High-intensity interval training boosts fitness and muscle endurance more effectively than traditional home exercise programmes in people recently diagnosed with inflammatory muscle disease. That is the conclusion of a new study from Karolinska Institutet, published in eBioMedicine.

Idiopathic inflammatory myopathies (IIM) are a group of rare autoimmune diseases that cause muscle weakness and fatigue. Standard treatment usually combines medication with light to moderate home exercise. However, the impact on aerobic fitness has been limited. Researchers at Karolinska Institutet have now investigated whether high-intensity interval training (HIIT) could deliver better results.

The study involved 23 patients who had recently developed IIM. Participants were recruited from Karolinska University Hospital in Stockholm and Uppsala University Hospital, Sweden. They were randomly assigned to two groups: one trained HIIT on a stationary bike three times a week for twelve weeks, while the other followed a moderate-intensity home exercise programme. The researchers assessed aerobic capacity, muscle endurance and markers of disease activity before and after the training period.

Clear improvements with HIIT

Results showed that the HIIT group improved their aerobic capacity by an average of 16 percent, compared with 1.8 percent in the home exercise group. Muscle endurance also increased more with HIIT, and muscle samples revealed signs of enhanced mitochondrial function, which is crucial for the cells’ energy production. At the same time, disease activity remained stable in both groups, suggesting that intensive training is safe. There were no signs that exercise increased inflammation or muscle damage.

“Common symptoms of IIM include muscle weakness and reduced endurance. Our study shows that high-intensity interval training is safe and markedly improves muscle function and aerobic capacity. Better fitness can lower the risk of cardiovascular disease, while patients gain more stamina and independence. This could become an important complement to medication in improving physical capacity and quality of life,” says Kristofer Andreasson, researcher at the Department of Medicine, Solna, Karolinska Institutet.

The researchers emphasise that the study is small and that further studies are needed to confirm the findings and assess long-term effects.

The study was mainly funded by the Swedish Research Council, Region Stockholm (ALF), the Swedish Rheumatism Association, King Gustaf V’s 80-Year Fund (Stiftelsen Konung Gustaf V:s 80-årsfond), and the Swedish Heart Lung Foundation. Information on potential conflicts of interest is available in the scientific article.