Muscles are always constantly tearing on a very small level and this is more apparent after exercise. You may wake up early the morning following exercise and feel achy - this is a sign that your body muscles have been stretched and may even be torn or damaged. Most of the tears are on a microscopic level but this can lead to more serious aches or pain if not treated.
Imagine that your muscles are like elastic bands. When you exercise, sit or stand for long periods or damage muscle tissue, your muscle will become shorter and tight. This would be similar to an elastic band which has knots tied into it.
So you can imagine that when the muscle tissue is tight it will pull into other structures i.e. bones, ligaments and tendons.
It's not just exercise that brings on small tears within the muscles. Repetitive movements and constant static posture, like sitting for long periods, can cause tears resulting in muscle aches and pains. At the end of the day the only thing that moves your bones (unless you have an impact injury) are the muscles.
Continual tension from the muscles will affect your posture. In other words your muscles can and will drag you out of position and affect your posture. This may cause problems or pain in areas of your body you might not even be using.