THE PHYSICS BEHIND RUNNING FORM

Kaisa came to see me because she is gearing up for marathon running and triathlon sporting events.  She is serious in her pursuit and her eyes are turning towards Ironmans.  In response to the time we had the most important motor ability to these skills she is embarking on is running.  Running imposes the most force on the body and this is where a tri-athlete must gain the appropriate skill that will govern all the other abilities.  Learn the skill of running using efficient mechanics and you will see how some of the same principles apply to cycling and swimming, improving efficiency.  Running is our benchmark to rehab and performance for all athletes.  At the BFPA running is our speciality however our knowledge in cycling and swimming biomechanics our closely followed for the pursuit of the tri-athlete.

General over view:  Kaisa is a confident runner and brings strength and good posture to her heel striking running style.  Good posture will limit injury in any running style, however below you will get to understand how Kaisa can truly improve her game by understanding how nature designed us to run.

By looking at running with physics in mind (not coaching) we can see where athletes are or are not utilising potential energy.  Potential energy comes from taking the vertical force, what gravity gives us and utilising this force into horizontal force; running forwards.  When you capture an athlete like this in the air there are several key points we can look at where energy is being wasted.  The first place I would look is the huge v-shape of the legs.  This shape creates excessive torque in rotation where the upper body excessively counter rotates to help balance the force of the two limbs which are at their furthest point away from the general centre of mass (GCM) of the body whilst in motion. As a rule of thumb, when forces go up due to momentum the body is designed to lesson the joint torques not increase them. Secondly this miss balance in the air sets up Kaisa for an aggressive heel strike.

With good strength Kaisa has brought herself back to good posture on loading.  Chest facing forwards, alignment through spinal column and luckily for her knee it is soft on loading.  However her GCM is behind her ball of foot (BOF) as she heel strikes. What goes down must come up and the red line emphasis a breaking force experienced in heel striking.  The skill of running is about minimising this breaking force by getting the foot strike under the GCM.

Everyone goes through running POSE which is the last picture in this sequence where the GCM is directly above the BOF.  It is the only way to move forward.  An important skill of running is about how you arrive to this point.  Kaisa takes in running terms a long time to get to what is termed POSE (form at support phase).  She loses valuable height and increases her exposure to her time on the ground which is associated with injury.  Look how her blue line around her waist drops below the hedge line in the background.  With good form there would be some degree of drop to gain elastic energy (triphasic system of muscles) but not this much.

Back to the Physics of running and this picture represents a term we call gravitational torque.  The red line represents the angle of fall.  This is how the GCM has accelerated beyond its starting point which was directly above the BOF.  This allows the GCM to effectively fall forwards from it’s pivot point from the base of support (BOF) through the dynamic lever system in the body.  If we are able to hold our height (running strength) then all this energy would be levered into horizontal force.  However in Kaisa case she has lost lots of height and now has to regain it by excessively pushing off through her leg.

You can see her blue band around her waist is now higher than the hedge line behind her.  She continues to fall forwards yes but at a high cost of imbalance which creates the v shape in the first sequence, which has the effect on the braking forces experienced which then determines how long you can sustain this abuse, which turns into injury that 85% of runners frequently suffer from year to year as researched by the ACSM in 2005.  In all it is a very inefficient way to run.  Where in a session you can look like this….

After coaching Kaisa what it takes to get closer to good form running we re-assessed her running mechanics.

The v-shape has gone.  The leg is still trailing quite far behind which opens that chest up to rotation however it is not as excessive and therefore much better.  Only adaptation (6 week periods) of practising good form will you find her body smarten up to allow a faster pull through of her back leg, lessening the weight of the limb left behind.  By quickening this action the limb’s centre of mass gets back to the GCM allowing better balance and effectively less drag on the body.

In one session and back into shoes Kaisa has become a midfoot striker.  Her GCM loading a lot closer to being over the BOF.  Therefore the breaking force is reduced, shown by the more vertical angle of the red line compared to her first analysis.

