Timing and intensity matter when exercising, according to new study

Researchers at University of Galway have revealed how careful consideration of the timing and intensity of training will benefit muscle health. The study examined if a bout of brief supramaximal acute exercise had superior effects on muscle physiology and metabolic health than a longer bout of continuous acute exercise.

The randomised cross-over study included 12 healthy young active men, who completed single acute bouts of either sprint interval exercise or moderate-intensity continuous exercise – or a non-exercise control session. In order to fully assess the metabolic impacts, the researchers measured acute changes in skeletal muscle insulin sensitivity. Muscle biopsies were also performed pre and post the interventions to quantify changes in muscle glycogen content and insulin signalling proteins. 

A single session of sprint interval exercise was found to produce greater improvements in whole-body and skeletal muscle insulin sensitivity than a longer bout of moderate intensity continuous exercise, despite requiring significantly less time and total work. The findings suggest that exercise intensity is a more important driver of rapid metabolic adaptations than exercise duration, highlighting sprint interval exercise as a time-efficient strategy for improving insulin sensitivity.

Dr Enda Murphy, an exercise scientist working at CÚRAM – the Research Ireland Centre for Medical Devices based at University of Galway – led the international collaboration with scientists from Dublin City University and Toulouse University in France.

He said: “The findings were interesting and unexpected. There were much bigger improvements in muscle function after the short, intensive exercise bouts compared to the longer bout of less intensive exercise, even though the overall workload with the short intensive bout was much lower. Our analysis also showed improvements in insulin sensitivity – which relates to how effectively the body’s cells respond to insulin in order to absorb glucose from the bloodstream and regulate blood sugar levels.”

Dr Cedric Moro, part of the research team based in the Institute of Metabolic and Cardiovascular Diseases, Toulouse University, France, said: “Whether the findings apply to other groups such as women, older people, or those with chronic medical conditions like obesity, needs further study.

“However, the fact that we were able to quantify very precisely the changes in insulin sensitivity, as well as the changes in muscle at a molecular and microscopic level, with the biopsy samples makes us confident that what we are seeing is real.”

Reference
Murphy E, Laurens C, Frances L, et al. Acute metabolic and molecular responses to sprint interval versus moderate intensity continuous exercise in healthy young men. Am J Physiol Endocrinol Metab. 2026;330(5):E562-E571. doi:10.1152/ajpendo.00548.2025.

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