The relationship between body composition and onset of menarche.

BACKGROUND: A late age of menarche in elite adolescent athletes is frequently attributed to low body fat/weight. If a critical body weight/fat is necessary for menarche, a reduction in the variability of these parameters would be observed at menarche compared to times before and after this event. AIM: The study determined the variability in body mass (BM), per cent body fat (%BF) and total body fat (TBF) of girls between -2 and +2 years from menarche. METHODS: Participants were part of the Saskatchewan Pediatric Bone Mineral Accrual Study (1991-1998). Body composition was assessed using dual X-ray absorptiometry (DXA). An individual's data was retained for analysis if they had at least four DXA scans between -3 and +3 years from menarche. Values were interpolated from the cubic spline at whole years between -2 and +2 years from menarche. Coefficient of variation (CV) was used to assess variability. RESULTS/CONCLUSION: Data on 61 girls were retained for analysis. The range in BM, TBF and %BF at menarche was 50.10 kg, 35050.06 g and 31.61%, respectively. Reductions in variability of body fat and weight were not apparent at menarche, which does not provide support for the hypothesis that a critical body weight/fat is required for menarche.

Dancing for bone health: a 3-year longitudinal study of bone mineral accrual across puberty in female non-elite dancers and controls.

INTRODUCTION: Weight-bearing exercise during growth enhances peak bone mass. However, the window of opportunity for optimizing positive effects of exercise on peak bone mass remains to be fully defined. Ballet dancing provides a model of mechanical loading patterns required to site-specifically modulate bone. METHODS: We assessed the effects of ballet dancing on bone mineral accrual in female non-elite dancers and normally active controls for 3 years across puberty. We recruited 82 ballet dancers and 61 controls age 8-11 years at baseline. Participants were measured over 3 consecutive years; however, the overlap in ages allowed analysis of the groups across 8-14 years of age. We annually assessed bone mineral content (BMC) at the total body (TB), including upper and lower limb regions, and biannually assessed BMC at the proximal femur and lumbar spine (LS) using dual x-ray absorptiometry (DXA). We derived TB lean mass and fat mass from DXA TB scans. Anthropometry, exercise levels, and calcium intake were also measured biannually. Maturational age was determined by age at peak height velocity (PHV). A multilevel regression model was used to determine the independent effects of body size, body composition, maturation, exercise levels, and calcium intake at each measurement occasion. RESULTS: When adjusted for growth and maturation, dancers had significantly greater BMC at the TB, lower limbs, femoral neck (FN), and LS than controls. Excepting the FN region, these differences became apparent at 1 year post-PHV, or the peripubertal years, and by 2 years post-PHV the differences represented a cumulative advantage in dancers of 0.6-1.3% (p<0.05) greater BMC than controls. At the FN, dancers had 4% (p<0.05) greater BMC than controls in prepuberty and maintained this advantage throughout the pubertal years. CONCLUSIONS: Results from this novel population provide evidence for modest site-specific and maturity-specific effects of mechanical loading on bone.

Limitations to the use of secondary sex characteristics for gender comparisons.

BACKGROUND: To control for the confounding effect of maturation many researchers use secondary sex characteristics to compare individuals within and between genders. However, this assumption presumes that the timing and tempo of secondary sex characteristics is identical in both genders. AIM: The study investigated the timing and relationships between sexual and somatic maturation indices between and within genders. SUBJECTS AND METHODS: Eighty three boys and 75 girls, aged between 8 and 15 years at study entry, were measured every 6 months for 6 consecutive years. Sexual maturation was assessed through pubic hair, facial hair and axillary hair development in boys, and pubic hair development and menarcheal status in girls. Somatic maturation was assessed through age at peak height velocity (PHV). RESULTS: Low to moderate correlations (r = 0.30-0.55, p < 0.05) existed between age of PHV and age of reaching each pubic hair stage. The majority of boys reached PHV in pubic hair stage 4 (79.2%). The majority of girls reached PHV in pubic hair stage 3 (42.5%) and pubic hair stage 4 (47.5%). CONCLUSION: Boys and girls differ in the timing and tempo of somatic and sexual maturity. Thus boys and girls should not be aligned on secondary sex characteristics when controlling for the confounding effects of maturity.

