The cardiac muscle's ability to resist fatigue during continuous activity is primarily due to its high mitochondria count. Mitochondria are the powerhouse of the cell, producing ATP through aerobic respiration. This abundant mitochondrial content allows cardiac muscle to generate a steady and efficient energy supply to sustain continuous contractions without fatigue. Additionally, the rich mitochondrial density supports the heart’s reliance on oxidative metabolism, essential for maintaining its relentless activity. This feature is critical for the heart’s endurance and function throughout life.

Reference: Guyton and Hall Textbook of Medical Physiology, John E. Hall, 13th Edition.