Traditional echocardiographic measures of diastolic and systolic function—including mitral E-wave velocity, tissue Doppler e′ and s′ velocities, and LV twist—are not significantly different between endurance-trained athletes and untrained individuals when matched for heart rate during exercise, indicating these standard metrics are insufficient to detect training-related cardiac adaptations.

Endurance training makes the heart's main pumping chamber larger and more stretchy, so it can hold and fill with more blood between beats. Even when the heart beats at the same speed as an untrained person's, the trained heart fills faster and more completely because it can expand more easily. This allows it to pump out more blood with each beat, but the speed at which blood flows into the chamber or how fast the chamber twists doesn't change enough to show up on standard ultrasound tests.