Study associates long COVID with physical inactivity

The link between symptoms of COVID-19 and physical inactivity is increasingly evident. An article recently published in the journal Scientific Reports by researchers at the University of São Paulo (USP) in Brazil describes a study in which COVID-19 survivors with at least one persistent symptom of the disease were 57% more likely to be sedentary, and the presence of five or more post-acute sequelae of infection by SARS-CoV-2 increased the odds of physical inactivity by 138%.

“Although this was a cross-sectional study, the findings underscore the importance of discussing and encouraging physical activity at all times, including during the pandemic,” said Hamilton Roschel, last author of the study and one of the coordinators of USP’s Applied Physiology and Nutrition Research Group.

The study was one of the first to assess the effects of physical activity in the context of long COVID, usually characterized as a syndrome involving symptoms that persist for at least two months after the coronavirus infection has resolved, and that cannot be explained by other health problems.

According to a December 2020 editorial in Nature Medicine, early reports indicated that around three out of every four patients hospitalized because of COVID-19 had at least one persistent symptom six months after discharge.

In the current study, the researchers analyzed data collected by the HCFMUSP COVID-19 Study Group at Hospital das Clínicas (HC), the hospital complex run by USP’s Medical School (FM-USP). A total of 614 survivors of laboratory-confirmed COVID-19 with an average age of 56 were included in the investigation.

The patients were hospitalized between March and August 2020, and a follow-up protocol was implemented between October 2020 and April 2021 (6-11 months after discharge). They were examined and interviewed to find out how physically active they were and to assess other lifestyle items. They were also asked to report whether they had ten symptoms associated with long COVID, such as fatigue, breathlessness, severe muscle pain, taste and smell loss, and memory impairment, among others.

Participants were classified as physically inactive if they reported less than 150 minutes of at least moderately intense exercise per week, in accordance with World Health Organization (WHO) guidelines. “In our case, exercise included housework and walking, as well as sports,” Roschel said.

The more symptoms, the more sedentarism

The researchers performed a number of statistical analyses in search of correlations between symptoms of long COVID and physical inactivity.

Sixty percent of the participants were considered physically inactive, a higher proportion than those found for most regions by the Brazilian Health Ministry in a nationwide survey conducted in 2020.

Comorbidities were also significant: 37% were smokers, 58% had high blood pressure, 35% had diabetes and 17% were obese. “These are risk factors for severe COVID-19. They were expected to be frequent in the study because all the participants had been hospitalized,” Roschel said, adding that 55% had required intensive care and 37% had been intubated.

When they adjusted the results for confounding factors (variables that may affect others in a way that produces spurious or distorted associations), the researchers still found that the presence of at least one persistent symptom was associated with 57% higher odds of sedentarism. “The more symptoms, the higher the likelihood of physical inactivity,” Roschel said. When five or more symptoms were reported, the odds of physical activity rose 138%.

Certain sequelae associated with long COVID correlated very closely with physical inactivity, he added. In the adjusted statistical models, the highest correlations were with breathlessness (132%) and fatigue (101%).

“It makes sense to assume that people with this condition experience more difficulty to maintain an active routine,” he said. “But it’s also plausible that people with a sedentary lifestyle are more subject to these long-term symptoms after recovering from an acute infection. Our study doesn’t allow us to infer causality.”

Associations and hypotheses

In the article, the authors say physical inactivity “itself may be considered a persistent symptom among COVID-19 survivors.” This hypothesis has also been raised by other research groups. A Dutch paper cited in the article describes a study in which 239 recovering patients reported walking significantly less six months after the onset of symptoms than before they contracted the disease.

Roschel also believes, based on other research, that sedentarism may theoretically heighten the risk of long COVID. A study conducted in 2021 and also led by him found that hospitalized COVID-19 patients with more muscle strength and mass (hence probably less sedentary) tended to stay in hospital for less time.

In a later study, the same researchers found that patients who lost more muscle mass during hospitalization for COVID-19 were more likely to develop persistent symptoms of the disease, while also pointing to a probable correlation with higher post-acute COVID healthcare costs.

A study conducted in the United States in 2020 analyzed the prior history of physical activity for 48,440 COVID-19 patients and found the risk of hospitalization, admission to the ICU and death to be highest among those who were consistently inactive.

“Our latest study added information by describing specific correlations between physical inactivity and persistent symptoms of COVID-19. Future research should investigate this association in order to understand the underlying causes,” Roschel said.

The connection may be a two-way street in which sedentarism favors long COVID and people with long COVID tend to avoid exercise.

“From a practical standpoint, the importance of physical activity during the pandemic is clearly demonstrated,” Roschel said. There are cases in which people who have recovered from the disease should follow medical advice as to the precautions required when undertaking physical exercise, but an active lifestyle should be encouraged as a matter of public health, he stressed. Sedentarism accounts for 9% of all-cause deaths worldwide.