Heart rate response to and recovery from 6-minute walking test in post-covid syndrome individuals with and without ME/CFS symptoms

To investigate the HR response of individuals with and without ME/CFS symptoms during and immediately after the 6MWT. HR kinetics during recovery after the test were also compared between groups. 

Adults with PCS (symptoms ≥ 3 months) were assessed in person for lung function (spirometry), fatigue (Fatigue Severity Scale), and presence of ME/CFS symptoms (DePaul Symptom Questionnaire – short form). Right after, the 6MWT was conducted with participants wearing a smart shirt (Hexoskin) to monitor HR response; baseline and recovery HR values were collected one minute before and two minutes after the test, respectively, with participants seated at rest. For between-group comparisons during and after the 6MWT, absolute HR values were smoothed using a random walk algorithm and averaged at one minute. HR kinetics during recovery was analyzed by applying least-squares fitting to HR values, allowing us to extract the coefficient of determination (r²), slope, and time constant of decay (τ, tau). The distance covered in the 6MWT was normalized according to age-and sex-specific predicted values.

Twenty-seven individuals with PCS (81.5% females, age 53 ± 10 years) were assessed; ME/CFS symptoms were reported by 14 participants. No significant between-group differences were found in age, body mass index, lung function, and 6MWT distance. A MANCOVA (adjusted for baseline HR and percentage of predicted 6MWT distance) showed significantly lower HR values in individuals with ME/CFS symptoms at the 6^th minute of the 6MWT compared with those without ME/CFS symptoms (p = 0.03). Although differences in HR recovery at minutes 1 and 2 were not statistically significant between groups, individuals with ME/CFS symptoms presented a time constant two-fold higher during recovery (τ = 7.28s, slope = -0.233, r² = 0.971)  than those without ME/CFS symptoms (τ = 3.63s, slope = -0.380, r² = 0.991); slopes were also significantly different between groups after the 6MWT (p 0.001).

The results suggest an altered cardiovascular regulation with attenuated HR recovery in PCS individuals with ME/CFS symptoms compared to those without.

These findings may guide clinicians in developing targeted therapies to improve autonomic function and enhance HR recovery. Rehabilitation programs should be designed considering ME/CFS symptoms and potential cardiovascular differences. This approach can inform safer and more effective exercise interventions tailored to individual limitations, thereby minimizing the risk of symptom exacerbation in this population. Further research is needed to explore the long-term impacts of these findings on physical functioning, quality of life, and recovery trajectories of individuals with PCS.