Histological and Physiological Adaptations of the Human Myocardium in Response to Chronic Endurance Exercise

International Journal of Anatomy and Physiology | Vol. 15, No. 9, September 2026 | pp. 19–27

DOI: 10.46882/2026/IJAP/001003

Review Article

Title: Histological and Physiological Adaptations of the Human Myocardium in Response to Chronic Endurance Exercise

Names of Authors: G. R. Müller¹, A. L. Rossi²*

Authors’ Affiliations:
¹ Institute of Cardiology and Sports Medicine, German Sport University Cologne, Cologne, Germany.
² Department of Physiology, University of Bologna, Bologna, Italy.

Abstract:
Chronic endurance exercise triggers extensive physiological and anatomical remodeling of the human heart, collectively referred to as the athlete’s heart. This review synthesizes current literature on the underlying histological, molecular, and physiological adaptations of the myocardium in response to prolonged aerobic training. Endurance training induces eccentric hypertrophy, characterized by a proportional increase in left ventricular chamber size and wall thickness. At the cellular level, cardiomyocytes undergo elongation through the serial addition of sarcomeres, accompanied by a balanced increase in myofibrillar density and mitochondrial biogenesis. Physiological changes include enhanced vagal tone, leading to resting bradycardia and an increased stroke volume via the Frank-Starling mechanism. Myocardial capillary density increases to match the structural hypertrophy, ensuring a balanced myocardial oxygen supply and preventing tissue ischemia. Furthermore, molecular signaling pathways involving insulin-like growth factor 1 (IGF-1) and phosphoinositide 3-kinase (PI3K) are up-regulated, steering physiological hypertrophy away from pathological pathways driven by angiotensin II. Myocardial interstitial collagen content remains stable or undergoes organized remodeling, avoiding the diffuse fibrosis seen in hypertensive heart disease. Understanding these adaptations is vital to distinguishing benign physiological remodeling from cardiomyopathy, ensuring accurate screening and prevention of sudden cardiac death in elite athletes.

Keywords: Myocardium, Cardiomyocyte, Eccentric hypertrophy, Endurance exercise, Physiological adaptation.

Manuscript Timeline: Received: April 15, 2026; Revised: June 30, 2026; Accepted: August 02, 2026; Published: September 12, 2026.

Citation: Müller GR, Rossi AL. Histological and Physiological Adaptations of the Human Myocardium in Response to Chronic Endurance Exercise. International Journal of Anatomy and Physiology. 2026; 15(9): 19–27. doi:10.46882/2026/IJAP/001003

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