Question: why do people pull their muscles?

Mark Burnley answered on 13 Jun 2011:

Jenni might be more help on this one! Because the muscles are made of proteins that can contract, these proteins can also be stretched. If you stretch them too far or too fast when you are using them, you can split the fibres that make up the muscles, and this causes pain as well as making it impossible to use the muscle. Have you ever done lots of running and jumping on one day and then felt really sore the next? Believe it or not you’ve pulled the muscles then too, but not completely. In this case you have damaged some of the fibres, but not enough to realy be injured, and the soreness you feel is the result of the muscle trying to repair itself (which is why you don’t feel it straight away).