Muscles That Control the Knee
Two sets of muscles control the knee: the quadriceps and the hamstrings. The quadriceps extend, or straighten, the knee and the tendon that connects the quadriceps to the shin also houses the knee cap. The hamstrings flex, or bend, the knee. Generally, the quads are stronger than the hamstrings but both sets of muscles must work together in order for the knee to remain healthy.
Eccentric vs Concentric Contractions
There are two different types of muscle contractions, concentric and eccentric. Concentric contractions are what we usually think about when we see the word contraction--the muscle shortens and the angle of the joint decreases. With eccentric contractions, the muscle lengthens and, with a few exceptions, the angle of the joint increases. Take, for example, a bicep curl. The act of lifting the weight causes a concentric contraction in the biceps muscle. In order to lower the weight, the bicep must slowly release and lengthen to lower the weight in a controlled motion. The slow release of the bicep muscle is an eccentric contraction.
Benefits of Eccentric Exercise
One of the biggest benefits of eccentric exercise is greater strength gains than with concentric exercises alone. Eccentric exercise also stimulates greater muscle growth. Most concentric exercises have an eccentric element built in; because, however, the primary focus is on shortening the muscle, they are not as effective as specifically designed eccentric exercises.
Stand with the feet hip-width apart next to a wall or table for balance. Shift the weight of the body to the right leg and slowly lower until the thighs are parallel to the floor. It should take a count of four or five to reach this position. Take care not to let the knees extend over the toes. Shift the weight back to both feet and rise to standing. Repeat five to ten times each leg.
Eccentric Hamstring Extension with Bands
Loop an exercise band around the heel of the right foot. Close the loose ends in a door or tie them around a heavy, stationary object. Bend the right knee so that the shin is parallel to the floor. Slowly lower the foot back to the floor. It should take a count of four or five to reach the floor. Once the toes reach the floor, bend the knee in one quick motion. Repeat five to ten times.
Stand on a step with feet hip-width apart. Step down, in a slow, controlled motion, with the right leg. When the right foot hits the floor, bring the other foot down. Repeat five to ten times each leg. Increase difficulty by increasing the height of the step.