Lean body mass and leg power best predict bone mineral density in adolescent girls

PURPOSE: We evaluated anthropometric and performance measures that best predict bone mineral density (BMD) and bone mineral content (BMC) in 54 adolescent girls (14.6 +/- 0.5 yr; 22.7 +/- 14.0 months past menarche). METHODS: Whole body, femoral neck, greater trochanter, lumbar spine (L2-L4), and mid-femoral shaft BMD and BMC, and whole body bone-free lean mass and fat mass were assessed using DXA (Hologic QDR 1000/W). Knee extensor strength and leg power were assessed by isokinetic dynamometry and the Wingate Anaerobic Power Test, respectively. RESULTS: Whole body lean mass was correlated with BMD at all bone sites (r = 0.45-0.77; P < 0.001) and was more highly correlated with bone at all sites than was body weight. Leg power was also associated with BMD at all sites (r = 0.41-0.67; P < 0.001), whereas leg strength correlated significantly with all sites (r = 0.41-0.53; P < 0.001) except the lumbar spine. Stepwise regression analyses revealed that 59% of the variance in whole body BMD was predicted by lean mass alone. No other variables, including fat mass, height, months past menarche, leg power, or leg strength, contributed additionally to the regression model. Similarly, lean mass was the only predictor of lumbar spine and femoral shaft BMD (R2 = 0.25, R2 = 0.37, respectively), while femoral neck and trochanteric BMD were best predicted by leg power (R2 = 0.38, R2 = 0.36, respectively). Similar but stronger models emerged using BMC as the outcome, with lean mass and leg power explaining the most variance in BMC values. CONCLUSION: In this group of adolescent girls, lean body mass and leg power best predicted BMC and BMD of the whole body, lumbar spine, femoral shaft, and hip, which may suggest an important role for muscle mass development during growth to maximize peak bone density.     

Muscular development and physical activity as major determinants of femoral bone mass acquisition during growth

Objectives: To investigate to what extent bone mass accrual is determined by physical activity and changes in lean, fat, and total body mass during growth. Methods: Twenty six physically active and 16 age matched control boys were followed up for three years. All subjects were prepubertal at the start of the survey (mean (SEM) age 9.4 (0.3) years). The weekly physical activity of the active boys included compulsory physical education sessions (80–90 minutes a week), three hours a week of extracurricular sports participation, and occasional sports competitions at weekends. The physical activity of the control group was limited to the compulsory physical education curriculum. Bone mineral content (BMC) and areal density (BMD), lean mass, and fat mass were measured by dual energy x ray absorptiometry. Results: The effect of sports participation on femoral bone mass accrual was remarkable. Femoral BMC and BMD increased twice as much in the active group as in the controls over the three year period (p<0.05). The greatest correlation was found between the increment in femoral bone mass and the increment in lean mass (BMC r = 0.67 and BMD r = 0.69, both p<0.001). Multiple regression analysis revealed enhancement in lean mass as the best predictor of the increment in femoral bone BMC (R = 0.65) and BMD (R = 0.69). Conclusions: Long term sports participation during early adolescence results in greater accrual of bone mass. Enhancement of lean mass seems to be the best predictor of this bone mass accumulation. However, for a given muscle mass, a greater level of physical activity is associated with greater bone mass and density in peripubertal boys.     

青春前期和早期女性血清维生素D、雌二醇和瘦体重含量与骨骼发育的相关性研究

目的:研究女性从青春前期到初潮腰椎、股骨颈的发育特征及主要影响因素。方法:201名身体健康的女性(10.9±0.7岁)自愿参加本项实验研究并进行体质测量,主要测量脂肪含量(FM)、瘦体重含量(LM)、以及股骨颈(Fn)和腰椎(Ls)骨密度(BMD)、骨量(BMC)和骨面积(BA)。同时检测血清雌二醇(E2)、类胰岛素样生长因子1(IGF-1)、睾酮(T)和维生素D(VD)等。追踪获得受试者初潮的时间,以此作为时间参考来拟合骨骼的最佳生长曲线。采用stepwise forward多元回归方法来确定腰椎、股骨颈的影响因素。结果:①初潮之前快速增长的股骨颈和腰椎各项指标在初潮之后却出现不同的变化趋势:股骨颈BMD、BMC提高了增长速度;而股骨颈和腰椎BA减慢了增长速度;腰椎BMD、BMC继续保持原有的增长速度。②E2是预测股骨颈BMD和腰椎BMD、BMC增长的重要因子,而VD是预测股骨颈和腰椎BMC、BA变化的重要因素。LM则是预测股骨颈和腰椎BMD、BMC和BA发育的重要因素。结论:女性初潮之前是腰椎、股骨颈的骨面积快速生长时期,而初潮之后则是矿物质积累增长的关键时期。血清维生素D、雌二醇水平与瘦体重含量是女性快速生长时期骨骼发育和矿物质沉积的重要调节因素。     

