Running Surfaces...do they matter?

Have you ever run off-road to give your body a break from the joint pounding pavement?

Or do you switch up your road workouts for a softer surface and feel as though your muscles are still fresh at the end of it?

These are common statements in the running community, but what does a change in running surface actually do to your body?

Picture yourself jumping off a box and landing on a hard concrete floor.  To cushion the impact you bend your knees and hips to absorb the force of the concrete pushing back.   Now picture yourself jumping onto a very large pillow.  Your legs naturally stiffen to respond to the forgiving surface.  The same goes with running surfaces.   A study done in the 90’s by D.P. Ferris et al.  looked at how our knee angle changes when running on different surfaces.  He found as the surface got harder our knee flexed more to absorb the shock.   Our bodies do this to maintain a consistent vertical displacement while running.  Too little vertical displacement and our bodies are jolted by shock.  Too much vertical displacement and our ability to run fast is diminished (picture running on a trampoline). 

When the knee bends further to cushion the impact on hard surfaces it creates are larger moment of force around that joint.  In essence, your muscles have to work harder when there is more knee bend.  Therefore when you are running on softer ground your body requires less muscle recruitment which equals decreased energy expenditure.   This is why your muscles may not be as sore after running on softer ground.

To my knowledge there are not any studies reporting the intrinsic joint pressures of the knee while running on different surfaces. 

So, running on softer ground makes it easier on the muscles that support the knee joint.  A great idea would be to do your recovery runs on a soft track or groomed trail to decrease the stress imposed on the muscles.  Doing so may just mean the difference between running injury free or having to watch from the sidelines!

Until next time, stay healthy my friends!

Dr. Adam

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