This is actually interesting thing to know. Our body muscles are attached to bones by tendons. When a muscle contracts it actually pulls on the tendons, where then tendons pull on the bone and cause the movement, like walking or exercising.
Two things you should know about the above fact.
Tennis elbow is the inflammation of the tendons in the elbow. A repeated strain on the elbow will produce this injury.
Secondly, as we age tendons become stiff and that is why it is harder for us to do things when we are older. Therefore, it is important to exercise all the time. Remember stretching is not only for the muscles, but more so for the tendons. With regular stretching you can avoid tendons injury by keeping them nice and elastic. Same applies to the muscles.