Whole-body bone mineral content, lean body mass, and fat mass measured by dual-energy X-ray absorptiometry in a population of normal Canadian children and adolescents.

Measurements of body composition have evident value in evaluating growing children and adolescents, and dual-energy X-ray absorptiometry (DXA) is a tool that provides accurate measurements of whole-body bone mineral content (WBBMC), lean body mass (LBM), and fat mass (FM). To interpret such measurements in the context of ill health, normative values must be available. Such information could be expected to be regionally specific because of differences in ethnic, dietary, and physical activity determinants. In this study, DXA was performed with Hologic densitometers in normal girls (n = 91) and boys (n = 88) between 3 and 18 years of age. The derivation of normal ranges is presented for boys and girls. The correlation of the sum of WBBMC, LBM, and FM with directly measured body weight was almost perfect (r > 0.997). As expected, FM and body mass index correlated strongly. The normal values for WBBMC, LBM, and FM from this study are compared with other Canadian data and with published normative data from Argentina and the Netherlands, all of which use different densitometers. The results of this study allow the calculation of z scores for each facet of body composition and facilitate the use of DXA to report routine evaluations of body composition in children and adolescents.     

Maximum oxygen uptake and objectively measured physical activity in Danish children 6-7 years of age: the Copenhagen school child intervention study

Objectives: To provide normative data on maximum oxygen uptake (V^·O₂MAX) and physical activity in children 6–7 years of age and analyse the association between these variables. Methods: V^·O₂MAX was measured in 366 boys (mean (SD) 6.8 (0.4) years of age) and 332 girls (6.7 (0.4) years of age) from preschool classes in two suburban communities in Copenhagen, during a progressive treadmill exercise. Habitual physical activity was measured with accelerometers. Results: Boys had higher V^·O₂MAX both in absolute values (1.19 (0.18) v 1.06 (0.16) litres/min (+11%), p<0.001) and relative to body weight (48.5 (6.0) v 44.8 (5.6) ml/kg/min (+8%); p<0.001) than girls. The difference in V^·O₂MAX between boys and girls decreased to +2% when expressed relative to lean body mass (LBM). Absolute V^·O₂MAX was related to LBM, body mass, and stature (all p<0.001). Boys were more physically active than girls (mean counts +9.4%, p<0.001), and even when boys and girls with the same V^·O₂MAX were compared, boys were more active. The difference in physical activity between the sexes was higher when sustained activity of higher intensity was compared. Conclusions: V^·O₂MAX is higher in boys than girls (+11%), even when related to body mass (+8%) and LBM (+2%). Most of the difference in V^·O₂MAX relative to body mass was explained by the larger percentage body fat in girls. When boys and girls with the same V^·O₂MAX were compared, boys engaged in more minutes of exercise of at least moderate intensity.     

