Does skeletal muscle carnitine availability influence fuel selection during exercise?
Level 5 - mechanism / opinion, no new human data
Narrative review synthesizing mechanistic theory without new empirical data or systematic methodology.
PubMed 29037265 · doi:10.1017/S0029665117003937
What was done
This narrative review synthesizes literature regarding skeletal muscle fuel selection during exercise. It examines the hypothesis that high carbohydrate flux reduces the availability of muscle carnitine to carnitine palmitoyltransferase 1 (CPT1), thereby limiting mitochondrial fat transport during high-intensity exercise, integrating findings from studies on in vivo nutritional elevation of muscle carnitine.
What was found
The abstract notes that fat and carbohydrate oxidation both increase up to 60-70% of maximal oxygen consumption, beyond which carbohydrate use accelerates and fat oxidation declines relatively and absolutely. No specific statistical metrics or effect sizes are reported in the abstract.
Why it matters
Clarifying the role of muscle carnitine availability in substrate metabolism helps explain the physiological limits of fat oxidation during strenuous exercise and evaluates the rationale for carnitine supplementation.
Limits
This is a narrative review discussing mechanistic pathways rather than an empirical trial or systematic review. The abstract reports no empirical sample sizes or quantitative outcome data.
Cited by
- supports Increasing lipolysis and plasma fatty acid availability through supplementation does not necessarily increase fat oxidation because muscle CPT limits oxidation.