Stretching is commonly practised as part of “warming up” and “cooling down” during training or sports sessions. Maybe your coach or personal trainer told you to do it and said it will prevent you from sustaining an injury.
There is a common misconception that your basic 15-30s stretch “adds more muscle cells”. However, the reason why you may find you can move your joint further or feel less discomfort after a stretch is actually because of what happens in the nerve and brain.
Let’s talk through what happens when you stretch your hamstring muscles
1.When your hammies are stretched, the receptor inside detects the muscle also gets stretched
2.As it is being stretched, the receptor will send signals up to your brain saying “this muscle is being stretched!”
3.Your brain then weighs up whether it is ok to let it continue stretching or send a signal of pain to prevent you from stretching it.
4.If your brain chooses the latter, you will feel the discomfort associated with stretching and not want to stretch it any further
5.But now that you have stretched it, your brain realises “hey the muscle can be stretched this far and it did not get injured!
6.The next time you stretch your muscle to that point, your brain will recognise that it is safe and not send a signal of pain.
7.As a result, you don’t feel as much discomfort and can stretch it a little bit further!
In other words, stretching helps by increasing your TOLERANCE to stretch, not by increasing muscle length
Page, P., 2012. Current concepts in muscle stretching for exercise and rehabilitation. International journal of sports physical therapy, 7(1), p.109.
Behm, D.G., Blazevich, A.J., Kay, A.D. and McHugh, M., 2016. Acute effects of muscle stretching on physical performance, range of motion, and injury incidence in healthy active individuals: a systematic review. Applied physiology, nutrition, and metabolism, 41(1), pp.1-11.