HIIT exercise helps reshape metabolism, boost skeletal muscle

COPENHAGEN, Denmark — High-intensity interval training (HIIT) has exploded in popularity recently. Advertised as a way to attain meaningful exercise within a short timeframe, HIIT is all about brief, yet intense bursts of movement followed by even shorter periods of rest repeated cyclically. Now, new research is shedding light on just how HIIT benefits the body and your metabolism.

Researchers from the University of Copenhagen say their new findings indicate HIIT increases the amount of proteins in skeletal muscle. These proteins are absolutely essential when it comes to both muscle contraction and energy metabolism. Additionally, HIIT appears to chemically alter a different set of key metabolic proteins.

Study authors believe their work may explain why HIIT is so great for a person’s metabolism.

“Exercising has many beneficial effects that can help prevent and treat metabolic diseases, and this is likely 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,” says co-corresponding study author Morten Hostrup, Associate Professor at the Department of Nutrition, Exercise, and Sports at the University of Copenhagen, in a media release.

What is acetylation?

Acetylation is what happens when a member of the small molecule group, acetyl, combines with different molecules. Researchers say acetylation can influence the behavior of proteins.

A group of eight healthy, untrained male volunteers took part in the study. For five weeks, the group participated in high-intensity cycling training. Volunteers exercised three times weekly. The HIIT routine included: four minutes of vigorous cycling at a target rate of more than 90 percent of their maximum heart rate, followed by two minutes of rest, and then repeated four to five times per workout.

Then, via a technique called mass spectrometry, researchers observed and analyzed changes to the composition of 3,168 proteins in tissue samples collected from the participants’ thighs before the study, as well as after they had finished the training. They also examined additional changes pertaining to 1,263 lysine acetyl-sites on 464 acetylated proteins.

The analysis revealed a notable increase in the production of proteins that build mitochondria, the power plants of cells, as well as muscle contraction-related proteins. Study authors observed increased acetylation among mitochondrial proteins and enzymes involved in cellular energy production. The study also recorded fluctuations in the amount of proteins reducing the skeletal muscle’s calcium sensitivity, which is essential for muscle contractions.

The findings answer questions about muscle fatigue

Study authors explain their work confirms certain well-documented changes to skeletal muscle proteins occurring post-exercise, but also identifies new changes. For instance, the reduced calcium sensitivity may help answer why it is often harder for a muscle to contract when it is fatigued. Additionally, these findings suggest that exercise-sparked changes in protein regulation via acetylation may benefit the metabolism.

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

The study is published in eLife.

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