This condition is often caused (as you might guess) by playing a lot of tennis. Then again, it can also be caused by a shock to the elbow so isn’t unique to tennis. For instance, squash players, badminton, rugby and hockey players can all experience it too. The shock to the elbow results in inflammation in the forearm muscles which then goes on to cause pain.
A group of three muscles situated from behind the knee to the pelvis, the hamstring muscles allow the knee to bend. Over-stretching can damage them as can vigorous sport or intense gym work. Not stretching prior or after exercise can cause them to become shortened.
How to tell if you have hamstring strain
A different walk
Stretching causes pain and the area feels tender
That area (where it hurts) feels weak and as if it’s about to collapse