HIIT May Help Rebuild Muscles in Polymyositis and Dermatomyositis

Brief workouts that leave you breathless may seem like exactly the wrong prescription for weakened muscles.

However, rehabilitation settings are beginning to take a different view.

For many years, people with autoimmune muscle diseases were given one consistent instruction: take things slowly, minimise strain and protect the muscles above all else. New research is now seriously questioning that cautious approach, indicating that short, high-intensity exercise sessions could improve muscle function without increasing inflammation.

When everyday movement feels like lifting concrete

Inflammatory myopathies, including polymyositis and dermatomyositis, can make routine movements feel extraordinarily difficult. People describe their legs buckling on stairs, their arms becoming exhausted while washing their hair, and persistent shortness of breath after straightforward household tasks.

These diseases develop when the immune system wrongly attacks muscle tissue, leading to ongoing inflammation. By the point at which specialists establish a diagnosis, many people have already lost around 70% of their usual endurance. Even following a year of immunosuppressive therapy, many do not recover the physical ability required for everyday life.

The cause of this restriction extends deep into individual muscle cells. Mitochondria - often called the muscle’s energy engines - become less efficient. The same amount of exertion then produces less usable energy. Conventional treatment with corticosteroids and other immune-modulating medicines can limit inflammation, but these drugs may also reduce muscle mass, weaken bones and disrupt metabolism.

For decades, clinicians worried that strenuous activity would cause further harm, much like forcing a failing engine to run at high speed. Patients were commonly advised to be cautious, avoid vigorous exertion and rely on gentle, low-resistance movements. Evidence now directly challenges that established assumption.

New data suggest that, when properly supervised, intense exercise does not fuel muscle inflammation in autoimmune disease - it may actually reverse part of the cellular energy failure.

How a Swedish trial changed views on “too intense”

Researchers at Sweden’s Karolinska Institutet recently investigated a more ambitious strategy. They enrolled 23 adults newly diagnosed with inflammatory myopathies and divided them into two groups. One completed a standard moderate home-exercise programme, while the other undertook high-intensity interval training (HIIT) three times weekly for 12 weeks.

On paper, the HIIT programme appeared demanding. Every session consisted of six maximum-effort 30-second sprints on a stationary bicycle, with two minutes of easy pedalling between each sprint. During the hard intervals, heart rate remained above 85% of the participant’s estimated maximum. The research team supervised participants carefully and tailored workloads to each person’s ability.

Changes inside and outside the muscle

At the end of three months, the gap between the groups was evident. Participants following the HIIT programme increased aerobic capacity by 16%, versus approximately 2% among those doing moderate exercise. Their endurance-test time to exhaustion increased by 23%, almost twice the improvement recorded in people following the more conventional programme.

Muscle biopsies provided further evidence. In the HIIT group, samples revealed substantial activation of mitochondrial proteins associated with energy production. These findings indicate that high-intensity exercise may have reactivated some of the inactive machinery within muscle cells.

The striking point for clinicians: performance climbed, cellular energy pathways woke up, and objective signs of inflammation did not flare.

Blood indicators of muscle damage remained unchanged. Nor did patients display clinical evidence that their disease had worsened. Although they experienced muscle soreness and tiredness, as might be expected after challenging intervals, these symptoms settled and did not cause participants to drop out.

Safety remained central

The study incorporated clear safeguards around exercise intensity. Researchers:

• medically assessed participants before placing them in the HIIT group
• monitored heart rate to ensure effort stayed within agreed boundaries
• altered bicycle resistance as fitness rose or tiredness increased
• carried out regular reviews to identify warning signs early

By approaching intensity as a carefully measured dose, rather than an imprecise instruction to “go hard”, the researchers were able to expand participants’ capacity without exposing them to unnecessary risk. This tailored method may help explain why adherence stayed high throughout the 12-week programme.

Why HIIT could matter for future treatment plans

The trial comes at an important point in the treatment of autoimmune muscle diseases. Medicines have improved survival and lowered the risk of serious complications, but many people continue to live with overwhelming fatigue and weakness. Rehabilitation often centres on lengthy, moderate-intensity sessions that can feel draining while offering little obvious improvement.

Short, strenuous sessions may alter that equation. Workouts take minutes rather than an hour, which may better suit people whose energy runs out rapidly. Better aerobic capacity and endurance could make tasks such as walking to the shops or going up a flight of stairs feel less daunting.

For some patients, high‑intensity intervals may shift the narrative from “protect and preserve” to “train and rebuild”, while still respecting the disease.

The researchers also highlight cardiovascular risk as another consideration. Chronic inflammatory conditions are associated with a greater likelihood of heart disease and stroke. When it is deemed safe for an individual, HIIT frequently improves cardiorespiratory fitness more efficiently than moderate exercise. This potential advantage may be particularly relevant for patients already managing several medicines and comorbidities.

Potential benefits at a glance

Who may benefit - and who needs caution

Despite these promising findings, this method will not be appropriate for everyone with muscle inflammation. The Swedish trial included carefully chosen adults in a controlled environment. Those with severe heart disease, advanced lung conditions or unstable autoimmune activity may encounter different risks.

Rheumatologists and neurologists advise that anyone considering this type of training should first receive a detailed assessment, including cardiac evaluation, a review of current inflammatory markers, muscle-strength testing and a clear examination of medication side effects. Personalisation must come before intervals.

A gradual route may be more suitable for some people. Someone could begin with gentle walking or cycling, then introduce a small number of moderately harder intervals before progressing towards something more like HIIT if their body copes well. The idea of “relative” intensity is important: an effort that is hard for a recently diagnosed patient is entirely different from one that challenges a fit cyclist.

Rethinking “rest versus movement”

The research also prompts a wider question about managing chronic illness. Similar concerns about exertion arise in conditions ranging from rheumatoid arthritis to long-term cancer treatment. Patients may come to see a raised heart rate or burning muscles as warning signs, especially where activity has previously been followed by a flare-up.

Carefully supervised exercise can help people regain confidence in their bodies. When they see measurable improvement without their symptoms escalating, their connection with movement can begin to change. That psychological benefit may be as meaningful as any laboratory measurement.

At the same time, healthcare professionals should avoid presenting HIIT as a universal recommendation. The evidence base is still small, and most studies have been conducted in specialist centres. Beyond those settings, reduced supervision, different equipment and less follow-up may leave a narrower margin for safety.

What this means for patients now

For someone with polymyositis or dermatomyositis, this is not an invitation to begin sprint intervals at the local gym immediately. The message is more nuanced: the previous belief that “intense exercise equals harm” no longer carries the same certainty. With expert support, intensity may become a useful tool instead of a danger.

A sensible route could involve three stages: ask your specialist whether supervised higher-intensity exercise may be appropriate; seek a referral to a physiotherapist or exercise physiologist experienced in inflammatory myopathies; and begin with a trial period during which symptoms and blood tests are closely monitored.

Researchers are now examining longer-term issues. Can HIIT sustain its benefits for a year or longer? Might it make lower steroid doses possible? Could it postpone disability or lessen the need for mobility aids? The answers will determine whether this approach remains specialised or becomes part of standard care pathways.

Greater understanding of mitochondrial function in autoimmune muscle disease could also reveal new medicine targets. The same proteins that become active in biopsies after intense exercise may help inform treatments designed to restore energy production more directly. In this way, what occurs on a laboratory bicycle could shape future medicines for people whose muscles currently fail them much too soon.