Can Muscle Strength Fitness Offset The Detrimental Consequences Of Long Covid-19 Conditions On Cardiac Autonomic Function?

Objectives: Cardiac autonomic function, which is measured by heart rate variability (HRV), is a noninvasive measure of autonomic function that facilitates the identification of long COVID-19 patients at risk of developing cardiovascular complications. This study assessed differences in HRV indices along with clinical characteristics in patients with long COVID-19 conditions compared to healthy controls and examined potential moderating variables. Methods: This single-center study included long COVID-19 patients (n = 87, 71.3% women) and healthy controls (n = 71, 50.7% women). HRV was measured at R-R intervals during a 25-min supine period with a chest strap (Polar® H10 model). Four HRV indices were analyzed: SDNN, mean R-R intervals, rMSSD, and HF/LF frequency powers. Clinical characterizations such as body composition (fat mass percentage, lean mass, visceral fat, and appendicular lean mass index [ALMI]), and maximal grip strength were assessed with a dynamometer, and leg extension 1RM was assessed using EGYM Smart Strength machines. The differences between groups were investigated using ANCOVAs, and moderation analysis was assessed for the effect of long COVID-19 conditions on HRV indices and clinical characteristics. Results: The ANCOVA model reported a significant decrease in long COVID-19 conditions on HRV indices (rMSSD = 24,64 ± 2,03 vs. 35,18 ± 2,27; p = 0,002), (SDNN = 28,08 ± 1,73 vs. 35,26 ± 1,93; p = 0.012) and (R-R intervals = 885,02 ± 16,07 vs. 954,11 ± 17,99; p = 0.009) compared to controls. Moderation analysis confirmed that grip strength fully moderated the association between long COVID-19 and rMSSD. The Johnson-Neyman technique determined that the estimated grip strength point below 22.0 kg from which rMSSD has a significant effect on long COVID-19 patients (β = −7.76 [95% CI −15.3 to 0.00]; p = 0.05) after adjusting for important confounders such as age, sex, ALMI and physical activity levels. Conclusions: Our study results showed decreased parasympathetic tone in long COVID-19 conditions. The relationship between rMSSD and long COVID-19 appears to be mediated predominantly by maximal grip strength. Early diagnosis of autonomic imbalance in long COVID-19 conditions is needed to plan management and limit the progression of disease.