"Bounce at the Bell": a novel program of short bouts of exercise improves proximal femur bone mass in early pubertal children

Objectives: To examine the effects of a simple and inexpensive physical activity intervention on change in bone mass and structure in school aged children. Methods: Fifty one children (n = 23 boys and 28 girls; mean age 10.1 years) participated in "Bounce at the Bell" which consisted of 10 counter-movement jumps 3x per day (total ∼3 min/day). Controls were 71 matched children who followed usual school practice. We assessed dietary calcium, physical activity, physical performance, and anthropometry in September and after 8 months of intervention (June). We measured bone mineral content (BMC) and bone area at the lumbar spine, total body, and proximal femur. Proximal femur scans were also analysed for bone geometry and structural strength using the hip structural analysis program. Lean and fat mass (g) were also calculated. Results: Groups were similar at baseline and did not differ in weight, height, total body, lumbar spine, proximal femur, or femoral neck BMC. Control children had a greater increase in adjusted total body BMC (1.4%). Intervention children gained significantly more BMC at the total proximal femur (2%) and the intertrochanteric region (27%). Change in bone structural parameters did not differ between groups. Conclusions: This novel, easily implemented exercise program, took only a few minutes each day and enhanced bone mass at the weight bearing proximal femur in early pubertal children. A large, randomised study of boys and girls should be undertaken powered to test the effectiveness of Bounce at the Bell in children at different stages of maturity, and in boys and girls independently.     

Resting energy expenditure: a better marker than BMI for BMD in African-American women

PURPOSE: African-American women tend to be more overweight and to have lower resting energy expenditures (REE) compared with Caucasian women. Weight is associated with bone mineral density (BMD), but the relation between BMD and REE has not been reported. METHODS: Four hundred postmenopausal African-American women aged 45-87 (yr) from San Diego, CA participated in this community-based cross-sectional study. Body composition (fat mass, lean body mass), bone mineral content (BMC) and BMD of the lumbar spine, hip (femoral neck, greater trochanter, intertrochanter), and total body were measured using dual energy x-ray absorptiometry (DXA). REE was calculated using the Harris-Benedict equation; grip strength was measured by isometric dynamometry. RESULTS: REE (r range: 0.32-0.79) showed the strongest correlation with spine, total hip, and total body BMC and BMD. In stepwise multiple linear regressions adjusted for age and grip strength, REE explained 15% of the variance in spine BMD, 33% of the variance in total hip, and 32% of the total body BMD variance. REE explained 63% of the total body BMC variance. When body weight replaced REE in the models, weight became the strongest covariate of BMC and BMD but explained 1% less of the variance in spine BMD, 5% less of the variance in total hip BMD, 4% less of the variance in total body BMD, and 3% less of the variances in spine, total hip, and total body BMC than did REE. CONCLUSION: In this cohort of African-American women, weight explained less of the BMC and BMD variance than REE. Poor energy economy may contribute to being overweight and may explain the lower rates of osteoporosis observed in African-American women.     

Bone mineral content and density of Tunisian male rugby players: differences between forwards and backs

The purpose of this study was to examine the effects of long-term rugby participation on bone mineral content (BMC) and density (BMD) of male rugby players and to determine if the diverse stimuli elicited by the actions of forwards and backs affect their skeleton differently. Dual energy X-ray absorptiometry (DXA) scans were obtained from 20 male rugby players (10 Forwards and 10 Backs) who actively participated in rugby for the past 13 yr, and from 29 age matched non active subjects of the same ethnic origin. Both groups (rugby players and controls) had comparable age (23.6 +/- 3.7 yr vs. 25.6 +/- 3.4 yr), height (178.1 +/- 4.0 cm vs. 178.3 +/- 6.0 cm), and body fat percentage (14.2 +/- 4.4 vs. 16.5 +/- 5.1). Rugby players showed greater total body mass, and greater total lean and fat body masses than control subjects (p < 0.01). Whole spine BMC and BMD were 52 % and 15 % higher, respectively, in the rugby players than in the control subjects (p < 0.001). Furthermore, rugby players displayed higher skeletal BMC (40 %, 37 % and 58 % for legs, arms and pelvis, respectively) and BMD (16 %, 21 % and 17 %, respectively) than controls. Within the rugby group, forwards were taller, heavier and had greater body fat percentage, and greater total lean and fat body masses than backs (p < 0.05 to p < 0.001). Likewise, BMC, BMD and bone area for the whole body and at specific sites such as arms, spine and legs were also greater in the forwards (p < 0.05 to p < 0.001). Long-term rugby participation, starting at pubertal age, is associated with markedly increased BMC, BMD and bone size at all skeletal sites, except at the head. The musculo-skeletal adaptations, greater in forwards than in backs, could mimic training responses and therefore explain the bone features, localized in specific stressed regions.     