A longitudinal analysis of sex differences in bone mineral accrual in healthy 8-19-year-old boys and girls.

BACKGROUND: Although early in life there is little discernible difference in bone mass between boys and girls, at puberty sex differences are observed. It is uncertain if these differences represent differences in bone mass or just differences in anthropometric dimensions. AIM: The study aimed to identify whether sex independently affects bone mineral content (BMC) accrual in growing boys and girls. Three sites are investigated: total body (TB), femoral neck (FN) and lumbar spine (LS). SUBJECTS AND METHODS: 85 boys and 67 girls were assessed annually for seven consecutive years. BMC was assessed by dual energy X-ray absorptiometry (DXA). Biological age was defined as years from age at peak height velocity (PHV). Data were analysed using a hierarchical (random effects) modelling approach. RESULTS: When biological age, body size and body composition were controlled, boys had statistically significantly higher TB and FN BMC at all maturity levels (p < 0.05). No independent sex differences were found at the LS (p > 0.05). CONCLUSION: Although a statistical significant sex effect is observed, it is less than the error of the measurement, and thus sex difference are debatable. In general, sex difference are explained by anthropometric difference.

Timing and magnitude of peak height velocity and peak tissue velocities for early, average, and late maturing boys and girls.

Height, weight, and tissue accrual were determined in 60 male and 53 female adolescents measured annually over six years using standard anthropometry and dual-energy X-ray absorptiometry (DXA). Annual velocities were derived, and the ages and magnitudes of peak height and peak tissue velocities were determined using a cubic spline fit to individual data. Individuals were rank ordered on the basis of sex and age at peak height velocity (PHV) and then divided into quartiles: early (lowest quartile), average (middle two quartiles), and late (highest quartile) maturers. Sex- and maturity-related comparisons in ages and magnitudes of peak height and peak tissue velocities were made. Males reached peak velocities significantly later than females for all tissues and had significantly greater magnitudes at peak. The age at PHV was negatively correlated with the magnitude of PHV in both sexes. At a similar maturity point (age at PHV) there were no differences in weight or fat mass among maturity groups in both sexes. Late maturing males, however, accrued more bone mineral and lean mass and were taller at the age of PHV compared to early maturers. Thus, maturational status (early, average, or late maturity) as indicated by age at PHV is inversely related to the magnitude of PHV in both sexes. At a similar maturational point there are no differences between early and late maturers for weight and fat mass in boys and girls.

A six-year longitudinal study of the relationship of physical activity to bone mineral accrual in growing children: the university of Saskatchewan bone mineral accrual study.

To investigate the influence of physical activity on bone mineral accrual during the adolescent years, we analyzed 6 years of data from 53 girls and 60 boys. Physical activity, dietary intakes, and anthropometry were measured every 6 months and dual-energy X-ray absorptiometry scans of the total body (TB), lumbar spine (LS), and proximal femur (Hologic 2000, array mode) were collected annually. Distance and velocity curves for height and bone mineral content (BMC) were fitted for each child at several skeletal sites using a cubic spline procedure, from which ages at peak height velocity (PHV) and peak BMC velocity (PBMCV) were identified. A mean age- and gender-specific standardized activity (Z) score was calculated for each subject based on multiple yearly activity assessments collected up until age of PHV. This score was used to identify active (top quartile), average (middle 2 quartiles), or inactive (bottom quartile) groups. Two-way analysis of covariance, with height and weight at PHV controlled for, demonstrated significant physical activity and gender main effects (but no interaction) for PBMCV, for BMC accrued for 2 years around peak velocity, and for BMC at 1 year post-PBMCV for the TB and femoral neck and for physical activity but not gender at the LS (all p < 0.05). Controlling for maturational and size differences between groups, we noted a 9% and 17% greater TB BMC for active boys and girls, respectively, over their inactive peers 1 year after the age of PBMCV. We also estimated that, on average, 26% of adult TB bone mineral was accrued during the 2 years around PBMCV.

