Unraveling the Mechanisms Behind Exercise Intolerance and Recovery in Long COVID

Patients suffering from long COVID may exhibit autonomic dysregulation. However, the association between autonomic dysregulation and exercise intolerance and the impact of therapeutic interventions on its modulation remains unclear. This study investigated the relationship between heart rate recovery at the first minute (HRR1), a proxy for autonomic imbalance, and exercise intolerance in patients with long COVID. Additionally, the study aimed to assess the effects of a 12-week home-based inspiratory muscle training program on autonomic modulation in this patient population. This study is a post hoc subanalysis of a randomized trial in which 26 patients with long COVID were randomly assigned to receive either a 12-week inspiratory muscle training program or usual care alone (NCT05279430). The data were analyzed using Pearson's correlation and linear mixed regression analysis. The mean age was 50.4 ± 12.2 years, and 11 (42.3%) were women. Baseline HRR1 was significantly correlated with maximal functional capacity (peakVO2) (r = 0.402, P = .041). Patients with lower baseline HRR1 (≤22 bpm) exhibited higher resting heart rates and lower peakVO2. Inspiratory muscle training led to a more substantial increase in peakVO2 in patients with lower HRR1 at baseline (P = .019). Additionally, a significant improvement in HRR1 was observed in the IMT group compared to the usual care group after 12-week (Δ +9.39, 95% CI = 2.4-16.4, P = .010). Lower baseline HRR1 is associated with exercise intolerance in long COVID patients and may serve as a valuable criterion for identifying individuals likely to benefit more from a home-based inspiratory muscle training program.