Skeletal muscle phosphocreatine recovery after submaximal exercise in children and young and middle-aged adults

Context: Elderly subjects have reduced mitochondrial function. However, it remains unclear whether the decline in mitochondrial function begins earlier in the life span. Objective: The objective of the study was to determine skeletal muscle mitochondrial oxidative phosphorylation by ³¹phosphorous- magnetic resonance spectroscopy (MRS) across a variety of age groups. Design: This was a cross-sectional study of 121 healthy normal-weight and overweight individuals from age 8 to 55 yr. Setting: The study was conducted at a single university medical center in Boston, MA. Participants: Participants included 68 children and 53 adults from the Boston community. Interventions and Main Outcome Measures: Phosphocreatine (PCr) recovery was evaluated by ³¹phosphorous-MRS after submaximal exercise. Subjects were also evaluated with anthropometric measurements, metabolic profiles, and measures of physical activity. Results: PCr recovery determined by ³¹phosphorous- MRS is positively associated with age in univariate analysis in a cohort of individuals aged 8-55 yr (r = +0.55, P < 0.0001). Stratification of subjects into four age groups (prepubertal and early pubertal children, pubertal and postpubertal children < 18 yr, young adults aged 18-39 yr, and middle aged adults aged 40-55 yr) demonstrates prolongation of PCr recovery with increasing age across the four groups (P < 0.0001 by ANOVA). The relationship between PCr recovery and age remains strong when controlling for gender; race; ethnicity; body mass index; measures of physical activity and inactivity; and anthropometric, nutritional, and metabolic parameters (P < 0.004). Conclusions: Skeletal muscle PCr recovery measured by ³¹phosphorous- MRS is prolonged with age, even in children and young adults.