Loading a muscle while it is long
Stretch-mediated hypertrophy refers to the observation that emphasizing the lengthened portion of a movement, where the working muscle is under tension while stretched, tends to produce more growth than training the same muscle only in its shortened or mid-range position.
Examples include deep stretch on the lowering phase of a calf raise, a chest fly that lets the pectoral lengthen fully, or a deficit position in a leg curl. The combination of high tension and a long muscle length appears to be the relevant stimulus.
How strong is the lengthened-position advantage
Several controlled studies report a modest advantage for lengthened-position or full-range training over partial work biased toward the short range, and the effect seems most consistent for muscles trained through a large stretch. The magnitude is meaningful but not dramatic, and findings vary by muscle group.
Training at long muscle lengths can be more fatiguing and can produce more soreness, so load and volume usually need to be introduced gradually. Range of motion should stay within pain-free, controlled limits. This is general educational information, not medical or rehabilitation advice.