Eccentric Training in Pulmonary Rehabilitation of Post-COVID-19 Patients: An Alternative for Improving the Functional Capacity, Inflammation, and Oxidative Stress

SIMPLE SUMMARY: Exercise is the cornerstone of pulmonary rehabilitation (PR) programs. Although all exercise has concentric (CONC, where the muscle groups shorten to produce force) and eccentric (ECC, characterized by lengthening muscle during its muscle contraction) contractions or components, usually PR is focus on CONC as the main training modality. Data show that this exercise modality increases cardiopulmonary stress, eliciting higher ventilation and consequently exacerbating dyspnoea, been more stressful for patients with chronic respiratory diseases (e.g., COPD and interstitial lung diseases). Similarly, higher cardiopulmonary stress has been associated with more oxidative stress. This aspect has been proposed as the central pathophysiological mechanism involved in the functional limitation of post-COVID-19 patients with moderate-to-severe damage associated with SARS-CoV-2 infection and prolonged hospital stay. Thus, traditional PR programs with CONC as a primary exercise modality can exacerbate dyspnoea and leg fatigue in these patients, repercussing in early exercise intolerance and diminishing the adherence to PR. On the other hand, ECC training has increased the locomotor muscle mass without significant cardiopulmonary stress, improving functional capacity and self-autonomy. This review discusses the mechanism that supports aerobic ECC exercise as a novel alternative to conventional CONC exercise included in traditional PR for post-COVID-19 patients. ABSTRACT: The purpose of this narrative review is to highlight the oxidative stress induced in COVID-19 patients (SARS-CoV-2 infection), describe longstanding functional impairments, and provide the pathophysiologic rationale that supports aerobic eccentric (ECC) exercise as a novel alternative to conventional concentric (CONC) exercise for post-COVID-19 patients. Patients who recovered from moderate-to-severe COVID-19 respiratory distress demonstrate long–term functional impairment. During the acute phase, SARS-CoV-2 induces the generation of reactive oxygen species that can be amplified to a “cytokine storm”. The resultant inflammatory and oxidative stress process causes organ damage, particularly in the respiratory system, with the lungs as the tissues most susceptible to injury. The acute illness often requires a long-term hospital stay and consequent sarcopenia. Upon discharge, muscle weakness compounded by limited lung and cardiac function is often accompanied by dyspnea, myalgia, anxiety, depression, and sleep disturbance. Consequently, these patients could benefit from pulmonary rehabilitation (PR), with exercise as a critical intervention (including sessions of strength and endurance or aerobic exercises). Unfortunately, conventional CONC exercises induce significant cardiopulmonary stress and increase inflammatory and oxidative stress (OS) when performed at moderate/high intensity, which can exacerbate debilitating dyspnoea and muscle fatigue post-COVID-19. Eccentric training (ECC) is a well–tolerated alternative that improves muscle mass while mitigating cardiopulmonary stress in patients with COPD and other chronic diseases. Similar benefits could be realized in post-COVID-19 patients. Consequently, these patients could benefit from PR with exercise as a critical intervention.