system
Given the following post, respond as if you're commenting on Reddit:
human
How does stretching actually make the body more loose and flexible over time?

I recently started kickboxing and I'm extremely stiff. However, my legs are gradually becoming more flexible and i find the process fascinating!

EDIT: Wow thanks for all the interest everyone, learning a lot. It's kinda crazy we still don't have the complete facts about how muscles become flexible through yoga and stretches.
gpt
There are 4 things that limit your mobility range (in very laymans terms)

1. Length of muscles (least of an issue)
2. Length of tendons (very hard to change)
3. Bone structure (for some specific stretches)
4. Neuromuscular response (most important issue)

&#x200B;

1. Length of muscles can be changed through stretching similar to tearing your muscles through weightlifting. But unfortunately you can't approach stretching with that mindset as there will be other things that will impede you from making any gains. "No pain, no gain" - doesn't work with stretching. Pain = injury/slow recovery/loss of mobility/one step forward two steps back. Lengthening of muscles is more of a passive thing that can't be targeted, it just happens when you stretch properly. Stretching through pain can work if youre really young and can recover quickly but in general it is considered a bad, inefficient and outdated practice.
2. Length of tendons is something that is very hard to change and if you didn't stretch through puberty it's very unlikely you'll reach a contortionist level flexibility. With that being said something like splits would still be achievable by most even inflexible people. There are simple physiological tests you can perform to see if your body would actually be capable.
3. Bone structure. Some stretches like a "perfect" ballet turnout require certain bone structure and again can only be achieved through stretching through puberty.
4. Neuromuscular response. Now this is the main culprit of stiffness. Your brain likes to keep your body safe and will contract and tense up muscles if it deems them extended past the safe point. This part of brain is autonomous and cannot be overriden it can only be "trained" by tricking your brain into thinking that the movement range you're trying to achieve is safe. Don't push too hard, relax, and do it often. Frequency over intensity is the key here. It's 10 times better to stretch 20 times a day for 1 minute than one time for 20 minutes.