During endurance training, several physiological changes occur, including increased muscle efficiency, enhanced cardiovascular capacity, and adaptation of the body's energy systems. Regular training leads to improved stroke volume, allowing the heart to pump more blood with each beat, thereby enhancing oxygen delivery to muscles. Additionally, the body becomes more efficient in utilizing fat as a fuel source, sparing glycogen for higher-intensity efforts. Over time, increased mitochondrial density and capillary networks facilitate better oxygen exchange and utilization, contributing to overall fitness and performance improvements.