Metabolic responses to exercise

Exercise is associated with a complex interplay of distinct metabolic responses among children and adolescents. Using a variety of techniques and study designs, considerable progress to characterise these metabolic responses has been made over the last 90 years. Yet, measures in the paediatric literature are often bound to more stringent ethical and technical constraints than the adult literature. As such, minimally invasive respiratory gas and blood indicators of substrate and energy use have provided a platform for much of the evidence among children and adolescents, whereas insight into the underlying mechanisms at the muscle cell level remains profoundly limited and reliant on studies conducted ~40– 50 years ago. This chapter provides a critical discussion and synthesis of the available paediatric- specific literature on the metabolic responses to exercise, highlighting relevant methodological issues, gaps in knowledge, and current views. The initial focus centres on energy provision during exercise in relation to key influencing factors, particularly chronological age and puberty. Carbohydrate and fat metabolism are central to these discussions, as the contribution of protein to energy expenditure during exercise is often deemed negligible. With the acute metabolic responses to exercise having implications for cardiometabolic disease risk, the chapter culminates in a discussion of this growing evidence base in relation to postprandial glycaemia, insulinaemia, and lipaemia. Distinguishing between chronological age (referred to as ‘age’ for simplicity) and pubertal stage is a key theme throughout; where this is not essential to the interpretation of findings or findings are based on mixed samples of children and adolescents, the collective term ‘young people’ is used. Where relevant, findings from adult samples are used to provide insight into underlying mechanisms and highlight gaps in knowledge among young people.