Current evidence on muscle hypertrophy in response to training at different muscle lengths is insufficient to establish definitive guidelines.

When muscles are worked, whether stretched or shortened, the buildup of metabolic byproducts like lactic acid and swelling inside the muscle cells triggers signals that tell the cells to build more protein. At the same time, stretching the muscle during exercise pulls on the fibers and creates tension, which also activates growth signals. These two pathways — one from chemical buildup and one from physical stretch — both lead to the same outcome: muscle growth. Because both pathways can work independently and produce similar results, training at different muscle lengths doesn’t consistently lead to more growth in one position over another.