Histomorphological Evaluation of Myocardial and Coronary Microvascular Adaptations Following Controlled Long-Term Endurance Training

International Journal of Anatomy and Physiology | Vol. 15, No. 9, September 2026 | pp. 353–364

DOI: 10.46882/2026/IJAP/000197

Article Type: Original Research Article

Title: Histomorphological Evaluation of Myocardial and Coronary Microvascular Adaptations Following Controlled Long-Term Endurance Training

Names of Authors: Diego M. Rossi¹, Lucas A. Silva²

Authors’ Affiliations: ¹Department of Anatomy, Institute of Biomedical Sciences, Federal University of Rio de Janeiro, Rio de Janeiro, Brazil; ²Department of Physical Therapy, Faculty of Medicine, University of São Paulo, São Paulo, Brazil

Abstract:
Physiological cardiac hypertrophy induced by exercise involves coordinated growth of cardiomyocytes and capillary networks to avoid ischemia. This study investigated the histomorphometric balance between cardiomyocyte cross-sectional area and coronary microvascular density following a structured long-term endurance protocol. Thirty adult male Wistar rats were assigned to a sedentary control group (n = 15) or an exercise group (n = 15) subjected to a progressive 12-week swimming protocol (60 min/day, 5 days/week). Left ventricular (LV) tissues were processed and stained with Hematoxylin and Eosin (H&E) and fluorescein-labeled isolectin B4 to visualize capillaries. The exercise group displayed physiological cardiac remodeling, with a 24.5% increase in total heart weight to body weight ratio (p < 0.01). The mean cardiomyocyte cross-sectional area in the LV grew significantly to 342.5 ± 14.8 μm² compared to 264.2 ± 11.2 μm² in controls (p < 0.01). Importantly, capillary density in the myocardium rose proportionally from 2150 ± 110 capillaries/mm² in controls to 2840 ± 140 capillaries/mm² in the exercised group (p < 0.001). The capillary-to-myocyte ratio increased from 1.15 ± 0.05 to 1.48 ± 0.08, indicating balanced angiogenesis. These quantitative measurements show that physiological hypertrophy involves parallel microvascular expansion, ensuring adequate perfusion to supported myocardial tissues.

Keywords: Cardiomyocyte Hypertrophy, Angiogenesis, Endurance Training, Left Ventricle, Isolectin B4, Wistar Rats

Manuscript Timeline: Received: August 03, 2026; Revised: September 08, 2026; Accepted: September 19, 2026; Published: September 30, 2026

Citation: Rossi D.M., & Silva L.A. (2026). Histomorphometric Evaluation of Myocardial and Coronary Microvascular Adaptations Following Controlled Long-Term Endurance Training. International Journal of Anatomy and Physiology, 15(9), 353–364. DOI: 10.46882/2026/IJAP/000197

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