Exercise and ageing impact the kynurenine/tryptophan pathway and acylcarnitine metabolite pools in skeletal muscle of older adults.
Level 3 - non-randomized controlled study
Non-randomized comparative physiological study across age and activity cohorts with acute exercise intervention
PubMed 36814134 · doi:10.1113/JP284142
What was done
Investigators evaluated resting and exercise-induced skeletal muscle metabolomic responses in three cohorts: active older adults, sedentary older adults, and active young adults. Percutaneous vastus lateralis biopsies were obtained before, immediately after, and 3 hours following a bout of endurance cycling. Muscle metabolome profiling was performed using tandem mass spectrometry, mitochondrial energetics were measured via high-resolution respirometry in permeabilized fiber bundles, and fiber type distribution was assessed by immunohistology.
What was found
Metabolites of the kynurenine/tryptophan pathway varied by age and physical activity: kynurenine was elevated in older muscle, while downstream metabolites (kynurenic acid and NAD+) were higher in active adults and correlated with cardiorespiratory fitness and muscle oxidative capacity. Acylcarnitines were elevated in muscle from physically active participants across age groups. Despite baseline differences, acute exercise-induced changes in whole-body substrate utilization, muscle acylcarnitines, and ketone bodies were similar across all groups. The abstract reports no numerical values, effect sizes, or p-values.
Why it matters
This study shows that physical activity influences human skeletal muscle tryptophan metabolism toward NAD+ synthesis and that older muscle retains the acute metabolic responsiveness to endurance exercise observed in younger adults.
Limits
The abstract does not state the sample size (n), participant sex, cycling intensity/duration, or exact numerical results. Cross-sectional group comparisons limit causal conclusions regarding chronic training effects versus baseline phenotypic confounding.
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- supports Marathon runners have resting NAD levels roughly 50% higher than untrained individuals.