Muscles can swell in size as a weird new side effect of COVID-19

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HASSELT, Belgium – ( – COVID-19 could cause a person’s muscles to swell, according to a new study of critically ill patients. Belgian researchers have found that some people with a severe case of the virus saw their muscle fibers swell by more than 60% while in hospital.

Scientists believe that the body’s immune response damages mitochondria, the powerhouses of cells, leading to loss of energy that accumulates water, causing muscles to swell. The phenomenon stunned the Belgian team, as muscle twitching is a common complication in people spending several days in an intensive care unit.

Biopsies of the strongest muscle in the thigh of 18 COVID patients revealed that the muscles of four of them grew “massively” during their stay in intensive care. Type 1 and type 2 fibers in these patients increased by 62 and 32 percent, respectively.

The researchers explain that type 1 muscle fibers support endurance activities, while type 2 fibers handle fast and powerful moments.

Lead author Dr. Toon Mostien of Jessa Hospital notes that this type of swelling can ultimately lead to the death of muscle fibers. Since it’s normal for muscles to shrink due to inactivity, the team believes this strange side effect is a temporary condition.

Overall, type 1 fiber increased by 6% and type 2 fiber decreased by 5% across all COVID patients in the study. The team considers this change to be statistically insignificant.

COVID also causes severe muscle shrinkage

However, when the study authors excluded patients with severe swelling from the results, the remaining patients showed significant muscle shrinkage. In patients without COVID swelling, their type 1 muscle fibers shrank by 11% and their type 2 muscles shrunk by 17%.

The average age of these participants was 69 and the majority were male. The team scanned samples under a microscope to detect any changes that occurred during the first week of intensive care. Typically, bed rest and mechanical ventilation often lead to muscle wasting. It can hinder recovery and affect mobility and quality of life.

Previous research has found that the fibers shrink by almost a fifth after a week in intensive care. The team fears COVID could cause even greater damage. Mostien’s team found that the number of capillaries supplying type 1 and type 2 fibers with oxygen and nutrients decreased by 5 and 10 percent, respectively.

“Although the results were not significant, a drop in perfusion of almost 10% could potentially contribute to the destruction of muscle fibers,” explains Dr. Mostien in a press release.

“There are concerns that the immune response to Covid may exacerbate muscle wasting, meaning that critically ill Covid patients experience more severe muscle damage than the general ICU population,” concludes the study author. “Given the global burden of COVID-19, it is essential that we learn more about it and our research is an important first step.”

The researchers presented their findings at Euroanaesthesia 2021, a virtual meeting of the European Society for Anaesthesiology and Intensive Care.

South West News Service writer Mark Waghorn contributed to this report.