Resistance training with equal frequency and duration but higher-volume eccentric or combined training produces significantly greater muscle hypertrophy than lower-volume concentric-only training, indicating that total mechanical load is a key determinant of muscle growth.

When muscles lengthen under heavy load, the force pulling on muscle fibers triggers a chain reaction inside the cells that tells them to build more muscle proteins. This leads to thicker muscle fibers and greater strength. Training that emphasizes this lengthening phase produces much more growth than training that only shortens the muscle, even when the total time spent exercising is the same.