When you create stresses on a muscle in the same spot over and over, the body tries to protect it and strengthen is by creating myofascial tissue. This is sometimes called scar tissues, knots, trigger points, or adhesions. When this happens it shortens the muscle therefore placing stress on the joints.
It's like a rope, if you tie knots in a rope, it is stronger, but it is also shorter. This is what happens with the muscles. `You can do stretching which lengthens the muscle some but as long as the knot is there the muscle cannot be at its optimal length.
With myofascial release, pressure is placed on the knot which allows it to release and puts the muscle back at its proper length. It normally takes 3-4 sessions to completely release the knots but in more severe cases it can take up to 6; however pain relief should be felt after the first.