Running related injuries are at an all-time high because of shoes!

With injury plaguing our most primal form of locomotion, let’s see if the scientific literature can explain why.

From an evolutionary standpoint, we are built to run and have done so for thousands of years [1]. Traveling long distances while using the least amount of energy and staying injury free was crucial to the survival of our species. So if these traits are innate, then why do 19.4- 79.3% of recreational runners end up injured within one year of running [9]?

From a biomechanical standpoint, the most efficient movement is also the most preserving on its structures. So let’s dissect the way people run and see if any inefficiencies exist.

It is pointless to describe the running motion, as, everyone should have a pretty clear image in their heads. Let’s, however, hone in on the stage where the foot comes into contact with the ground. This part of the gait cycle has the highest forces acting on runner’s physical tissues and thus holds significance in the investigation.

There are three ways that the foot comes into contact with the ground.

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Heel/Rearfoot Strike (RFS): Heel comes in contact with the ground first at impact.
Mid-foot Strike (MFS): Middle foot comes in contact with the ground first at impact.
Forefoot Strike (FFS): Front foot makes contact with the ground first at impact.

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A whopping 72-89% of runners RFS [7].

The human being has evolved to strike the ground with their mid-foot or front-foot [1]. The catalyst for high rates of heel striking is modern footwear [2][8].

Think about landing on your heels barefoot. You would feel an immediate pain shoot through your legs and into your back. The signals come from our sensory feedback mechanism which prompts us to change our movement pattern [8].

During a 12 week study, participants had to implement an increasing amount of barefoot running into their weekly training. The results showed a 90% change in running style, favoring a more forward foot strike.[6][4]

Let’s analyze the biomechanics of Barefoot running compared to shod (shoe running) and see if we can identify mechanisms for injury.

Step/Stride length and cadence

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Step length: Distance between ground contact of the opposite legs
Stride length: Distance between ground contact of the same legs [5].

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Efficiency

Running barefoot shortens both the step and stride lengths, which in turn increases cadence [2]. A higher cadence rate is said to conserve forward momentum [2]. This energy efficiency makes sense when we analyze foot position in relation to the center of gravity.

Centre of gravity, braking forces and Stance time

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Ground reaction force (GRF): The force exerted by the earth on the body at contact [13]
Leg stiffness: The level of resistance in the leg at impact [4]
Stance time: The duration from initial contact to lift off of the foot [5]
Impulse: Force x Time

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Efficiency

In this illustration, you can see the result of a lengthened stride length. The shod runner’s striking leg is so far ahead of his center of mass that he applies braking forces every time he lands.

The ground reaction forces imparted on heel strikers is up to 3x times higher than a M/FFS [6]. The high forces travel up the stance leg, into the hip and cause flexion (as seen by the torso moving forward). This upstream movement causes the runner’s center of mass to shift even further back and slow him down more [8].

Injury

Shoe runners have an increased stance time compared to BF [4]. The extra time that the foot spends in contact with the ground increases the impulse which results in higher Peak GRF in the knee joint. The runner's feet should feel the high forces and try to disperse them through a relaxed leg. Unfortunately, the use of cushioned shoes curb that sensory feedback mechanism, and the athlete ends up stiffening the leg more [4]. It is the combination of high muscle contractile forces and high ground forces that can overload the knee joint and potentially cause injury [11].

Dorsiflexion and Plantar flexion

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Dorsiflexion: Toes move toward shin bone
Plantar flexion: Toes move away from shin bone

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Efficiency

The shod runner strikes the ground with a dorsiflexed foot position, utilizing the anterior (front) muscles of the shin bone. The barefoot runner hits the ground in a plantar flexed foot position which engages the posterior (back) tendon and muscles. The Achilles is the strongest tendon in the human body, which helps propel the athlete using its high stretch reflex capability [3]. You could think of this connective tissue as a spring. Connected to the Achilles tendon is the Soleus muscle, made up of slow twitch muscle fibers. The properties of this muscle make it very enduring and resistant to fatigue [3].

Injury

Dr. John Anderson, a physiology researcher, explained how the extra stress on the Tibialis anterior muscles of the shod runner is one of the leading contributors to shin splints today [14]. Similar statements were made in the Journal of Gait and Posture [7]. Through observation of the illustration above, it is clear that the sheer size of the posterior structures makes them more capable of handling the forces of impact.

Pronation and Knee Valgus

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Pronation- Rolling of the foot from lateral (out) to medial (in).
Knee Valgus- Knee moves towards the midline.

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Efficiency

Through the adoption of a MFS/FFS patterns of barefoot runners, the underfoot muscles are engaged to exert more thrust force through a recoil action [15]. Recruitment of these muscles happen via the enhanced sensory feedback mechanism (the ability to feel the ground at impact) [8]. On the contrary, shod runners lose this benefit because of their lack of feeling.

Injury

The use of shoes and arch support, while running, weaken the stabilizing muscles of the foot [15]. An unstable foot coupled with higher peak GRF, the shod runner excessively pronates during impact and liftoff. The model on the right shows how dormant short springs (representing the fast reacting muscles of the foot) render it helpless in the stabilisation of the ankle during high impact phases of running [1].

Excessive pronation loads the tissues of the ankle joints and collapses the arch as seen in the illustration above. Collapsing of the arch has been found to be a mechanism for plantar fasciitis syndrome. The effects move upstream by rotating the shinbone, forcing the knee joint medially (towards the midline) into a valgus position. The internal rotation has a further impact on the hip, pulling it out of alignment. This cascade of events explains the many ACL tears and lumbar injuries in so many runners [11] [16] [9].

Conclusion

Since the advent of running shoes in the 1970’s and their many technological advancements since then, it is clear that we have benefited very little from them [11]. Even though the shoe companies may not have had the intention of hurting millions of people, they have ended up doing so by changing the way people run [10].

Don’t try to fix something that is not broken. Divine creation/millions of years of evolution have equipped us with all the robust structures needed for basic locomotion. We don’t need your $150 pair of kicks.

It is not a coincidence that the Kenyan runners of the Rift Valley province, famous for their endurance running, grew up barefoot [11].

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Sources

*All images were created by Exercising Health

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