It now takes Kaisa less time to get her GCM over BOF.  Notice how her leg is a lot stiffer, not so bent.  Therefore not losing so much height.

Interestingly she gets more angle of fall before she breaks POSE (form at support phase) compared to her first style of running.

So less height loss due to lessening the breaking force = in more distance covered in the horizontal plane.  If you are a runner this must be the efficiency you are looking for.

Luckily for me as a coach this style is how the body was designed to run and to top it all, it is kid like, light, agile, fast and super fun.

Kaisa has done really well to transform to this skill in one session.  However it must be pointed out that she still lacks lower limb strength which in my experience is an exact representation of her hip strength too.  From the picture you can see her heel is quite high off the ground (especially when you take the heel lift of the shoe into account).  This represents a sprinters mechanic although she is only at running speed.  (How can we tell that from a still photo is her angle of fall)

Finally the excessive push off is not going to change over night for the more athletic student.  It must be said it is easier to coach a none runner who has not embedded years of compensatory strength to get a job done.  Kaisa still excessively pushes off producing too much vertical force still.  However her pull through is quicker hence her shape in the air (no v-shape) improves and if she does not go out side the boundary of what her lower limb can take with this new training she will gain the necessary strength which will adapt her skill.

If she experiences painful delayed on set of muscle soreness (DOMS for more than 2 days) then skill will be compromised both in the session causing the DOMS and future sessions.  Therefore running form will suffer through compensation.  It is the runners who still get injury that haven’t quite got on top of their form.  Good form eliminates common injury.  If you are doing performance activities which inevitably take you slightly away from good form be sure you keep on practising good form to bring you back in balance.  

Gaining the right strength in her ankle (lower limb) will unable her more free momentum and as her muscle tone acquires the right coordination, stiffness and ability to relax.  

If Kaisa follows what felt right on the day and practises the new balance point which is a big challenge for anyone who hasn’t this skill already and she will transform into a very good runner.

However to obtain good form is a whole different psychological matter which takes time practising the skill of movement.  The best in the world call it a life time of practise.

Change comes from learning new skills.  For Kaisa in her first session it was based around the Barefoot Deep Squat and learning the skill of barefoot running.  This required changing posture from foot mechanics to head alignment and everything in between, whilst teaching the body a new kind of coordination.  The one the body was already wired for..

One of the most valid questions is why this shape then?  If this is all wrong why does the body choose it?

Everything we do comes down to metabolic cost.  As an organism it is concerned about how much energy it is using.

Elastic energy is a kind of free energy we have designed to utilise through the arches in our body and its links to ligaments, tendons and muscles.  The all important one (which we have all lost considerable strength in because of being a shod population, especially when we look at shock absorption technology shoes) is in our foot which gives the plantar fascia potential energy when the arch is flattened.  Our leg uses the same principle with a soft knee (be aware of perception of soft knee, not bent like Kaisa’s), and our curves in our spine all utilise potential energy.

Through lack of conditioning (losing the skill for running) we lose the effectiveness of elastic energy.  This creates the first issue in the lack of speed in our coordination and this then falls prey to what the body knows as the most efficient mode of transport – walking. 

Walking utilises more rotational torque (a longer stride (v-shape)) to provide enough torque to enable motion.  Enter the shape you see above a mix of running and walking.  Jogging is actually quite a spot on term for slow running, because it is neither hear nor there and it is only made consistently possible by shoe cushioning taking away the pain of what the heel would feel landing first without cushioning.   Walking is a heel to toe action but only deals with one body weight where in running there is twice as much force.   Hear enters the main role of elastic energy utilising twice as much force whilst protecting the body from injury by lessening the joint torques.

About the author

Rollo Mahon has an academic background in Sports Therapy.  His academic journey has led him through various athlete performance accreditations where he has specialised in the science and biomechanics of barefoot running.  His search has been to find the solution to injury free biomechanics and therefore better performance, which has been cemented by the science of Barefoot Science.