Abstract
BACKGROUND: Physiological responses to exercise differ between children and adults, but achieving maximal exertion in children complicates the interpretation of VO(2)(max). This study, therefore, examines age- and sex-related physiological differences in submaximal parameters during incremental exercise. METHODS: In this cross-sectional study, 24 children (7-11 years), 20 moderately trained adults (MTA), and 20 well-trained adults (WTA; 20-30 years) completed a maximal incremental exercise test on a cycle ergometer with continuous respiratory measurement. Linear regression models analysed age and sex differences in ventilatory thresholds (VT1, VT2) and oxygen uptake efficiency slope and plateau (OUES), with Cohen's d effect sizes reported. RESULTS: Children showed higher body mass-adjusted VO(2) at VT1 and VT2 (d = 0.58-0.66) compared to MTA, and slightly lower VT2 values than WTA (d = 0.35). Adults had higher absolute OUES (d = 0.37-1.45) and OUEP (d = 0.60-0.81), while children exhibited higher body mass-adjusted OUES (d = 0.87 - 1.80). Males had higher VO(2) at VT2, OUES, and OUEP (d = 0.41-0.81), while females showed higher relative VO(2) at VT1 and VT2 (d = 0.44-0.59) compared to males. CONCLUSIONS: Children rely more on oxidative metabolism than adults. Maturation influences exercise efficiency more than body mass, underscoring physiological differences. These age- and sex-specific patterns call for longitudinal studies to further explore the roles of growth and training. IMPACT: This study identifies clear physiological differences in submaximal CPET parameters between children and adults. It adds novel insight by including both ventilatory thresholds and oxygen uptake efficiency, adjusted for body mass and training status. The findings suggest children rely more on oxidative metabolism, emphasizing the importance of maturation on exercise efficiency and informing age- and sex-specific assessment protocols in pediatric exercise physiology.