Do not hit with the heel
When you stretch your stride too, rest your feet before your center of gravity and landing hard on the heel. This impact is transferred directly to the knees, which are not intended as shock absorbers. In addition, when nailing the heel on the floor you are slowing your movement forward, expending more energy. The way to avoid this is to advance the body and let the land foot behind your center of gravity.
Do not lift your knees
Many magazines brokers advise you lift your knees to increase stride. Do not do it, so you only get to take the body feet first and hit the back heel. Let your heels rise up behind you at the end of the stride.
Do not let stiff legs
Keep your knees slightly bent to rest your feet on the ground. If the leg comes into contact with the ground fully stretched greatly it increases the impact on the heel and knee.
Do not run with crooked feet
Your feet must be aligned with the direction of movement. If the feet are supported at an angle to your career, equivalent to someone twist your knee ligaments three times per second and you make sure tendinitis on the inside of the joint.