Chronological and biological age as related to physical fitness in boys 12 to 19 years

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Abstract
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 were collected in a mixed longitudinal study of Belgian school boys 19 .+-. 12 yr. 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 13-16 yr 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 yr. 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 hand). Except for static strength (arm pull), for which the explained variance ranged from 33-58%, the predictive value of body size, maturity, chronological age and their interactions is rather low, varying between 0-17%. As for body dimensions, the explained variance reaches its maximum for most motor tests at 14-15 yr.