Stretching does not alter a muscle’s tissue structure or length.
Holding the stretch for 2 minutes is so that the cells can actually "wake up". After this time, you go into your PAILs RAILs and that is when you get the any sort of change. Over a long period of time of course. With enough time given enough stretch signal or load, the CNS will allow the increases of ROM to occur. This is an alteration in the way the CNS controls the tissue being stretched.
In order for the CNS to allow further movement, it must alter the stretch reflex. (Natural governed mechanism). Stretch reflex regulates how long a tissue is allowed to stretch.
Stretch reflex threshold is set at a certain length in which it feels “safe.” The stretch reflex will prevent ROM far before there is a chance for injury to occur as a result of elongation.
Muscle tissue vs. Connective tissue, also.
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🛑BUT ATTENTION 🛑
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There are some minor changes that are induced with static stretching. Just recently more research is coming out on this topic. A small amount of sarcomerogenesis does occur if stretching is prolonged - this is ramped up SIGNIFICANTLY with the application of active inputs (iso's, then ENG).