Impact of high-intensity interval training on cardiac structure and function after COVID-19: an investigator-blinded randomized controlled trial.

A large proportion of patients suffer from a persistent reduction in cardiorespiratory fitness after recovery from COVID-19, of which the effects on the heart may potentially be reversed through the effect of high-intensity interval training (HIIT). In the present study, we hypothesized that HIIT would increase left ventricular mass (LVM) and improve functional status and health-related quality of life (HRQoL) in individuals previously hospitalized for COVID-19. In this investigator-blinded, randomized controlled trial, 12 wk of supervised HIIT (4 × 4 min, three times a week) was compared with standard care (control) in individuals recently discharged from hospital due to COVID-19. LVM was assessed by cardiac magnetic resonance imaging (cMRI, primary outcome), whereas the pulmonary diffusing capacity (DLCOc, secondary outcome) was examined by the single-breath method. Functional status and HRQoL were assessed by Post-COVID-19 functional scale (PCFS) and King's brief interstitial lung disease (KBILD) questionnaire, respectively. A total of 28 participants were included (age 57 ± 10, 9 females; HIIT: 58 ± 11, 4 females; standard care: 57 ± 9, 5 females), LVM increased in the HIIT vs. standard care group with a between-group difference of 6.8 [mean, 95%CI: 0.8; 12.8] g; P = 0.029. There were no between-group differences in DLCOc or any other lung function metric, which gradually resolved in both groups. Descriptively, PCFS suggested fewer functional limitations in the HIIT group. KBILD improved similarly in the two groups. HIIT is an efficacious exercise intervention for increasing LVM in individuals previously hospitalized for COVID-19.NEW & NOTEWORTHY In this randomized clinical trial on individuals previously hospitalized for COVID-19, a 12 wk supervised high-intensity interval training (HIIT) scheme was found to increase left ventricular mass, whereas pulmonary diffusing capacity was unaffected. The findings indicate that HIIT is an efficacious exercise intervention for targeting the heart after COVID-19.

Protective potential of high-intensity interval training on cardiac structure and function after COVID-19: protocol and statistical analysis plan for an investigator-blinded randomised controlled trial.

INTRODUCTION: COVID-19 is associated with a marked systemic inflammatory response with concomitant cardiac injury and remodelling, but it is currently unknown whether the latter is reversible. Given that high-intensity interval training (HIIT) is a powerful stimulus to improve cardiorespiratory fitness while also eliciting marked anti-inflammatory effects, it may be an important countermeasure of reducing cardiopulmonary morbidity following COVID-19. METHODS AND ANALYSIS: 40 COVID-19 survivors who have been discharged from hospital will be included in this investigator-blinded randomised study with a 12-week HIIT intervention. Patients will be 1:1 block-randomised by sex to either a supervised HIIT exercise group or standard care (control group). The main hypothesis is that a 12-week HIIT scheme is a safe way to improve loss of cardiac mass and associated cardiorespiratory fitness, despite hypothesised limited HIIT-induced changes in conventional lung function indices per se. Ultimately, we hypothesise that the HIIT scheme will reduce post-COVID-19 symptoms and improve quality of life. ETHICS AND DISSEMINATION: This study is approved by the Scientific Ethical Committee at the Capital Region of Denmark (H-20033733, including amendments 75068 and 75799) and registered at ClinicalTrials.gov (NCT04647734, pre-results). The findings will be published in a peer-reviewed journal, including cases of positive, negative and inconclusive results.Trial registration number NCT04549337.

Fidelity, tolerability and safety of acute high-intensity interval training after hospitalisation for COVID-19: a randomised cross-over trial.

OBJECTIVES: Many patients with COVID-19 suffer from persistent symptoms, many of which may potentially be reversed by high-intensity interval training (HIIT). Yet, the safety and tolerability of HIIT after COVID-19 is controversial. This study aimed to investigate the fidelity, tolerability and safety of three different HIIT protocols in individuals that had recently been hospitalised due to COVID-19. METHODS: The study was a randomised cross-over trial. We compared three supervised HIIT protocols (4×4, 6×1, 10-20-30) in 10 individuals recently discharged after hospitalisation for severe COVID-19. Each HIIT protocol had a duration of 38 min and was performed with a 1-week washout between them. Outcomes included adverse events, exercise training intensity and tolerability assessed by the Likert scale (1-10). RESULTS: All 10 participants aged 61 (mean, SD 8) years (5 males) completed all three HIIT protocols with no adverse events. High intensities were achieved in all three protocols, although they differed in terms of time spent with a heart rate ≥85% of maximum (mean (SD); 4×4: 13.7 (6.4) min; 10-20-30: 12.1 (3.8) min; 6×1: 6.1 (5.6) min; p=0.03). The three protocols were all well tolerated with similar Likert scale scores (mean (SD); 4×4: 8 (2), 10-20-30: 8 (2), 6×1: 9 (2), p=0.72). CONCLUSION: Our findings indicate that recently hospitalised individuals for severe COVID-19 may safely tolerate acute bouts of supervised HIIT as per protocol. This warrants future studies testing the potential of regular HIIT as a rehabilitation strategy in this context.