September 2020

The Dirty Truth About Being Biped

Image by fleetfeettucson 2020

By Jay Segel, DPM; Sally Crawford, MS; Grace Juriel; and Jason Kraus

What bears don’t know didactically about forces, shock, and kinetic chain, they understand naturally, instinctually, and it is evidenced by the way they move. Bears can stand on two legs, play, pose, and walk as bipeds do, but when it comes to motion involving speed, safety, or regularity, they function as quadrupeds. For those who make the argument that this is learned behavior, a good response might be, why that behavior?

Moving and running solely in biped fashion has its disadvantages compared with the reduction of force dissipation throughout the multiple weight-bearing limbs of quadrupeds. Although the movement is as old as humankind, perhaps the original dirty truth is that running is instinctual not behavioral. Humans run on trigger; they run for all sort of other reasons too, but they run in a challenged manner because we evolved as functioning bipeds.

There are some very inconvenient truths about human bipedal walking and running relating to collision dynamics, which need to be addressed here.  From the get-go, let’s identify some of the problematic relationships between form, function, and physics.

3-D Foot vs 2-D Surface

The most fundamental and foundational dirty truth is that we have a 3-dimensional foot of limited mass, colliding with a 2-dimensional support surface of relatively unlimited mass. This is a battle the foot cannot win. Indeed, this is a battle the foot does not win over 4 million times a year based on a 12,000-step-per-day average. What the foot suffers is structural deformation, energy loss, and shock. And just like the car smashing into the proverbial wall, the greater the velocity, the more devastating the effect. Now imagine that car after 4 million collisions, there will be obvious visual damage but also unseen systemic damage. We live dynamic lives and as such, suffer dynamic consequences. Those wear and tear consequences generate heat and promote malalignment, repetitive systemic micro trauma leading to instability, range of motion issues, soft tissue inflammation, and degenerative joint disease.

Unilateral balance and support, with increased pressure along the medial column indicating deforming arch forces. Image by Resilience.Code

Asymmetry X 3

Not to sour this soup further, but let’s add the bitter taste of another dirty truth: the foot is not a symmetrical object, medial to lateral, distal to proximal, and even side to side.

While standing, the center of mass runs along the midline of the body. Our hips, legs and feet are perfectly positioned to provide a balanced bilateral center of pressure (COP) to our center of mass (COM). If we transition to unilateral support as in the tree pose in yoga, measurements will show an increased firing of the core, all hip musculature, and lower leg muscles like the anterior tibialis.  In particular, the tibialis anterior struggles to maintain the medial longitudinal arch while trying to reconcile to COM and the COP on a foot with differing architectures, medial and lateral.

As we add motion and velocity while running, vertical and tensile forces increase. This is particularly problematic for runners because of the dynamic single limb stance time and the incongruity of COM and COP trying to reconcile impact on that 3-dimensional asymmetric foot, which is adaptively and morphologically different medially and laterally. All this while constantly and rapidly needing to change from an accommodating body at impact to a rigid lever for propulsion. It is elegant and problematic at the same time. Such force adaptation becomes even more problematic when you introduce multi-directional running and sprinting in sport.

Feet Are Not Identical

Whether walking, running, or moving obliquely, most people look down, see their feet, and assume they behave the same. But as professionals, we know feet are rarely equal, leading to more variability, yet another inconvenient truth. Just as most people have a dominant hand that is often more coordinated and/or stronger, we tend to have the effects of sidedness with feet too.

Biases, We All Have Them

Single leg exercises and dynamic athletic positions in sport and running incite great demands from muscles like the tibialis anterior. Image by Resilience.Code

As members of the performance enhancement, restoration of function and rehabilitative care communities, we have biases too. Physical therapists and chiropractors often have a top-down view while podiatrists tend to have a bottom-up view. It’s good to be aware of our biases and remember that they are not mutually exclusive.

If we look at this with an eye on the kinetic chain, the hips and knees affect the feet and ankles, but  the feet and ankles also affect the individual feet. For example, recently we were watching a lecture on rehabilitative strength training, jumping mechanics symmetry, and data capture status post-knee surgery. During the demonstration, the asymptomatic volunteer demonstrated a “leakage of force” during the exercise that could readily be explained by a top-down approach. However, as the group studied the case further, measured force comparisons showed the volunteer was pronated more on the left, which was confirmed by the medial position of red vertical force vector, extending from foot to the hip. Shortly after, a similar situation came up regarding asymmetric foot abduction, which may have been attributable to external hip rotation, or maybe it was an additional biomechanical abnormality. An easy way around these biases is to expand your history-taking and physical examination or refer to the appropriate specialist so you have a broad view and don’t get hung up by the dirty truth about our biases.

The 2 feet may look the same, even measure the same, but their biomechanical influences have been different so elements like strength and position will dictate that these feet will function differently. Image by Resilience.Code

If we are willing to make peace with the larger truth that running is a contact sport in which we are structurally and mechanically disadvantaged, we can then begin to look at individual elements, develop strategies, and create best practices for our running population.

  • Strategies to aid those who understand the mechanics and are still going to run and play sports as bipeds could include:
  • Strength and gait training (focus on core strengthening – defining core)
  • Visual coaching (spanning all components of the visual system)
  • Orthopedic limb length assessment/intervention
  • Orthotics and strapping
  • Manual therapy for bony alignment, joint mobilization and range of motion
  • Motor training
  • Neuro-performance
  • Data capture for progress and treatment adaptation and improvement
  • And the list goes on

These issues exist in walking but are exacerbated by running and all sports and sources of weight bearing exercise because of the increased forces and extended single-stance times. Image by Resilience.Code

Runners Gonna Run

Computer aided gait analysis displaying retrograde, less economical, motions of the foot’s center of pressure during stance. Image by Resilience.Code

To summarize this set of dirty truths surrounding anatomy and symmetry:

The foot is not symmetrical. Feet are rarely equal, thus introducing sidedness and strength from both the top down and the bottom up. Within normal limits does not equate to equality. Specialists all have biases with or without good medical history/trauma review.

When we introduce motion and single-stance phases in running and sport, we change and challenge the dynamic. A single foot on the ground upsets the balance between COM and COP, and so to compensate, forces the joints to leave neutrality and function in less advantageous alignments.

Perhaps the last and most enduring dirty truth is that people, if able, despite all the other dirty truths, are going to run.  Thus, we must accept the fact that we will do it as bipeds and have evolved this way, unlike bears.  Hopefully, this piece will bring some light, understanding, strategies, and reasonability to how providers care for us bipeds who choose to run.

Jay Segel, DPM, is consultant specializing in podiatric biomechanics, preventative and rehabilitative foot care. He practices in West Tisbury, Massachusetts, and is a consultat for Orthotic Holdings Inc.

Sally Crawford, MS, is Director of Technology & Data Management at Resilience Code, a data-driven medical solutions firm in Englewood, Colorado.

Grace Juriel is a podiatry student.

Jason Kraus is Managing Director and Founder of Starflower Row Advisors in Hauppauge, New York. He is the former President and Chief Operating Officer of Langer Biomechanics and has more than 20 years of experience leading medical device enterprises specializing in non-surgical lower extremity solutions.

Differences in force transitions explained by said “leakages of force” during concentric phases of vertical jump movements (last portion of the load phase in this image) require understanding the origin of deficits. Image by Resilience.Code

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