The study – carried out using a sample of men – suggests that HIIT workouts boost the amount of proteins in skeletal muscle that are essential for energy metabolism and muscle contraction, while also chemically altering key metabolic proteins.

“Exercising has many beneficial effects that can help prevent and treat metabolic diseases,” says Morten Hostrup, first and co-corresponding author and associate professor at the Department of Nutrition, Exercise, and Sports at the University of Copenhagen. “This is likely to be the result of changes in energy use by skeletal muscles.

“We wanted to understand how exercise alters the muscles’ protein content and how it regulates the activity of these proteins through a chemical reaction called acetylation.”

These results may explain the beneficial effects of HIIT on metabolism, and pave the way for additional studies exploring how exercise impacts these processes.

The study involved eight healthy, untrained male volunteers who completed five weeks of high-intensity cycling training, working out three times per week, finishing four minutes of cycling at a target rate of more than 90 per cent of their maximum heart rate, followed by a two-minute rest. They repeated this pattern four to five times per workout.

Using mass spectrometry, the team analysed changes to the composition of 3,168 proteins in tissue samples collected from the participants’ thighs, before the study and after they completed the training. They also examined changes relating to 1,263 lysine acetyl-sites on 464 acetylated proteins.

Their analyses showed an increase in the production of proteins used to build mitochondria, which produce energy in cells, and in proteins related to muscle contractions, as well as changes in the amount of proteins that reduce the skeletal muscle’s calcium sensitivity, which is essential for muscle contractions.

“This provides new information about how skeletal muscle adapts to exercise, including the identification of novel exercise-regulated proteins and acetyl-sites,” says co-corresponding author Atul Deshmukh, of the Novo Nordisk Foundation Center for Basic Metabolic Research at the University of Copenhagen. “We hope our work will stimulate further research into how exercise helps improve metabolic health in humans.”