Dynamic Acylcarnitine Responses to Exercise and Recovery in Aging Skeletal Muscle: Evidence, Interpretation, and a Validation Framework

Dynamic acylcarnitine profiling could reveal how aging muscle handles an energetic challenge, but concentration changes are often interpreted without separating adaptive buffering from impaired oxidation. This narrative review integrates human exercise, aging, intervention, mechanistic, and analytical evidence to define what exercise–recovery trajectories can establish. Three distinctions emerge: blood concentration is not muscle flux; acetyl buffering is not equivalent to incomplete fatty-acid oxidation; and oxidation capacity, metabolic flexibility, and functional recovery require different validation outcomes. A muscle study involving 44 young and older adults found broadly conserved acute responses despite differences in resting pools and activity. A 25-week intervention in 14 older men increased muscle carnitine and exercise fat oxidation by approximately 20% without improving insulin-stimulated glucose disposal. These findings challenge a uniform interpretation of altered acylcarnitines as an aging defect. The review connects molecular annotation, specimen choice, workload, feeding, and sampling time to response features and bioenergetic or functional outcomes. Its contribution is a validation framework for distinguishing physiological adaptation from persistent metabolic mismatch and testing whether dynamic measurements add information beyond resting profiles. Direct older-adult recovery studies remain limited. Repeatability, tissue or flux comparison, and external validation are required before diagnostic thresholds or individualized prescriptions can be justified.