Consideration of the canalisation effect based on physical factors of mothers and their children

The canalisation effect refers to the finding that there is less variance from one’s genetically predisposed growth in girls than in boys. In this study, the canalisation effect was confirmed by measuring not only the physique of parents and children but also their body composition, and the relationship between body composition of parents and children was investigated. The subjects were 56 mothers aged in their 20s to 40s and their 56 children (boys 29, girls 27). Physique, body composition and bone mineral density were measured in 56 mothers and their children. The influence of age was controlled so that a correlation analysis between children and mothers was possible with the cross-sectional data used in the present study. A correlation analysis between mothers and their children was also conducted with estimated values that were controlled for age. As a result, in the relationship between sons and mothers, significant correlations were seen in height and soft lean mass (SLM), while in the relation between daughters and mothers, significant correlations were seen in everything but bone mineral density; that is, in height, weight, bone mass, SLM, fat mass and body fat percentage. In the relationship between sons and mothers, the correlation in height was strong.     

Lifestyle risk factors for osteoporosis in Asian and Caucasian girls.

PURPOSE: We investigated ethnic differences in areal bone mineral density (aBMD; g x cm(-2)) and its determinants at two levels of maturity in Asian- and Caucasian-Canadian girls. METHODS: Participants were 131 Asian (26 Tanner breast stage I (aTI) and 30 Tanner II (aTII)), and Caucasian (30 Tanner I (cTI) and 45 Tanner II (cTII)) girls. We measured calcium intake by a food frequency questionnaire, general physical activity, and extracurricular sports with a modified Physical Activity Questionnaire for Children and loaded physical activity by 7-d recall. Fat mass, lean mass, and aBMD for the total body (TB), and aBMD at the lumbar spine (LS), proximal femur (PF), femoral neck (FN), and trochanter (TR) were measured by DXA (Hologic QDR 4500). We used ANCOVA (controlling for size and lean and fat mass) to compare bone mineral content (BMC) and aBMD between ethnicities within Tanner stages. RESULTS: Calcium intake was significantly lower for Asian girls in both TI and TII (P < 0.001) as compared with Caucasians. For physical activity measures, only the general score was greater in cTI than aTI (P < 0.05). Participation in loaded physical activities and extracurricular sports was significantly less for aTII than cTII (both, P < 0.01), whereas general physical activity did not differ. aBMD measures were similar between aTI and cTI. However, TB, PF, FN, and aBMD were significantly lower (approximately 9-14%) in aTII as compared with cTII. CONCLUSION: Thus, there was greater ethnic disparity in lifestyle factors related to bone health and absolute measures of bone mineral with advanced maturity.     

女性初潮前后骨代谢生化因子与雌激素、瘦体重相关分析

目的:探讨女性骨代谢生化因子骨钙素(OC)、骨碱性磷酸酶(BAP)和抗酒石酸酸性磷酸酶(TRAP)在初潮前后的变化特征及其相关影响因素。方法:以平均年龄(11.4±0.6)岁的115名小学女生为对象,测量其身高(H)、体重(W)、脂肪含量(FM)、瘦体重含量(LM),血清雌二醇(E2)、睾酮(T)、性激素结合蛋白(SHBG)及血清OC、BAP和TRAP。随访获得实验对象的初潮时间,以测量时相距初潮的时间作为自变量,拟合骨代谢生化因子及相关指标的回归曲线方程。采用偏相关方法检测骨代谢生化标志物与其影响因素之间的相关性。结果:初潮前呈上升趋势的OC、BAP在初潮时显著下降,而TRAP从初潮前至初潮一直下降。从初潮前至初潮,H与BAP(r=0.22,P=0.001)、OC(r=0.21,P=0.002)和TRAP(r=0.14,P=0.04)显著相关,E2、LM与BAP(E2:r=0.2,P=0.003;LM:r=0.15,P=0.029)、OC(E2:r=0.34,P<0.0001;LM:r=0.30,P<0.0001)也显著相关,与TRAP无明显相关。结果表明:女性初潮时骨代谢速度明显减慢,身高增长与骨代谢密切相关,雌激素和瘦体重含量是骨组织代谢的相关影响因素。     

