OBJECTIVE:To study the effect of physical activity on whole body fat (BF), its regional deposition and the influence of body fatness on physical performance in prepubertal children. DESSIGN: Cross-sectional study. SUBJECTS: A total of 114 boys (9.471.5 y, Tanner I-II), randomly sampled from the population of Gran Canaria (Spain), 63 of them physically active (PA, at least 3 h per week during the previous year) and 51 nonphysically active (non-PA). MEASUREMENTS: Body composition (DXA), anthropometric variables (body circumferences and skinfolds) and physical fitness were determined in all subjects. RESULTS: The PA obtained better results in maximal oxygen uptake, isometric leg extension force, vertical jump (muscular power), and 300 m (anaerobic capacity) and 30 m running tests (speed) than the non-PA. A lower percentage of body fat (% BF) (4 U less, Po0.05), whole BF mass (36% less, Po0.05) and regional fat mass (28, 25, and 30% less in the trunk, legs and arms, respectively, all Po0.05) was observed in the PA compared to the non-PA. The waist and hip circumferences correlated more closely with both the fat mass accumulated in the trunk region and the % BF (r ¼ 0.81-0.95, Po0.001) than the waist-to-hip ratio (WHR). The WHR correlated with the percentage of the whole fat mass accumulated in the trunk (PFT) (r ¼ 0.52-0.53, Po0.001). In both groups, the PFT increased curvilinearly with the % BF, regardless of the level of physical activity. ANCOVA analysis revealed that total and regional fat masses explained less than 40% of the difference in performance between the PA and non-PA group. The mean speed in the 30 m running test (V 30 ), combined with the height and whole body mass, has predictive value for the BF mass (R ¼ 0.98, Po0.001). The % BF may be estimated from the body mass index (BMI) and V 30 (% BF ¼ 8.09 þ 2.44 Á BMI (kg m À2 )-5.8 Á V 30 (m s À1 ), R ¼ 0.94, Po0.001) in prepubertal boys. CONCLUSIONS: Regular participation in at least 3 h per week of sports activities and competitions on top of the compulsory physical education program is associated with increased physical fitness, lower whole body and trunkal fat mass in prepubertal boys.

Objective: To analyse the effect of extracurricular physical activities on fat mass accumulation and physical fitness during growth in early pubertal males. Design: Longitudinal study. Subjects: A total of 42 male children (9.471.4 years, Tanner I-II and 12.771.5 years, Tanner III-IV, before and after the 3.3 years follow-up, respectively), randomly sampled from the population of Gran Canaria (Spain), 26 of them physically active (PA, at least 3 h per week during 3 years) and 16 non-physically active (non-PA). Measurements: Body composition (dual-energy X-ray absorptiometry), anthropometrics (body circumferences and skinfolds) and physical fitness variables (dynamic and isometric force, anaerobic capacity and maximal aerobic power) were determined in all subjects. Results: Both groups had comparable body sizes at the start and the end of the study. Body mass index increased with growth more in the PA than in the non-PA group (Po0.05). However, fat mass accumulation with growth was lower in the PA than in the non-PA (Po0.05). There was a positive relationship between the increment of total and trunkal fat mass, especially in nonactive children (r 2 ¼ 0.93). In contrast, there was an inverse relationship between the total lean mass growth and the accumulation of total and regional fat mass (r ¼ À0.37 to À0.41, all Po0.05). Physical fitness was maintained in the PA, while it worsened in the non-PA children. Conclusions: Without any dietary intervention, children who regularly participate in at least 3 h per week of sports activities are more protected against total and regional fat mass accumulation. They also increase their total lean and bone mass to a greater extent than children who do not participate in extracurricular sport activities. In addition, PA children maintain their physical fitness during growth, while it deteriorates in the non-PA children.

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