Long COVID is a condition that affects many people who have had COVID-19, causing persistent and debilitating symptoms such as fatigue, shortness of breath, muscle aches and loss of smell. One of the most challenging aspects of long COVID is the worsening of symptoms after physical activity, known as post-exertional malaise (PEM). A new study published in Nature Communications has shed some light on the possible mechanism behind PEM in long COVID.
Muscle structure and function
The researchers from the Amsterdam University Medical Center analysed muscle biopsies and blood samples from 25 people with long COVID and 21 people who had recovered from COVID-19 without long-term effects. They compared the muscle structure and function of both groups before and after a controlled cycling test.
They found that people with long COVID had a higher proportion of fast-twitch glycolytic muscle fibres, which are more prone to fatigue because they have fewer mitochondria, the organelles that produce energy for the cells. They also found that the mitochondria in long COVID patients were smaller and less efficient than those in healthy participants, resulting in lower oxygen uptake and energy production.
The researchers also detected signs of inflammation and oxidative stress in the muscles of long COVID patients, which could further impair mitochondrial function and damage muscle cells. They suggested that these changes could be due to a dysregulated immune response triggered by the viral infection.
Implications and recommendations
The study provides new insights into the link between muscle energy loss and long COVID, and suggests that PEM is not caused by blood clots or hypoxia, as previously thought. It also highlights the importance of avoiding intense exercise for people with long COVID, as it could worsen their symptoms and cause further damage to their muscles.
The researchers recommended that people with long COVID should follow a gradual and personalised exercise program, under the guidance of a specialist, to improve their muscle function and quality of life. They also called for more research to understand the underlying causes of long COVID and to develop effective treatments.