Thicker radial cortex in physically active prepubertal girls compared to controls

This study was carried out to investigate the effects of physical activity on cortical bone of the radius in a population of prepubertal girls. Forty-nine healthy girls, 17 actives (10.62 +/- 1.56 years) and 32 controls (9.84 +/- 1.23 years) participated in this study. The active group was involved in gymnastics, judo, and dance on average 7.76 +/- 3.94 h/week. Bone mineral content (BMC) and density (BMD) were performed at the distal third of the non-dominant radius using DXA. The lean mass of the non-dominant forearm was derived from the total body analysis performed with DXA. In order to obtain bone cortical thickness, standard radiographs of the non-dominant radius were scanned and computed using a software program based on radiogrammetry. BMD and BMC values were higher in actives than in controls. Cortical thickness at the ulnar side correlated significantly with all the anthropometric and densitometric values as well as the duration of training. In addition, cortical thickness at the ulnar side was significantly higher in the actives compared to the controls. After adjustment for the duration of training per week, cortical thickness of the ulnar side did not differ any more between actives and controls. The same observation was obtained after adjustment for the forearm lean mass. In our active population, physical practice seemed to have induced greater BMC and higher cortical thickness than those observed in the sedentary.     

Influence of sports participation and menarche on bone mineral density of female high school athletes

Weight-bearing exercise during adolescence may enhance peak bone mineral density (BMD) and reduce osteoporosis risk. The association of sports participation before and after menarche with areal BMD (by central DXA) was investigated in 99 female high school athletes (age 15.5+/-1.3 year). The frequency and duration of structured sports (school-based or other organized team) were assessed using an interviewer-assisted questionnaire. Overall, the average number of years of weight-bearing sport participation was 7.4+/-3.4 years; 72% of the athletes began sport participation before menarche. Training patterns and BMD were examined by tertiles of yearly weight-bearing sport participation (hours/year) before (WBpre), after (WBpost) menarche, and in total (WBtotal). After adjusting for chronological age, gynecological age, and BMI, compared to athletes in the WBtotal low tertile, athletes in the WBtotal high tertile had significantly greater BMD at the spine (p=0.009), total hip (p=0.03), trochanter (p=0.03), and total body (p=0.009). Similar patterns were found by WBpre or WBpost status, separately, with the exception of spine BMD which was significantly different across tertiles in WBpost only (p<0.01). While the number of years of participation was similar across tertiles of WBtotal, the number of months/year was significantly greater among athletes in the high tertile than athletes in the low tertile (9.2+/-3.4 month/year versus 5.0+/-2.9 month/year, respectively (p<0.001)). These results indicate that near year-round participation in structured weight-bearing sports during early adolescence may help young girls optimize bone mineral accrual during these critical years, and may decrease their risk of osteoporosis with advancing age.     

Psychobiology and behavioral strategies. Physical activity, sport participation, and suicidal behavior: U.S. high school students

PURPOSE: To evaluate the associations of physical activity and sports team participation with suicidal behavior among U.S. high school students. METHODS: Data were from the 2003 Youth Risk Behavior Survey (N = 10,530 respondents). Exposure variables included physical activity (inactive, insufficient, moderately intensive, regular vigorously intensive, and frequent vigorously intensive) and sports team participation. Outcome variables were suicide ideation (seriously considering and/or planning suicide) and suicide attempts. Hierarchical logistic regressions were run, controlling for age, race, smoking, alcohol use, drug use, geographic region, unhealthy weight-control practices, and body mass index/weight perceptions. RESULTS: Compared with inactive students or sports team nonparticipants, the odds of suicide ideation were lower among boys reporting frequent vigorous-intensity physical activity (adjusted odds ratio (AOR) = 0.48; 95% confidence interval (CI) = 0.29, 0.79) and sports team participation, respectively (AOR = 0.65; 95% CI = 0.48, 0.86). The odds of suicide attempts were also lower among frequently vigorously active boys (AOR = 0.44; 95% CI = 0.21, 0.96) and sports team participants (AOR = 0.61; 95% CI = 0.40, 0.93). The odds of suicide attempts were lower for regular vigorously active girls compared with inactive girls (AOR = 0.67; 95% CI = 0.45, 0.99) and sports team participants compared with nonparticipants (AOR = 0.73; 95% CI = 0.57, 0.94). Associations with one exposure variable generally weakened when adjustment was made for the other exposure variable, or for feeling sad and hopeless. CONCLUSIONS: The association of physical activity and sports team participation with suicide ideation and suicide attempts varied by sex. Further research is needed to clarify these different associations.     

