Moderate-Intensity Cycling Training Combined With Intereffort Recovery Hypoxia for Lung Rehabilitation After COVID-19: A Double-Blinded, Randomized Controlled Trial

Background: Physiological adaptations associated with chronic exposure to hypoxia have been suggested as potential factors contributing to reduced COVID-19 severity in high-altitude populations. Therefore, hypoxic exercise training has emerged as a potential strategy to enhance recovery following COVID-19 infection. Hypothesis: Moderate-intensity training associated with continuous hypoxia (HYP) or intereffort recovery hypoxia (IEH) could induce additional stimulus to cardiorespiratory capacity in COVID-19 rehabilitation. Study Design: Randomized controlled clinical trial. Level of Evidence: Level 2. Methods: Sixty-one adults recovered from COVID-19 (35.9 days after diagnosis, on average) were randomly assigned to a no-exercise control group (CON, n = 18) or moderate-intensity training groups under normoxia [NOR, n = 12; fraction of inspired oxygen (FiO 2 ) = 20.9%], HYP (n = 16; FiO 2 = 13.5%), or IEH (n = 15; efforts at 20.9% and the recovery periods at 13.5%). Ventilatory and lactate thresholds (VT and LT, respectively), peak power output (PPO) determined during a graded exercise cycling test to exhaustion, forced expiratory volume in 1 second (FEV1), and forced vital capacity (FVC) were accessed before and after an 8-week cycling training program (3-6 efforts of 5 min at 90% to 110% of LT interspersed with 2.5 min of recovery, 3 times per week). Group × time effects were assessed using generalized mixed-effects models. Results: VT increased in all groups (all P ≤ 0.013), with no group × time interaction (all P > 0.15). VT ventilation increased only in the training groups (all P ≤ 0.013), and there was a group × time effect for IEH versus CON ( P = 0.036). PPO increased only in the training groups ( P < 0.001), with group × time interactions for all training groups versus CON (all P ≤ 0.002). Maximal ventilation increased in NOR ( P = 0.016) and HYP ( P = 0.012), both differing from CON ( P = 0.005). FEV1 decreased in NOR only ( P < 0.001), with group × time interactions versus HYP ( P < 0.001) and IEH ( P = 0.035). Conclusion: Moderate-intensity training promoted benefits in the indicators of aerobic capacity and PPO of COVID-19 convalescents. The additional exposure to hypoxia in the training sessions did not result in differences compared with NOR. Clinical Relevance: This training protocol can be used in COVID-19 rehabilitation. In addition, HYP and IEH can achieve similar results compared to NOR, with probably lower intensity.