In his book “Form and Function: The Anatomy of Motion, ” Evan Osar states, “research indicates many orthopedic injuries are related to weakness in the decelerators of the body or lack of eccentric control. Many injuries occur in the deceleration or slowing phase of motion.”
Before I go on, lets have a little review on exercise physiology. There are essentially three types of muscle contractions.
1. Isometric: contractions in which tension develops in the muscle but there is no change in muscle length (think pushing against a wall).
2. Concentric: contractions in which tension develops in the muscle causing the muscle to shorten (think arm curl where you lift the weight).
3. Eccentric: contractions in which tension develops in the muscle causing the muscle to elongate (think arm curl where you lower the weight).
In the realm of resistance training and/or rehabilitation, Osar notes that much of the focus is placed on force production or concentric contractions. Very little emphasis has been placed on force REDUCTION or the eccentric phase of motion.
During normal walking, the hamstrings function to decelerate extension of the knee during the swing phase. The quadriceps functions to decelerate flexion of the knee as the glute max functions to decelerate internal rotation of the knee during the loading phase (pronation). As you can see, lack of eccentric control can easily lead to knee as well as low back, hip and ankle dysfunction.
When all is said and done, many trainees (whether they’re athletes or soccer moms) would bode well by incorporating an equal amount of time to teaching force reduction (deceleration) and stabilization (isometric) as they relate to force production (acceleration).
A few general protocols I like to use with new clients are:
1. Low box jumps (learning proper landing mechanics, and hence deceleration). Teaching people how to land properly can go a long ways as far as preventing future injuries or kinetic dysfunctions. Essentially you take a low box or “stepper” and jump from the floor onto the box. For many, it’s easier said than done.
2. Split Squat Isometric Holds. These are great for beginners to teach stabilization. Basically you will stand in front of a bench and place one foot on the bench. From there you “squat” down with the other leg and hold that position for an allotted amount of time (usually 20+ seconds on each leg). You want to maintain an upright posture (shoulders back, chest high), and you want to make sure the knee is not caving in.
