Footwear Science: Toe Spring

   Today we discuss something that I bring up frequently in my footwear posts: Toe Spring.  Toe spring is the rise or curve upward of the sole at the forefoot.  The reasoning behind it is to smooth out the toe off or terminal stance/pre-swing phase of gait as the runner transitions over their metatarsophalangeal joints (most proximal joints of your toes) aka your forefoot (part of it).

Image via Pace Athletic

   This feature of running shoes is commonly used to help roll the foot forward during the end of the stance phase of gait, especially in shoes that tend to be stiff or lack flexibility through the forefoot.  This stiffness can come from a variety of sources.  It can be utilized in overly thick midsoles, common in many of the max cushioned shoes that have been popular recently, especially Hoka One One.  Due to their increased thickness, they tend to have less flex and bend to them.  


An example of the toespring used in Hoka Shoes.  Image via: Running Warehouse Blog

     Toe spring can also be utilized in shoes with very stiff soles, such as racing shoes with plastic, pebax or carbon fiber plates to aide in propulsion.  A great example of this is the older non-boosted Adidas Adios models with their extended forefoot torsion system.  While this helped make the shoe fast and acted like a lever to increase the torque during toe-off, it definitely made the forefoot very stiff.  Without the toespring, attempting to roll off the forefoot would have felt even more stiff.

  
Image via Wiggle UK

   The theoretical biomechanical reasoning behind toe spring has to do with the last rocker of the foot.  I have discussed the rockers of the foot in prior footwear reviews (and it will definitely show up again).  The rockers of the foot aide in efficiency of gait and maintence of forward momentum.  The heel rocker is the first, which upon heel contact helps roll the foot forward.  The ankle rocker is second and involves the tibia/fibula rolling over the foot (at the talocrural joint).  Finally we have the forefoot rocker, which continues to maintain forward momentum by allowing the body to roll over the metatarsophalangeal joints.  These all can occur without additional muscular forces and thanks to the rolling/rocker effects, preserve energy.  If the body had to go over sharp jarring edges, the muscles of the lower leg and foot would have to work much harder to pull and push the body forward.  While these are partially passive in nature, they can be influenced by muscles.  If the calves are too tight for example, the ankle rocker can be inhibited due to running out of muscle length before the tibia/fibula can translate over the foot.  The same applies to the forefoot rocker.  If someone lacks MTP extension, especially great toe extension, then instead of being able to nicely roll over than forefoot, the individual will have to work extra hard to roll over the end of the toes (excessive strain on the calves) or they will roll off the medial or inner side of the big to. This places excessive pressure on that aspect of the bone and over many years can cause a bony grow most people refer to as bunions.  As I always tell my patients, these things usually happen for a reason and don't just come out of nowhere.  For normal gait, you need about 60-65 degrees of great toe extension.  Those with tight calves, weak and tight feet will not have that.  Hence why so many people have bunions!  


Image via Freelap USA

    A quick scan of the internet reveals fairly negative feelings regarding toe-spring.  Several websites laud this aspect of the shoe as a "foot deforming" design and generally seem to push toward this feature causing plantar fasciitis and/or hammer toes.  A quick review of the literature reveals no evidence that there is a direct link between plantar fasciitis and toe spring.  Many individuals and clinicians may have testimonial evidence, but that always needs to be taken with a grain of salt.  Could this cause plantar fasciitis or hammer toes?  Maybe.  I can see from a biomechanically argument that if the toes are forced into an amount of extension they don't normally have, that could place additional stress on the plantar muscles and ligaments of the foot.  In the case of hammer toes, excessive upward curve of the front of the shoe can functionally shorten the shoe.  To compensate for that lack of length or lack of metatarsophalangeal extension, the toes can curl to shorten foot length and avoid being placed in that position.  Do I see this in some runners who wear shoes with excessive toe spring?  I certainly have.  Is there research backing this?  Not that I am aware of (if you are aware of some please let me know).  So due to human variability, some people may be able to get around this due to flexibility, while others that lack mobility may not.  

Airia 1.5 Men
Holy Toe Spring Batman!!!  Image via Airia Running

    While I have also had fairly negative feelings toward excessive toe spring, like anything in life, there has to be a balance.  With shoes with stiffer forefoots, a certain degree of toe spring is needed to reduce strain on the calves and plantar ligaments/muscles as the body attempts to get over a disabled forefoot rocker.  With individuals that lack metarasophalangeal extension (common with foot osteoarthritis and a variety of other condition), toe spring creates and artificial forefoot rocker for these individuals, who would otherwise compensate and place excess stress on other parts of their bodies.  So I see toe spring as a tool that some individuals or shoes may need.  Like any aspect of footwear design, balance is key.  I would much rather see a more flexible forefoot to allow the toes to dorsiflex and allow the body to naturally transition over the front of the foot/shoe.  With certain racing shoes and maximalist shoes, that may not be possible.

    Will toe spring make you faster?  More than likely, no.  It is simply a way to artificially replace a biomechanical feature of the foot.  For people that lack that feature, this is something you should look for.  For everyone else, I suggest finding the shoe with the least amount of toe spring possible and instead working on the strength of your ankle and toe dorsiflexors and the length of your ankle and foot flexors (especially your calves).  As mentioned earlier, you need at least 60 degrees of great toe extension for normal gait.  If you are wondering why your calves are tight, maybe you you take a look at working on that (there will be a future post on this).

Thanks for reading.

*As always, my views are my own.  My blog should not and does not serve as a replacement for seeking professional medical care.  I have not evaluated you in person, am not aware of your injury history and personal biomechanics, thus am not responsible for any injury that you may incur from the performance of the exercises on this blog.  This blog is meant for educational purposes only.  If you are currently injured or concerned about an injury, please see your local physical therapist.

Dr. Matthew Klein, PT, DPT
Casa Colina Orthopedic Resident

References

Neumann, D. (2012).  Kinesiology of the Musculoskeletal System: Foundations for Rehabilitation - Second Edition.  St. Louis, MI: Mosby Elsevier

Noakes, T. (2003). Lore of Running - Fourth Edition. Champaign, Il: Human Kinetics

Perry, J. (1992). Gait Analysis: Normal and Pathological Function. Thorafare, NJ: SLACK Incorporated.

Comments

  1. Am curious - if shoes have equal toe spring but one has a much higher heel (say 4mm and 10m drop), does the 4mm drop have a larger functional toespring?

    From personal experience, I can say that when the muscles around the ankle and calves are tighter, a greater toespring causes me more trouble.

    ReplyDelete
    Replies
    1. I have no research to back up this comment, but I would think that a higher drop would have a larger functional toe spring to the foot being angled higher (toes held in great extension). Whereas with a lower drop, since the heel is lower, the functional toe spring would be less.

      And I agree that there are some muscles of the ankle and calves that may get tighter with toe spring. The peroneus longus (starts on lateral aspect of fibula and goes all the way to the first toe) can have some issue since toe spring can force the first MTP joint down and keeps the PL in a shortened position.... which could be good or bad depending on your mechanics. If the toe spring is excessive, this can lead to toe curling, which tightens the toe and foot flexors, which can play pressure on the plantar fascia or calf/tibial muscles. So as always, some people will do well, others will not.

      Thanks for the comment and hope that helps. No research currently on that and just thinking from a physics standpoint. I might be wrong so if you figure out otherwise please post!

      -Dr. Matthew Klein, PT, DPT

      Delete
  2. I completely agree with you. The best shoes for flat feet are made considering all these points and it's really good.

    ReplyDelete
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