The relative importance of skeletal age and chronological age in explaining body measurements and the relative importance of skeletal age, chronological age, height, weight, and their interactions in explaining motor fitness components are reported. Anthropometric, motor fitness, and skeletal maturity data have been collected in a mixed longitudinal study of Belgian school boys 12+/- - 19+/- years. At each age level multiple regression equations were calculated to evaluate the relative importance of the independent variables. Skeletal age was assessed by the TW2 method and the anthropometric measurements were taken following standard procedures. The motor fitness tests were selected on their factor loading and reliability in the same age range. Between 13 and 16 years a fairly high percentage of the variation in body dimensions is explained by skeletal age (+/-50% for stature). The percentage of explained variance reaches its maximum at 14-15 years. The highest percentage is found for linear dimensions and weight followed by bone width dimensions and circumferences. Triceps and calf skinfolds are not related to skeletal age. Chronological age as such does not contribute in the prediction of body measurements. The interaction between chronological age and skeletal age as such or in combination with height and/or weight have the highest predictive value except for trunk strength (leg lifting) and functional strength (bent arm hang). Except for static strength (arm pull), for which the explained variance ranged from 33% to 58%, the predictive value of body size, maturity, chronological age and their interactions is rather low, varying between 0% and 17%. As for body dimensions, the explained variance reaches its maximum for most motor tests at 14-15 years.

Relationships between fatness and skeletal maturity are considered in a nationwide sample of 14,259 Belgian boys 12 through 17 years of age (The Leuven Growth Study of Belgian Boys). Absolute fatness was estimated from four skinfolds using the Drinkwater and Ross technique and from the sum of four skinfolds, and was related to skeletal maturity assessed by the Tanner-Whitehouse method (I and II). In addition, comparisons were made between the fattest 5% and leanest 5% of the boys at each age level. Correlations between the indices of fatness and skeletal age and relative skeletal age (the difference between skeletal and chronological ages) are positive and generally low, ranging from 0.12 to 0.39. They tend to decrease with age from 12 to 17 years. Comparisons between the extreme groups indicate that the leanest boys are more delayed in skeletal maturity, by about 0.8 years, than the fattest boys are advanced, by about 0.5 years. Stature data for the same boys are consistent with the skeletal maturity data and thus suggest that the size differences between the extreme groups are due in part to maturity differences. Over the age span 12 through 20 years, the leanest boys are reduced in stature by about -1.2 standard deviations, while the fattest boys are larger in stature by about +0.6 standard deviation units. The size differences, however, persist after skeletal maturity is attained so that there may be a specific role for fatness in influencing statural growth.

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A 1 year prospective study was done to develop an accident-prone and overuse-prone profile of young athletes. A group of 185 freshman physical education students (118 males; 67 females of the same age (18.3 +/- 0.5 years) trained under the same conditions and were exposed to similar extrinsic risk factors. Using a descriptive statistical technique, an analysis of correspondence, the complex interrelation between the criterium variables (acute injuries and overuse injuries) and the predictor variables (intrinsic risk factors; physical characteristics--anthropometric data, physical fitness parameters, flexibility aspects and malalignment of the lower extremities; and psychological factors--16 personality traits) was estimated for males and females separately. Although dynamic strength seems to be an important risk factor in acute injuries, sports accidents must be seen in relation to psychological factors. However, the overuse-prone profile is mainly based on physical traits: a combination of muscle weakness, ligamentous laxity, and muscle tightness predisposes to stress injuries. In addition, these overuse effects are intensified by large body weight and length, a high explosive strength, and malalignment of the lower limbs. Nevertheless, it has to be kept in mind that psychosomatic factors play a role in how one experiences these overuse phenomena.

limb movement, explosive strength and static strength are neg atively related to APHV; thus, early maturers performed better than late maturers. However, between late adolescence and adulthood (30 years), the late maturers not only caught up to the early maturers, but there were significant differences for explosive strength and functional strength in favor o f late ma turers. Finally, age-specific tracking, using inter-age correla tions, of adult health-and performance-related fitness scores were investigated. In addition, the independent contribution of adolescent physical characteristics to the explanation of adult fitness scores was also studied. Tracking between age 13 and age 30 years was moderately high (46% of variance explained) for flexibility, low to moderate (between 19% and 27% of var iance explained) for the other fitness parameters and low for pulse recovery and static strength (7% to 11% of variance ex plained). Between age 18 and age 30 years the tracking was high for flexibility, moderately high for explosive and static strength, and moderate for the other fitness parameters except for pulse recovery. The amount of variance of adult fitness lev els explained increased significantly when other characteristics observed during adolescence entered the regressions or discri minant functions. N