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The Monday Shakeout: Challenges with Large Toe Spring Angles
By Matthew Klein

This week we talk about toe spring angles and some of the challenges associated with higher angles. Many people confuse toe spring, forefoot rockers and other terms that refer to the front of the shoe and how they may impact biomechanics of the foot, ankle and lower extremity. We hope to clear that up and help people figure out what will and will not work for them when it comes to the front of the shoe.


An area of the shoes we frequently focus on is the forefoot or front of the shoe. Besides being the place where the toes and front of the foot reside, it is an important place for either flexibility or an appropriate rocker to facilitate forward motion. With increasing stack heights, shoes have become more stiff, necessitating the need for rockers that allow for a smooth transition forward. A forefoot rocker refers to the upward curve in the midsole at the front of the shoe that imitates what would normally be the extension at the metatarsophalangeal joints (toe joints) that allows the body to pass over the front of the foot during the terminal stance and pre-swing phases of running gait. When executed correctly, this upward curve of the sole comes up to the level of the toes and stops, allowing the toes to stay in a neutral position.

The Positives of Toe Spring

We have discussed extensively the benefits of toe springs for those with certain pathologies that cause limited toe mobility or adequately compensate for the increasingly stiffer soles on the market (our own articles and an article I wrote for Runner's World). In previous posts, we have discussed how a forefoot rocker can influence the biomechanics of the lower extremity. If executed correctly, they can reduce plantar pressures (pressure on the sole of the foot), can shift load away from the foot, ankle and calf and redistribute it to the knee and hip (Ahmed et al., 2020; Sobhani et al,. 2016; Sobhani et al., 2017). This may be good for certain people looking to reduce the load at their calf and forefoot, but potentially problematic for those looking to shift load to those spots and away from others. A variation of this is called toe spring, where the midsole curve comes up so far it impacts the position of the toes, requiring them to be in additional extension. The angle that this keeps the toes at is referred to the toe spring angle.




Image from Bartold Clinical, which is a fantastic resource
What a Large Toe Spring Angle Does

Running requires at least 60-90 degrees of toe extension for normal mechanics. An appropriate forefoot rocker can compensate for this if someone is missing that motion. A large toe spring angle comes up so far that it holds the toes in extension without allowing them to flex. This tension on the toe flexors also tightens the plantarfascia and lifts the arch. This can naturally stiffen the foot, a normal part of the windlass mechanism of the foot the plantar fascia assists with. This is particularly important during the propulsive phase of gait where the foot needs to become a stiff platform for the body to push off. The challenge with this is that the foot also needs to be mobile during the landing phase for shock absorption.

Keeping it constantly stiff and locked up may limit the ability of the foot/ankle to shock absorb, increasing stress into a variety of structures. However, further evidence has found that toe spring may not increase stiffness in the arch as much as previously thought (Sichting et al., 2020). Another challenge comes from the fact that the toe flexors and plantar fascia are in a constant state of stretch. While stretching by itself is not a bad thing, constant stretch with load and without rest can become straining. This may result in tissue damage for those sensitive to it. Most tissues in the body are meant to go to into extremes of motion briefly then return to some variation of a neutral (middle) position (or close to it). Toe spring keeps the toes constantly in that position. This can also be problematic for those who do not have toe extension, such as those with hallux rigidus or a stiffening of the first toe joint. If they do not have any flexibility in that joint, a shoe with toe spring will not work given that their toes cannot achieve that motion either passively or actively.


Asics Glideride 3
Other Effects of Large Toe Spring Angles

A large toe spring angle can also change how people react to a shoe. The upward curve can functionally shorten the shoe if the angle is steep enough, causing people's toes to hit the superior aspect of the upper. This may require many individuals to go up a half-size to accommodate this, which may or may not work if the flex points of the forefoot are incorrectly offset. For those who choose not to change size, many people may compensate and functionally shorten their own foot by curling, flexing or "clawing" their toes to prevent them from hitting the end of the shoe. This now does the opposite of the above and puts the toe flexors and toe joints in an excessive, constant amount of flexion. This can shorten both the muscles and stiffen the joints, causing irritation/overworking of the active tissues (muscles) or shortening of the active and passive tissues. The human foot is meant to be able to move into and out of extremes of motion, not be held in them when also factoring in the shock absorption and propulsive requirements associated with running and gait.

Do I Need a High Toe Spring Shoe?

While some form of forefoot rocker is required for the increasingly taller and stiffer midsoles we are seeing on the market, how large a toe spring angle people will be able to tolerate will vary. It is a far safer option to have a low toe spring angle with a forefoot rocker as the toes typically do best in a neutral, middle position if they are to stay in one place for extended periods of time. Additionally, large toe spring angles can be problematic for those with arthritic toe joints or hallux rigidus (stiffening) or may predispose others to potential toe clawing.

Given that the toes work best being able to return to a neutral position and not being forcibly held at an end range, we generally suggest most people look for shoes with a low toe spring angle. There has NOT been extensive evidence linking a high toe spring angle to an increased risk of injury and our concerns come from basic biomechanics, kinesiology and clinical patterns.

So if a high toe spring angle works for you and you are not having problems, ignore this. However if you are experiencing any similar issues mentioned above in response to a high toe spring angle, this may be something you should consider avoiding. 


References

Ahmed, S., Barwick, A., Butterworth, P., & Nancarrow, S. (2020). Footwear and insole design features that reduce neuropathic plantar forefoot ulcer risk in people with diabetes: a systematic literature review. Journal of foot and ankle research13(1), 1-13.

Sichting, F., Holowka, N. B., Hansen, O. B., & Lieberman, D. E. (2020). Effect of the upward curvature of toe springs on walking biomechanics in humans. Scientific Reports10(1), 14643.

Sobhani, S., Heuvel, E., Dekker, R., Postema, K., Kluitenberg, B., Bredeweg, S., Hijmans, J.  (2017).  Biomechanics of running with rocker shoes.  
Journal of Science and Medicine in Sport.  20(1): 38-44.

Sobhani, S., Zwerver, J., Heuvel, E., Postema, K., Dekker, R., Hijmans, J.  (2013).  Rocker shoes reduce achilles tendon load in running and walking in patients with chronic achilles tendinopathy.  Journal of Science and Medicine in Sport.  http://dx.doi.org/10/1016/j.jsams.2014.02.008


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Phases of Running Gait

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