Assessment of whole-body composition with dual-energy x-ray absorptiometry.

Dual-energy x-ray absorptiometry (DXA) allows noninvasive direct measurement of the three major components of body composition: lean body mass (LBM), fat body mass (FBM), and bone mineral body mass (BBM). To study the accuracy and short-term and long-term precision of body composition measurements, the authors measured body composition with DXA in 60 healthy young adults. Independent measurement of LBM (LBMK-40), obtained from the determination of the whole-body content of potassium-40 with a whole-body scintillation detector, was highly correlated with LBM determined with DXA (LBMDXA) (LBMK-40 = 1.069.LBMDXA,R2 = .996). Assessment of body composition in 10 patients with acquired immunodeficiency syndrome (AIDS) and 10 patients with cystic fibrosis was performed with DXA. The AIDS patients showed a marked decrease in LBM, while in patients with cystic fibrosis, LBM and BBM were decreased. DXA measurements of body composition appeared accurate and precise enough to be of clinical relevance in detecting specific alterations of body composition.     

High femoral bone mineral density accretion in prepubertal soccer players

PURPOSE: To determine the effect of physical activity on bone mineral accrual during growth in prepuberal boys. METHODS: Seventeen soccer players and 11 matched (physically active) control boys (Tanner 1-2, at the start of the study) were followed over a 3-yr period. Bone mineral content (BMC) and a real density (BMD) was measured by dual-energy x-ray absorptiometry. The maximal positive mechanical impulse (CJipos) and height jumped (Hj) during countermovement vertical jumps were assessed with a plate force. Additionally, 30-m running speed test (T30), 300-m run test (AC), and 20-m shuttle run test (MAP) were performed. RESULTS: The soccer players attained better results in MAP and AC than the controls (P < 0.05). At the end of the follow-up, the controls increased their percentage of body fat in 11 units (P < 0.05) whereas it remained unchanged in the soccer players. Lean body mass increased with growth but more in the soccer players than in the controls (P < 0.05). The soccer players exhibited greater BMC in the legs and greater BMD in all bone-loaded regions at the end of the study (P < 0.05). During these 3 yr, the soccer players gained twice as much femoral neck and intertrochanteric BMC than the control group (P < 0.05) and increased their femoral neck BMD by 10% and their mean hip BMD by a third more than the control group (both P < 0.05). Multiple regression analysis showed that the improvement in T30 and CJipos has predictive value for the enhancement of bone mass in growing boys. CONCLUSION: Long-term soccer participation, starting at a prepubertal age, results in greater improvement of physical fitness, greater acquisition of bone mass and a lower accumulation of body fat.     

Artistic versus rhythmic gymnastics: effects on bone and muscle mass in young girls

We compared 35 prepubertal girls, 9 artistic gymnasts and 13 rhythmic gymnasts with 13 nonphysically active controls to study the effect of gymnastics on bone and muscle mass. Lean mass, bone mineral content and areal density were measured by dual energy X-ray absorptiometry, and physical fitness was also assessed. The artistic gymnasts showed a delay in pubertal development compared to the other groups (p<0.05). The artistic gymnasts had a 16 and 17 % higher aerobic power and anaerobic capacity, while the rhythmic group had a 14 % higher anaerobic capacity than the controls, respectively (all p<0.05). The artistic gymnasts had higher lean mass (p<0.05) in the whole body and the extremities than both the rhythmic gymnasts and the controls. Body fat mass was 87.5 and 61.5 % higher in the controls than in the artistic and the rhythmic gymnasts (p<0.05). The upper extremity BMD was higher (p<0.05) in the artistic group compared to the other groups. Lean mass strongly correlated with bone mineral content (r=0.84, p<0.001), and multiple regression analysis showed that total lean mass explained 64 % of the variability in whole body bone mineral content, but only 20 % in whole body bone mineral density. Therefore, recreational artistic gymnastic participation is associated with delayed pubertal development, enhanced physical fitness, muscle mass, and bone density in prepubertal girls, eliciting a higher osteogenic stimulus than rhythmic gymnastic.     

