Ground Reaction Force: The source of your power!

Newton's third lawDo you remember learning Newton’s third law in a science or physics class?  Don’t worry, we didn’t think so!  This is the law that states “for every action, there is an equal and opposite reaction.”

Well, in a nutshell, Newton’s third law explains ground reaction force.  When we run, jump, throw something, etc., we push against the ground to get power, and the ground returns the exertion of the force to help us get that power.  If this doesn’t make sense at first, imagine trying to throw a ball while treading water in a deep pool.  Clearly, without a stable surface to push against with the legs, a person in a pool could not propel the ball the distance he could if he were standing on firm ground.  In a pool, the legs and torso can do relatively little to help, so the shoulder, elbow and wrist joint must produce the majority of the force necessary to throw the ball.

If muscles in the hips and legs, particularly the gluteus medius, are weak or injured, then the scenario on land is not much better than that in water!  When we push against the ground and the ground returns the exertion, the joints of our bodies must transmit this force in the best anatomical and most efficient way possible.  In other words, all the muscles of the body must be recruited at the right time to accomplish the task at hand.  Muscles must “fire” sequentially to prepare the body to hit the ball, leap the hurdle or perform the double back flip with a twist.  Thus, if any muscle along the kinetic chain is weak, underused or injured, then the transmission of forces will be inefficient and faulty, and other body parts must take on more work to make up for the “weak link.”

Using the tennis serve as our example (see chart below) 54% of the ball’s speed should come from the trunk and back, hips and legs.  Fifty four percent!  This means that before the shoulder even becomes involved in the serve, the body from the shoulders down generates more than half of the power that gives the ball its speed.  Of course the remaining power comes from the upper body:  the shoulder joint is responsible for 21% of the power, the elbow, 15% and the wrist, 10%.

Ground Reaction Force for Tennis Serve_Pilates

If the gluteus medius is weak, the torso, back, shoulder, elbow and wrist compensate for the lack of power by taking on more of the force.  As discussed in a previous blog, the gluteus medius is a key stabilizer of the hip, especially when the weight is on one leg.  When “winding up” for the serve, the body’s weight is on the same leg as the serving arm.  The muscles are loaded with power and funneled into an explosive serve.  A weak gluteus medius results in decreased power and INCREASED potential for injuries.  In fact, research shows a weak gluteus medius contributes to shoulder and elbow injuries not only in tennis but in baseball, swimming and golf as well.

What can you do?  Well, strengthen your gluteus medius of course!  In our previous blog, we listed all the Pilates exercises that are great for doing just this, “Side Leg Lift Series,” “Side Lying Scissors,” “Side Lying Clam and Book,” etc.  But, unfortunately, if the firing pattern for hip abduction is faulty, the TFL (tensor fasciae latae) fires BEFORE the gluteus medius.  Ideally, the gluteus medius fires before the TFL, but the reverse is true for many people.  No matter how fabulous a Pilates instructor you are, teaching someone NOT to use a muscle is far more challenging then teaching them to use one!

This is where ActivCore is absolutely ideal!  Because the Redcord system allows for the off-weighting of clients, chronic “misfiring” during hip abduction can be remedied without complex imagery, vocabulary or body awareness.  The reduced load enables the client to perform hip abduction with the proper sequencing of muscle firing. Pictures 1 and 2 below shows the regular Side Lying Abduction exercise and pictures 3 and 4  shows the same exercise off-weighted. For more information on ActivCore or the Redcord system, please visit their respective websites at www.activcore.com and www.redcord.com.  If you would like to enroll in the teacher training for ActivCore, please visit our teacher training page for upcoming training dates!

activcore sidelying abduction Picture1activcore sidelying abduction Picture 2

activcore sidelying abduction Picture3activcore sidelying abduction Picture 4

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July 16, 2009. Tags: , , , , , , , , , , , , , , , , , , , , , , , , , , . ACTIVCORE®, Pilates on Fifth Postings, Pilates Posts, The Pilates Center of New York Postings, UltimatePilatesWorkouts.com Postings.

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