Peak bone mineral accrual and age at menarche in adolescent girls: a 6-year longitudinal study.

BACKGROUND AND OBJECTIVES: The greatest increase in bone mineral content occurs during adolescence. The amount of bone accrued may significantly affect bone mineral status in later life. We carried out a longitudinal investigation of the magnitude and timing of peak bone mineral content velocity (PBMCV) in relation to peak height velocity (PHV) and the age at menarche in a group of adolescent girls over a 6-year period. METHODS: The 53 girls in this study are a subset of the 115 girls (initially 8 to 16 years) in a 6-year longitudinal study of bone mineral accretion. The ages at PBMCV and PHV were determined by using a cubic spline curve fitting procedure. Determinations were based on height (n = 12) and bone (n = 6) measurements over 6 years. RESULTS: The timing of PBMCV and menarche were coincident, preceded approximately 1 year earlier by PHV. Correlation showed a negative relationship between age at menarche and both peak bone mineral accrual (r = -0.42, P < .002) and PHV (r = -0.45, P < .001). CONCLUSIONS: This longitudinal study demonstrated the close association between age at PBMCV and age at menarche and confirmed the relationship between greater PBMCV and PHV in earlier, as compared with later, maturing girls.

Seasonal height velocity variation in boys and girls 8-18 years.

This study investigated the seasonal variation in height velocity during the summer and winter months. The subjects were healthy children, 109 boys and 119 girls, 8.5-18.0 years of age who are part of an ongoing longitudinal study of bone mineral accrual. Anthropometric dimensions were taken twice a year, in the fall in conjunction with the annual bone assessment measures and 6 months later. Six-month velocities for height were calculated, which produced 982 velocities in boys and 1043 velocities in girls. Over the age range studied, summer velocities accounted for at least 67% of the total yearly growth in boys and 60% of the total yearly growth in girls. Separate two-way ANOVAs (season by age) were used to compare the summer and winter velocities over half-yearly age increments in both sexes. Season and age effects were significant (P < 0.01), but the interaction effect was not significant. The seasonal differences converged in the later years when the summer and winter velocities decreased to zero. The results demonstrate the importance of considering seasonal variation in height velocity in designing studies and in assessing and interpreting growth data. Am. J. Hum. Biol. 9:709-715, 1997. © 1997 Wiley-Liss, Inc.

Somatotypes of 7- to 16-year-old boys in Saskatchewan, Canada.

The purpose of this study was to examine the stability of somatotypes of 63 boys in Saskatoon, Canada who were followed from 7 to 16 years of age. Somatotype photos were taken annually and rated by a criterion rater (BH-R). Comparisons were made longitudinally across all years using repeated-measures ANOVAs of the whole somatotype (S), somatotype attitudinal means (SAM), analysis of categories, separate components (endomorphy, mesomorphy, ectomorphy), and partial correlations. In the first year, the means were age = 7.1 yr, height = 121.0 cm, mass = 22.8 kg, S = 2.9-3.6-1.6, and SAM = 1.1. In the last year, the means were age = 16.7 yr, height = 172.6 cm, mass = 59.9 kg, S = 2.5-4.0-3.7, and SAM = 1.4. Mean somatotypes across years were different [F(9,558) = 67.9, P < .01], with the largest differences between 7-10 yr and 14-16 yr. These differences were largely due to significant increases in mesomorphy (F = 24.6, P < .01) and ectomorphy (F = 159.9, P < .01). Partial correlations between ages for each component, with the other two held constant, revealed poor predictions for three or more years apart (r2 < .35). Thus, both group and individual somatotypes changed between 7 and 16 years of age. The overall pattern was from endo-mesomorph through central to mesomorph-ectomorph somatotypes. The trends are similar to those observed in comparable samples from other countries. Am. J. Hum. Biol. 9:257-272, 1997. © 1997 Wiley-Liss, Inc.

