently associated with arm and leg peak BMC velocity, respectively (r(2) = 0.61 for arms, r(2) = 0.41 for legs; P < 0.001 in both cases). These results are compatible with the view that bone development is driven by muscle development, although the data do not exclude the hypothesis that the two processes are independently determined by genetic mechanisms.

Factors that affect bone mineral accrual in the adolescent growth spurt.

The development of bone mass during the growing years is an important determinant for risk of osteoporosis in later life. Adequate dietary intake during the growth period may be critical in reaching bone growth potential. The Saskatchewan Bone Mineral Accrual Study (BMAS) is a longitudinal study of bone growth in Caucasian children. We have calculated the times of maximal peak bone mineral content (BMC) velocity to be 14.0 +/- 1.0 y in boys and 12.5 +/- 0.9 y in girls; bone growth is maximal approximately 6 mo after peak height velocity. In the 2 y of peak skeletal growth, adolescents accumulate over 25% of adult bone. BMAS data may provide biological data on calcium requirements through application of calcium accrual values to factorial calculations of requirement. As well, our data are beginning to reveal how dietary patterns may influence attainment of bone mass during the adolescent growth spurt. Replacing milk intake by soft drinks appears to be detrimental to bone gain by girls, but not boys. Fruit and vegetable intake, providing alkalinity to bones and/or acting as a marker of a healthy diet, appears to influence BMC in adolescent girls, but not boys. The reason why these dietary factors appear to be more influential in girls than in boys may be that BMAS girls are consuming less than their requirement for calcium, while boys are above their threshold. Specific dietary and nutrient recommendations for adolescents are needed in order to ensure optimal bone growth and consolidation during this important life stage.

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.

Secular trend in the development of fatness during childhood and adolescence.

This study examined the development of fatness, as indexed by skinfold thickness, in healthy Caucasian children and adolescents residing in the same location in Canada in the 1960s and the 1990s. The data comes from two longitudinal studies, conducted approximately 30 years apart, of children aged 8-16 years. The first study (1964-1973) annually measured 207 males and 140 females. The second investigation (1991-1997) repeatedly measured 113 males and 115 females. Identical measurement tools and protocols were used for height, body mass, and skinfolds. Maturational age was estimated as a measure in years from age of peak height velocity. Males from the second investigation matured significantly (P < 0.05) earlier. Multilevel regression modeling was utilized to determine developmental curves for the individuals within the two populations. When differences in height, body mass, and maturity were controlled, skinfold thicknesses of the males and females in the second study were significantly greater (P < 0.05) than age- and sex-matched peers in the first study. This was not seen in models of the BMI. The results suggest that when maturity and size were controlled, the fatness of children and adolescents increased over 30 years.