Relationship between physical activity, body fatness and cardiorespiratory fitness in South African adolescents: The PAHL Study

Low cardiorespiratory fitness and inactivity are strong health predictors associated with excessive fatness. The objective of this study was to determine the associations between physical activity (PA) and cardiorespiratory fitness and body fatness in South African adolescents. A cross-sectional study was performed with a subsample of 149 school-going adolescents (58 boys and 91 girls) with a mean age of 15.7 ± 0.8 years whom were participating in the Physical Activity and Health Longitudinal Study (PAHLS). Body mass, height, and skinfolds were assessed according to the standards of the International Society for the Advancement of Kinanthropometry (ISAK). Subsequently, body mass index (BMI) and percentage of body fat (%BF) were calculated. Cardiorespiratory fitness was derived from predicted VO2max, and PA assessed by combined heart rate and accelerometry (ActiHeart®, CamNTech). Physical activity was classified according to activity categories. Out of 149 participants, 100 (67.1%) had normal body mass; 26 (17.5%) were underweight and 23 (15.4%) were overweight. Seventeen (18.7%) girls and six (10%) boys were overweight or obese. The prevalence of underweight in boys was 29.3% and 9.9% in girls. A total of 102 (68.5%) participants were sedentary and 47 (31.5%) were active. The overweight group was significantly (p<0.05) heavier and fatter than the underweight and the normal groups. The lowest performance for predicted VO2max was found in the overweight adolescents. A significant positive relationship was found between BMI and PA in girls (ß=0.01 [95%CI: 0.007; 0.019]). A significant negative associations (p<0.05) was found between BMI and VO2max, (Boys; ß= -0.31 [95%CI: -0.50; -0.19]; Girls; ß= -0.17 [95%CI: -0.33; -0.02]). In conclusion, overweight adolescents were mainly sedentary and performed poorly in cardiorespiratory fitness compared to their underweight peers. Low cardiorespiratory fitness performance was negatively associated with relatively high fatness. School-based PA programmes are needed to reduce relatively high body fatness and improve cardiorespiratory fitness in adolescents