Updated: Nov 29, 2019
Reading The Science of Stretching: A Review
Mitchell, Jules, M.S., California State University, Long Beach, 2015
Muscles have the capacity to contract and lengthen. But this capacity - eccentric contraction in the context of stretching - can only be trained against an applied load or force, such as gravity, externally applied or internally generated forces or loads. Muscles don't lengthen by themselves. In the context of stretching a tensile load is applied to a target muscle and surrounding connective tissues. Hence, elongation stands in correlation to the applied load, the muscle’s composition and its qualities as well as those of the surrounding structures.
Muscles have a mechanical limit or range – a maximum amount of deformation they can withstand. Stretching within this limit, muscles will elongate and return to their resting length after the load is removed. If the applied load or duration exceeds this limit, it can lead to injuries and tissues tears. Hence, stretching exercises cannot actually increase muscle length. Muscles have attachment points and these do not change via stretching.