The largest prospective cardiac follow-up of athletes after mild COVID-19 has reported its 12-month outcomes, and the headline finding will be welcomed by team doctors and recreational endurance runners alike: cardiac structure, myocardial deformation and cardiopulmonary performance remained stable across the cohort, with no evidence of adverse left or right ventricular remodelling. The COSMO study (Cardiac Outcomes Sport in Mild Outpatients) was published in Frontiers in Cardiovascular Medicine on 29 April and pulls together 312 athletes from elite, sub-elite and recreational endurance backgrounds who were enrolled within four weeks of a confirmed mild infection in 2024 and 2025.
The protocol combined cardiac MRI, transthoracic echocardiography with strain analysis, ambulatory ECG monitoring and a maximal cardiopulmonary exercise test at baseline, six months and twelve months. None of the imaging end-points moved meaningfully across the year. Left ventricular ejection fraction sat at 60.4 percent at baseline and 60.1 percent at twelve months; right ventricular global longitudinal strain shifted by 0.2 percentage points, well inside the test-retest range; and absolute peak VO2 was unchanged at 52.6 ml/kg/min. The only directional shift the authors flagged as worth tracking was a small drop in resting heart rate at follow-up, which the paper attributes to athletes resuming higher training volumes once cleared.
The clinical context matters. Earlier work, including a widely cited 2020 cardiac MRI series, raised concerns that mild SARS-CoV-2 infection might be linked to subclinical myocarditis or persistent fibrosis in athletes, and several federations introduced mandatory return-to-play imaging on the back of those reports. COSMO is the first study to tie a strict mild-disease inclusion criterion (no hospital admission, no oxygen need, symptom resolution by day 14) to a full year of structured imaging follow-up, and its sample size means a clinically relevant adverse signal would have been visible in the data. None was.
For runners returning to training after a mild infection, the practical implications align with the position the European Society of Cardiology and the American College of Cardiology have moved to over the last eighteen months. Cardiac imaging is no longer routinely warranted in the asymptomatic and the mildly symptomatic; testing should be reserved for runners with new exertional chest pain, palpitations, syncope or unexplained drop in performance, or for those whose return-to-training feels more difficult than expected after week two. The COSMO authors stop short of saying so explicitly, but their data effectively argue against population-level imaging screening for previously healthy endurance athletes.
The caveats are familiar but worth restating. The study was outpatient-only, so its conclusions do not apply to athletes who were hospitalised or who had ongoing symptoms beyond two weeks. The cohort skewed European and white, and minority recruitment was thin, although the authors note that subgroup analyses by sex, age band and discipline (running, cycling, rowing, team sport) were directionally consistent. And all imaging was performed at three high-volume centres with strain analysis read centrally — community-grade echocardiography may not detect the same subtleties. Even with those caveats, the trajectory of the cardiac-after-COVID literature in athletes has now firmly inverted from 2020's anxieties.