Stretching doesn't lengthen your muscle, despite what people assume
For years, improved flexibility from regular stretching was explained as the muscle literally getting longer over time, letting the body move through a greater range of motion. Modern research using ultrasound and MRI doesn't back this up: a muscle's resting anatomical length after a stretching program stays essentially unchanged, even when flexibility improves noticeably.
What actually changes is stretch tolerance: over time, the nervous system allows the muscle to stretch further before a protective reflex (contracting in response to excessive stretch) kicks in and stops the movement. Put simply, regular stretching doesn't train the tissue itself — it trains the threshold at which the brain decides further stretching isn't safe.
That doesn't make stretching pointless — greater stretch tolerance genuinely expands usable range of motion and can lower the risk of certain injuries. But it's worth understanding: the point of stretching isn't to physically 'lengthen' the muscle, it's to teach the nervous system to safely allow a bigger range.