RESUMO
Age, gender, body composition and genetic background affect cardio respiratory fitness. In children, the variability of physiological responses to exercise yield different interpretations of the effective parameters. The aim of the present study was to investigate the effect of age, gender, body composition on cardio respiratory fitness of students of Semnan city aged 8-11 years, using the FFMI-FMI regression model. This cross-sectional study was performed on 685 students [347 boys and 338 girls]. Subjects were selected via a multi-level cluster sampling. After adjustment for differences in age, gender and body mass using the FFMI-FMI regression model, i.e. Fat free mass index [FFMI], [dividing fat free mass to squared stature] was predicted by fat mass index [FMI] [dividing fat mass to squared stature] subjects were categorized into 3 groups: The Normal, the Solid [higher than normal FFM group] and the Slender [lower than normal FFM group]. The 20 m Shuttle run test used to estimate maximal oxygen uptake [VO[2] max] as an index of cardio respiratory fitness, expressed in absolute values. There was a positive significant association between age and VO[2] max [P<0.05]. The solid group had higher values, while the slender group had lower values in VO[2]max. Boys had better cardio respiratory fitness than girls in. There are significant direct positive associations between age and body composition and VO[2] max