Peripheral muscle fatigue was the most common cause of exercise limitation in patients recovered from COVID-19 regardless of disease severity, in a study of nearly 300 individuals.
The source and magnitude of exercise intolerance in post–COVID-19 patients has not been well studied, said Mauricio Milani, MD, of Fitcordis Exercise Medicine Clinic, Brasilia, Brazil, in a presentation at the annual congress of the European Association of Preventive Cardiology.
To assess exercise intolerance, the researchers performed cardiopulmonary exercise testing (CPET) on 144 adults who had recovered from COVID-19 and 144 matched controls who had not had COVID-19. The average age of the participants was 43 years, and 57% were male. COVID-19 was defined as mild, moderate, or severe in 60%, 21%, and 19% of the cases, respectively.
Residual symptoms were present in 41% of cases. CPET was performed at roughly 14 weeks after disease onset.
Among the COVID-19 patients, most of the CPET limitations (92%) were caused by muscle fatigue; cardiovascular limitations were noted in 2%, and pulmonary limitations were noted in 6%.
Data from the post-COVID CPET showed differences in peak oxygen consumption, as well as the first and second ventilatory thresholds (VT1 and VT2) between COVID-19 patients and controls, and with lower values related to higher illness severities, Dr. Milani said. Heart rate also varied according to illness severity, with lower values significantly related to higher illness severities and significant differences between COVID patients and controls.
A total of 42 individuals with COVID-19 had previous CPET data for comparison (27 with mild disease and 15 with moderate or severe disease), Dr. Milani said. In the subgroup with mild disease, the only significant difference in CPET results before and after COVID-19 was peak speed. In the moderate/severe group, the researchers observed higher reductions in peak speed and also reductions in oxygen consumption at peak and thresholds.
However, peak oxygen flows were not different before and after COVID-19 in either the mild or moderate/severe subgroups, Dr. Milani said.
The study findings were limited in part by the relatively small study population; however, the results indicate that peripheral muscle fatigue is the primary etiology in exercise limitation in post–COVID-19 patients.
“Our data suggest that treatment should emphasize comprehensive rehabilitation programs, including aerobic and muscle strengthening components,” Dr. Milani concluded.
COVID challenges remain unclear
“After COVID, patients often display a postviral syndrome with a wide range of symptoms,” Matthew Martinez, MD, a sports cardiologist at the Atlantic Health System in Morristown, N.J., in an interview said. “These conditions frequently lead to a sense of tiredness and weakness, pain, difficulty concentrating, and headaches that linger after the viral infection has cleared,” and these symptoms may continue for weeks.
However, this scenario is not unique to COVID-19: “This study confirms the importance of muscle fatigue in recovery,” said Dr. Martinez. “Recovery from viral illness requires hydration, sleep and slow progression return to exercise.” Consequently, Dr. Martinez said he was not surprised by the current study findings.
The take-home message for clinicians is to be aware that COVID-19 can have postviral syndrome, as is common after other infections, Dr. Martinez noted. The findings provide a starting point for discussing concerns with patients and explaining that a slow return to normal with usual care is expected. “Time to recovery will vary by individual,” he said. “Additional research is needed to identify which specific therapies are most important to help reduce time to recovery, and what new therapies could be developed to help facilitate muscle fatigue recovery and reduce time needed to recover.”
The study was supported by CAPES and CNPq. Dr. Milani had no financial conflicts to disclose. Dr. Martinez had no financial conflicts to disclose.