Maximal anaerobic power: relationship to anthropometric characteristics during growth.

The purpose of this study was to determine the effects of age in relation to anthropometric characteristics upon maximal anaerobic power of legs in sixty-nine young boys aged 11 to 19 years. Maximal anaerobic power (Wmax) was measured by the force-velocity test. Lean body mass (LBM) was determined from all four skin-fold thickness measurements, leg volume (LV) was estimated by anthropometric method, and anthropometric measurements were used to determine total muscular mass (TMM). Wmax increased significantly (F = 44.1, p less than 0.001) between 11 and 19 years and was correlated with LV (r = 0.84) and TMM (r = 0.88). It was most highly correlated with LBM (r = 0.94), which best explained the percentage of the total variance of Wmax (88%). Normalized Wmax (Wmax/LBM) also increased significantly between 11 and 19 years (F = 21.9, p less than 0.001). In conclusion, Wmax determined by the force-velocity test was closely related to anthropometric characteristics, especially LBM, during the growth period. Furthermore, even when corrected for lean body mass, maximal anaerobic power was always found to increase. This suggests that other undetermined factors, in addition to the amount of lean tissue mass, may explain the increase of Wmax during the force-velocity test.     

Influence of activity patterns in fitness during youth

The aim of this study was to analyze longitudinal associations between cardiorespiratory fitness, physical activity and body mass index in a 4-year longitudinal study. 170 students (97 girls and 73 boys) aged at baseline from 11 to 17 years were followed. Students performed 20-m-SR; physical activity patterns and parents' education were evaluated using a standard questionnaire. Body mass index was categorized according to established cut points. In a multilevel analysis using MLwIN, 2 level structures were defined: first for individuals and second for time observations. In a longitudinal 2 level analysis, cardiorespiratory fitness was -negatively associated with body mass index for girls and boys, respectively (p<0.05; R2=0.63; 0.62), especially with obesity category (p<0.01; R2=0.58; 0.60). In girls, independent associations were observed between CRF and PA categories regarding participation "almost every day" in organized (p<0.05; R2=0.50) and non-organized sports outside school (p<0.05; R2=0.52) and participation in sports competitions (p<0.05; R2=0.51). In boys, associations were found only with participation in sports competitions (p<0.05; R2=0.50). The results highlight the importance of youth participation in organized activities and competitive sports over time to achieve health-related fitness benefits.     

Body composition of elite American athletes

Five hundred twenty-eight male athletes participating in 26 Olympic events and 298 female athletes participating in 15 Olympic events underwent determination of body fat percentage (% fat) and lean body mass (LBM) via hydrostatic weighing and/or anthropometric methods. All groups of athletes were below the average values for % fat of college age men and women of 15% and 25%, respectively. In general, athletes involved in a sport where their body weight is supported, such as canoe and kayak (males, 13.0 +/- 2.5%; females, 22.2 +/- 4.6%) and swimming (males, 12.4 +/- 3.7%; females 19.5 +/- 2.8%), tended to have higher % fat values. Athletes involved in sports where a weight class has to be made to compete, such as boxing (males, 6.9 +/- 1.6%) and wrestling (male, Junior World Freestyle 7.9 +/- 2.7%), events such as the 100, 200, and 400 meters in athletes (male 100 and 200 meters, 6.5 +/- 1.2%; female 100, 200 and 400 meters, 13.7 +/- 3.6%) that are very anaerobic in nature and extremely aerobic events such as the marathon (males, 6.4 +/- 1.3%) demonstrated lower % fat values. Athletes involved in sports where body size is a definite advantage, such as basketball (males, 84.1 +/- 6.2 kg; females, 55.3 +/- 4.9 kg) and volleyball (males, 75.0 +/- 6.6 kg; females, 58.4 +/- 4.5 kg) tended to have a larger LBM.