Getting the Most of Ground Reaction Forces

Here is the third installment of trainer, Todd Walbert's blog.  Read on to find out what he has to say about "ground reaction forces".

I changed my mind on the topic for today's blog.  I want to talk about "ground reaction forces" or GRF for short.  First, let's define GRF...it is equal in magnitude and opposite in direction to the force that the body exerts on the supporting surface through the foot.  That's a big mouthful but in layman's terms it refers to the reaction of the force the body exerts on the ground.  Now, on with my thoughts.  I see so many people running on the treadmill while at PROMATx.  Most people know walking or running outside is better for you, but why?  It's because you have to work harder when not on a moving track.

Bear with me as I talk a little about the science behind GRF...it might get a little technical but hang in there!  At the University of Kentucky, I participated in a lab that studied GRF.  We ran as natural as possible over a force plate in the ground.  This plate was an aluminum alloy plate, approximately 14-16" rectangle, that was flush with the ground.  When we took a step on the force plate, it measured the "multiplanar force" or "angular pressure" exerted on that rectangular plate.  In this lab, we chose to measure the vertical positive and negative loads acting on the plate.  All of this information was, of course, computer generated but what was taken from this lab was that when you are on the treadmill you are absent of the "propulsion phase" of running/walking.  When moving forward on the ground, you have to "propel" yourself forward to keep moving.  On the treadmill, the belt carries your foot back, then your hip flexor muscles are used to step forward.  In other words, you have to work harder to move yourself when you are running/walking outside versus traveling the same distance on a treadmill. 

How do you account for the lack of the "propulsion phase" when on the treadmill or, in other words, get a better workout?  First, no healthy person should ever be on the treadmill with 0% grade/incline.  Try it, then spread the word.  On the same note, raising the incline to a crazy high number (thereby increasing the propulsion needed to keep up with the moving track) which causes you to hold onto the heart rate handles is another gym "don't".  [Refer to my last blog on "Gym Etiquette".]  While you are holding on and walking up this "Mt. Everest" hill, take a gander down and see what your heart rate does.  Does it go up?  Most likely it drops slightly while you are holding onto the handles.  That should be a clue that holding onto the handles of the treadmill (or for that matter, any cardio equipment) lowers the efficacy of your workout.

So, it's too hot outside to run/walk or the weather is not cooperating or you just would rather be on the treadmill.  How can you take advantage of this propulsion phase?  Use at least 1% grade/incline on the treadmill to give the feeling of a climb.  When you get used to this level then try to go back to 0%, it feels as though you are going downhill.  If you insist on using that crazy high level of incline, you better keep your hands off of those handles or I'm going come by and punish you!!  Give it a try.  You can even test yourself by comparing your run/walk outside versus that on the treadmill at 0% grade/incline.  You'll see that outside is harder, regardless of environmental factors.  

PS...this blog was not intended to bash treadmills.  I can think of hundreds of ways to effectively utilize this revolving belt!  Come and see me for details.  You won't regret it!!