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BackgroundCardiorespiratory fitness (CRF) is essential for cardiovascular and metabolic health at any age. High levels of CRF are linked to better performance in sports and daily activities among children and adolescents. Conversely, being overweight or obese is associated with lower CRF, which can lead to decreased daily energy expenditure and reduced physical activity. This study aims to investigate CRF performance and energy expenditure in response to an exercise task among children and adolescents.MethodsThe sample consisted of 242 children and adolescents aged 8–16 years, categorized by healthy weight, overweight, obesity, and levels of cardiorespiratory fitness (low or high). Assessments included nutritional status (body mass index as Z-score), blood pressure (measured in mmHg), and electrocardiograms. Maximal oxygen consumption and ventilatory thresholds were measured using a modified Balke protocol. After initial screening, all participants performed an exercise task that involved stepping up and down on a 2-step footstool at a rate of 30 steps per minute (60 bpm) for 3 minutes.ResultsSignificant differences were observed in maximal oxygen consumption values between boys and girls across different weight categories: healthy weight (♀ 35.0 ± 5.9 ml·kg-1·min-1; ♂ 38.8 ± 6.1 ml·kg-1·min-1), overweight (♀ 32.7 ± 5.2 ml·kg-1·min-1; ♂ 35.9 ± 5.3 ml·kg-1·min-1), and obesity (♀ 27.6 ± 6.3 ml·kg-1·min-1; ♂ 32.8 ± 5.8 ml·kg-1·min-1) (p ConclusionsOur findings indicate that both overweight and obese girls and boys have lower levels of CRF. These children also engaged in exercise at a higher intensity and expended more energy, with longer recovery times for their heart rates. Furthermore, our results suggest that low CRF levels are linked to these factors.