Treadmill Running vs. Road or Trail Running

Ever wonder why switching from running on a treadmill (TM) to running outdoors on the road, track, or trail seems so much harder?  Well, there are a few reasons for this!  When running on a TM, the work coming from your muscles are being more or less minimized due to less work being performed on a TM when running (unless...we'll get to this).  There is also less energy being absorbed through your body when running on a TM.  This factors in to overall body fatigue and fatigue in the primary running muscles.  The amount of force absorbed through your foot, leg, thigh, and trunk are less when on a TM.  These are the two main reasons why of running on a TM is less vigorous or exhausting compared to outdoors.

The following details these 2 specific reasons:

Reason Number One:

When running on a TM, less muscle recruitment in your lower extremities are occurring.  Therefore, if there's less muscle recruitment, then there is less demand for oxygen to the working muscles.  The reduced muscle recruitment comes from when your foot lands in front of you on the TM belt.  At this time your foot and leg are being "carried" backwards by the speed of the belt and TM motor.  You are not fully propelling yourself forward.  The amount of force coming through your lower extremity is equal to the amount necessary for you to remain running in place on the belt (I think this is along the lines of Newton's Second Law - The acceleration of a body is parallel and directly proportional to the net force acting on the body...I've probably skewed that some :))  Simply stated, you are not actively propelling yourself forward!  

Here's an example, if you are running outside on a track, you are required to push the mass and weight of your body forward to traverse distance.  The force required to do this is much greater than on a TM. If you are running in an all out sprint, then the amount of muscle recruitment increases significantly as does the oxygen demand if this sprint is maintained for a long enough period of time that your immediate supply of blood/muscle/ATP (many of you may remember the days of suffering through having to memorize the Kreb's Cycle in biology) glucose is depleted.

When running on a TM, there is just enough work being done to advance your foot quickly enough forward so as to maintain your position on the TM and avoid being carried off the TM backwards (you ever watch The Biggest Loser?  Happens all the time!).  On a TM, you are not pushing your body weight and mass forward, you are just maintaining it in place.

But now we have to get into a little more physics.  When running on a TM it's like running in a vacuum.  No wind friction co-efficient or drag on your body has not been taken into consideration.  If you think this doesn't make a difference, then go back to the Olympics held in Mexico City.  Or consider how much farther a football can be kicked or thrown at high altitude such as Denver, CO at the Denver Broncos stadium.  We can take examples from drafting in cycling and drafting off of other runners.  It's a common practice in open water swimming competitions to draft off of another swimmer to conserve energy.  Yeap!  Even with swimming you gain substantial energy savings by swimming at the feet and in the wake of another swimmer.  The drag co-efficient is the one variable that can not be duplicated when running on a TM unless there is a fluctuating change in TM elevation to mimic a tailwind, headwind, downhill, and/or uphill running.  It would still be difficult to mimic an oblique tailwind or headwind.

So, here's what you can do to equalize TM running with running outdoors.  If you are used to running outdoors but for some reason you have to change up your run and move indoors, you can assimilate outdoor running by increasing the grade/elevation of the TM between 2.5% - 3%.  By doing this, you now have made TM running equivalent to running outdoors but on level terrain and without the body drag co-efficient.  Anything above 3% elevation puts you into the "running up a hill" category or "running into a headwind" category.

Reason Number Two:

If you have ever shopped for a TM and have seen in the description referencing a "cushion flex suspension system" running surface or a "low impact springboard running platform", well it's because the running surfaces on a TM do provide a very forgiving surface.  If you have a running technique in which you land directly and with significant force through your heel, the fatigue factor that this will have on your body, muscles, and joints will be significantly less.  The running surface on a TM will absorb the energy from a hard direct heel strike.  Now, let's say that an individual is transitioning to running outdoors on a path, pavement, up and down hills, or just a much harder surface.  The amount of overall body fatigue will manifest itself quickly, but last only a short period of time as long as the transition is done properly.  The signs of this manifestation will be sore muscles, knee, hip, ankle joint soreness, and possibly mild joint swelling in the lower extremities.  No need to worry though!  These symptoms are simply from attenuating new workloads, increased muscle recruitment, and end waste product from the body's increased muscular activity and joint force attenuation that comes with the territory of a "less forgiving" surface.

Just as our muscles become sore following the start of a weight training program or an increase in a current training program, our body needs to adapt to running on terrain that it is not accustomed to running on.  Just as muscles adapt to increasing workloads, the lining of our joints (joint articulating cartilage) will need to adapt to the increase in force.  This force affects multiple tissues and structures such as our muscles, nervous tissue, and joints.  The articular cartilage becomes dense up to the point that it is able to withstand the new forces.  It is no longer "soft and pudgy" from TM running.  The articular cartilage will become more dense, stable, and less prone to injury.  The joint effusion or swelling that may occur is increased synovial fluid within the joint and its' capsule.  The swelling in a joint relative to what is being discussed here is not blood!.  Your body is operating under its' design.  It is adjusting to your activities.  Just as we build calluses on our hands through the friction of gripping, the articular cartilage will toughen up to accommodate our activities.

Here's an editorial for the running cynics that swear on their lives that running can severely damage the knee and hip joints.

For the cynics out there, if blood were present, bruising would also be very apparent.  Pain, and not just a small amount of pain as would be present from mild joint swelling, a large amount of pain would be present!  If blood is present in a joint, it usually doesn't go unnoticed and the person would out of necessity seek medical attention.  Once the physician made his diagnoses, it's typical that the joint would be drained via a needle.

You see, blood is toxic to articulate cartilage.  Blood can quickly deteriorate the cartilage in a joint.  Each joint in our body has a capsule around them.  This includes not just the larger joints in our body but the small joints in our hands, toes, and the facet joints in our spine.  The fluid inside a joint is the lubricating synovial fluid.  The synovial fluid in a healthy joint is clear and is the most slippery substance you'll ever experience (seriously though, don't cut yourself open just to check this out!).  Synovial fluid in a joint of which blood is present has a milky red to dark red appearance depending on the severity of bleeding in to the joint.  A grade II or III ankle sprain is a good example of a torn joint capsule that is  accompanied by marked swelling and bruising (not just joint effusion).  The synovial fluid in a joint with moderate to severe osteoarthritis has a milky yellowish appearance.

Back to our original topic...

So, in summary, the underlying message is: 

• Running on a TM can be assimilated only so much to mimic running outdoors.  You can get close, but duplication of some variables are not possible.   
• When transitioning to running outside, it's recommended that you assess your running mechanics and see if you could benefit from running with a less forceful heel strike.  Because of the forgiving surface of a TM, it's easy to develop an inefficient stride.  By landing hard with your heel, mechanically this means that your knee close to full extension and your body is absorbing an unnecessary amount of force.  
• Remember, when using a strong heel strike, you lose a significant amount of your forward momentum, more time is spent on that leg during the single leg stance phase, and more energy is required to maintain forward momentum and speed.

As usual, please feel free to contact me with any inquiries at:  bsenska@therightfeet.com

Happy Bipeding!

Brad Senska, PT, DPT, BS, ASTYM.

bradsenska@yahoo.com