In people with post-COVID, abnormalities in heart function are increasingly being described. For a long time, it was assumed that these changes were mainly the result of cardiac deconditioning: loss of fitness due to prolonged inactivity. A recent publication in the British Journal of Sports Medicine critically reexamines this assumption. NMCB researchers Rob Wüst and Braeden Charlton from Vrije Universiteit Amsterdam contributed to this review.
The authors show that the cardiac abnormalities found in post-COVID do not always fit the classic picture of deconditioning. Although inactivity can contribute to fitness loss in some patients, several studies point to additional underlying mechanisms.
For example, in cardiopulmonary exercise tests, some patients show preload failure: an insufficient filling of the heart during exertion. There are also indications of inflammatory changes and scarring in the myocardium in a subgroup of patients. This does not align with the usual pattern of simple deconditioning.
Additionally, data are accumulating on mitochondrial dysfunction and endothelial dysfunction in various tissues. Disturbed energy production in cells and damage to the blood vessel walls may contribute to reduced oxygen uptake and dysregulation of the exercise response. Whether these processes also occur directly in heart tissue is still unclear. Well-validated animal models are lacking, and longitudinal heart biopsies are scarcely available.
This does not mean that deconditioning cannot play a role. In patients who have been bedridden for an extended period, fitness loss can certainly contribute to complaints. However, the heterogeneity of the findings makes it clear that this does not explain the full mechanism.
For clinical practice, this means that fatigue and exercise-related complaints in post-COVID should not automatically be interpreted as a result of deconditioning. When changes are observed in heart measurements, careful assessment of the underlying cardiovascular mechanisms is required. Read the full scientific review here:
👉 https://bjsm.bmj.com/content/early/2026/02/09/bjsports-2025-111387.long