Where do muscles get energy for exercise?

AI-generated illustration. Based on a photograph of Prof. Dr. Gürkan Özkoç; it does not depict an actual event or patient consultation.

ATP is the energy molecule muscles use directly for contraction. Because stored ATP is limited, it must be regenerated as activity continues. The body does this through more than one pathway.

Three pathways working together

The phosphocreatine system contributes to rapid ATP regeneration during very brief, intense efforts. Glycolysis supplies energy by breaking down carbohydrate. Oxidative pathways use oxygen to help produce ATP from carbohydrate and fat.

Thinking of these systems as three separate stores, one starting only after another runs out, is misleading. Their contributions overlap from the earliest moments. Exercise intensity, duration, rest intervals and training status change the proportions.

Running and strength training

Rapid energy regeneration predominates in a short sprint, while oxidative contribution is substantial during prolonged running. Still, the same fixed percentages cannot be applied to every runner and pace. Recovery between repetitions matters alongside the duration of each repetition.

Lactate production does not simply mean oxygen has run out; lactate can also fuel other tissues. This helps explain why training should not be judged solely by a burning sensation or next-day soreness.

Sources

• Gastin: Exercise energy systems (2001)
• Brooks et al.: Lactate metabolism (2022)

This article provides general information. Individual diagnosis and treatment require a clinical assessment.