The application of new height-prediction equations (Tanner-Whitehouse mark 2) to a sample of Canadian boys.

The adult statures of a sample of 71 Canadian boys from the Saskatchewan Longitudinal Growth Study were predicted using the original TW Mark 1 and the new TW Mark 2 prediction equations. The subjects had a mean chronological age of 11.59 years (SD = 0.30), a mean RUS bone age of 11.62 'years' (SD = 1.18), a mean height of 145.0 cm (SD = 6.98) and a mean measured adult height of 177.2 cm (SD = 6.65). The Mark 2 equations improved the predictions over Mark 1 by an average of 0.2-0.6 cm and slightly reduced the range of errors. No improvement in the prediction of boys above the 75th centile of British standards was noted but 60-70% of boys below the 25th centile predicted better with the Mark 2 equations. This pattern may well be repeated in more extreme subjects. About 80% of individuals who predicted badly with the Mark 1 equations, i.e. with errors equal to or greater than 5 cm, improved their predictions when Mark 2 equations were used.

Longitudinal comparison of aerobic power in active and inactive boys aged 7.0 to 17.0 years.

Height and maximal aerobic power (VO2 max) were analysed longitudinally in 14 active and 11 inactive boys from the Saskatchewan Longitudinal Growth Study. VO2 max values were obtained from a treadmill run repeated each year. The Preece-Baines Model I was fitted to height and VO2 max values over the duration of the study. No significant differences were found for height attained between the two groups. VO2 max comparisons revealed no significant differences before the take-off point for the adolescent growth spurt. Significant differences occurred in the VO2 max attained by the age of peak adolescent velocity in VO2 max, the increase from take-off to peak and in the adult value, with active boys having higher values. It is concluded that activity before adolescence causes no significant increase in VO2 max, but that adolescence is the critical period during which consistently higher rates of increase in the VO2 max of active boys result in a significantly greater adult value.

Development of the Canadian Home Fitness Test.

The Canadian Home Fitness Test is a self-administered procedure in which the participant steps at an age- and sex-specific rhythm controlled by recorded music, then palpates the pulse immediately following activity. Validation of the test has shown a correlation of 0.72 with the results of a standard submaximum bicycle ergometer test, while the directly measured maximum oxygen intake is correlated even more closely (r = 0.88) with the attained stepping rate, body weight and recovery heart rate. Given modest training, subjects could measure their immediate postexercise heart rate (correlation with electro-cardiographic data, r = 0.94), although 10-second counts underestimated the true rate by an average of 7 beats/min. The safety of the test will be established ultimately by experience in its use in a large population; nevertheless, both theoretical considerations and results of trials in over 14 000 adults suggest the procedure can be self-administered without serious consequences. It is also well accepted by the general public and arouses considerable interest in most homes. The test can thus be recommended as providing an approximate measure of an individual's physical fitness in order to stimulate an increase in personal physical activity. It also has potential as a simple screening procedure that would allow paramedical personnel to record fitness levels and standardized exercise electrocardiograms in large segments of the population.

A current view of Canadian cardiorespiratory fitness.

A standard Astrand bicycle ergometer test was used to predict the maximum oxygen intake of 672 female and 558 male volunteers ranging in age from 15 to 69 years. In terms of this index of cardiorespiratory performance Canadians were unfit relative to Swedish norms. Also, some 47% of women and 40% of men achieved only low or fair fitness categories when evaluated relative to American Heart Association recommendations. These results are poorer than those reported for Torontonians in 1966. Men perceive their cardiorespiratory fitness accurately but women do not. In both sexes adequate recreational activity apparently leads to maintenance of cardiorespiratory fitness.