Achilles tendonitis: Lift the heel, right? It does not appear so.

There was a recent article in one of our favorite journals, Lower Extremity Review which reviewed and expanded on another study from Medicine and Science in Sports and Exercise we spoke about several PODcasts ago titled “Running shoes increase achilles tendon load in walking: an acoustic propagation study.”

 

The article discusses a new technique (1,2) for looking at tensile loads in the achilles and looks at 12 symptom free individuals on a treadmill barefoot and in a shoe with a 10 mm drop and found:

“Footwear resulted in a significant increase in step length, stance duration, and peak vertical ground reaction force compared with barefoot walking. Peak acoustic velocity in the Achilles tendon (P1, P2) was significantly higher with running shoes.”(1)

 

According to LER: “The researchers also found changes in basic gait parameters associated with walking in running shoes versus barefoot, which Wearing said may help explain the increased tendon load with shoes. Shoes increased mean ankle plantar flexion by 4° during quiet stance as measured by electrogoniometry. When walking with shoes, participants adopted a lower step frequency but greater step length, period of double support, peak vertical ground reaction force, and loading rate than when walking barefoot. The researchers also noted that participants’ stance phase was relatively longer (4%) during shod walking than during barefoot walking.” (3)

 

Of course, our big question is why?

 

Would an increase in step length result in increased tension? Perhaps, as the force that the heel would hit the ground would be increased because of a longer acceleration time (F=ma) and that is also what they found. The friction of the heel striking the ground would accelerate anterior translation of the talus, which plantar flexes, everts and abducts, accelerating pronation. The medial gastroc would be called into play to slow calcaneal eversion and this would indeed increase achilles tension.

 

Or perhaps it’s the fact that the foot will strike in slight greater plantarflexion (at least 4 degrees according to the study) and this results in an immediate greater load to the Achilles tendon.  Go ahead and try this while walking even if you’re barefoot. Walk across the floor and strike more on your forefoot. You will notice that you have an increased load in the tricep surae group.

 

Does this slight plantarflexion of the ankle contribute to greater eccentric load during stance phase?  This would certainly activate Ia afferent muscle spindles which would increase tensile stresses in the Achilles tendon.

 

This seems to fly directly in the face of the findings of Sinclair (4) who investigated knee and ankle loading in barefoot and barefoot inspired footwear and found increased Achilles loading in both compared to “conventional shoes”.

 

Of course this also begs the question of  what type of shoes were they in? High top shoes or low top shoes and were the shoes tied or not? High top shoes seem to reduce Achilles tension more so than low top shoes, especially if they are tied (5).

 

 Whatever the reason, this questions the use of putting a lift or a higher heel shoe underneath the foot of people that have Achilles tendinitis.  Once again what seemed to make biomechanical sense is trumped by science.

 

 We think training people to have greater amounts of hip extension as well as ankle dorsiflexion,  as well as appropriate foot and lower extremity biomechanics with the requisite  skill, endurance and strength is a much better way to treat Achilles tendonitis regardless of whether they’re wearing footwear or not.

 

The Gait Guys

 

References:

1. Wearing SC, Reed LF, Hooper SL, et al. Running shoes increase Achilles tendon load in walking: An acoustic propagation study. Med Sci Sports Exerc 2014;46(8):1604-1609.  http://www.ncbi.nlm.nih.gov/pubmed/24500535

2. Reed LF, Urry SR, Wearing SC. Reliability of spatiotemporal and kinetic gait parameters determined by a new instrumented treadmill system. BMC Musculoskelet Disord 2013;14:249.

3. Black, Hank. Achilles oddity: Heeled shoes may boost load during gait. In the Moment:Rehabilitation   LER Sept 2014  http://lermagazine.com/news/in-the-moment-rehabilitation/achilles-oddity-heeled-shoes-may-boost-load-during-gait

4. Sinclair J. Effects of barefoot and barefoot inspired footwear on knee and ankle loading during running. Clin Biomech (Bristol, Avon). 2014 Apr;29(4):395-9. doi: 10.1016/j.clinbiomech.2014.02.004. Epub 2014 Feb 23.

5. Rowson S1, McNally C, Duma SM. Can footwear affect achilles tendon loading? Clin J Sport Med. 2010 Sep;20(5):344-9. doi: 10.1097/JSM.0b013e3181ed7e50.

Proprioception trumps Biomechanics

As I sit here on a rare Friday afternoon, not working (OK, I am writing this, so sort of working) and looking out at the lake (picture above), while on a family camping trip, I think about a walk on the rocks this morning with my kids. I was watching my very skilled 7 year old jump from rock to rock while my 3 1/2 year old, that thinks he is seven, tried to follow his older brother.

I had my foot on a rock which lowered the front of my foot in plantar flexion and stood on that leg. I noticed that my balance was not as great as it was when my foot was in dorsiflexion. This made me think about pronation and supination. Yes, it is not uncommon for me to think about such things, especially when I have some spare time. That is one of the things about being a foot and gait nerd; these sorts of things are always on our minds.

So, why was my balance off? Did I need more proprioceptive work? Were my foot intrinsics having issues? No, it was something much more mundane.

Pronation consists of dorsiflexion, eversion and abduction. This places the foot in a  “mobile adaptor” posture, reminiscent of our hunter/gatherer ancestors, who needed to adapt to uneven surfaces while walking over terra firma barefoot. Supination, on the other hand (which is the position my foot was in), consists of plantarflexion, inversion and adduction. It places the foot (particularly the midtarsals) in a locked position for propulsion (think of the foot position during toe off).

So why when my foot was plantar flexed and adducted while standing on this rock so much more unstable in this supposedly more stable, supinated position? I would encourage you, at this point, to try this so you can see what I mean. When I placed my foot in dorsiflexion on the rock, I was much more stable. A most interesting conundrum for a biomechanist.

Experimenting for a few minutes, alternating plantar flexion and dorsi flexion, gave me the answer. When we are walking on the flats, our foot is (usually) not pushed to the extremes of dorsiflexion; with the front of the foot up on a rock, it is much more so. This “extra” upward force on the front of the foot, provides much more sensory input (and thus proprioception) from the ball of the feet. Take a look at the sensory homunculus and you can see how much brain real estate is dedicated to your foot, especially the front portion. With this information, we are able to apply more  force through the posterior compartment of the leg,which is stronger than my anterior compartment (as it is with most folks).

When the front of your foot is in plantar flexion (ie, your heel is on the rock), we have less sensory input to the balls of the feet, and rely more on the anterior compartment (weaker in many folks, including myself) to counterbalance the weight of our body.

Mystery solved: proprioception trumps biomechanics; more proof that the brain is smarter than we are.

The Gait Guys. Solving the worlds great gait questions, one at a time.