The Monday Shakeout: Hallux Mobility and Forefoot Rockers
By Matthew Klein
In this week's Monday Shakeout, Matt talks all about shoe characteristics for those with limited toe mobility.
We often talk about the rear part of the shoe, specifically heel bevels and their design, in reference to the landing phase of gait that many, but not all runners go through. I thought it might be nice to go to the other end of the shoe and talk about something that all runners experience regardless of footstrike - the transition off the forefoot. In biomechanical terms, this phase of gait is called the terminal stance/pre-swing or the push-off phase of gait. Much of the maximal force produced by the calves actually occurs prior to this and the primary activity is the transition over the forefoot and extension of the toes. The big toe joint or 1st Metatarsophalangeal (MTP) joint in particular is an important pivot point during this phase. Normal range of motion required for normal walking is about 60 degrees of toe extension at this joint, whereas running can require upwards of 90 degrees (Neumann, 2016). The motion here allows the body to transition across the front of the foot and in conjunction with the plantar fascia and long toe tendons allows the body to efficiently progress forward.
What Does a Forefoot Rocker Do?
This mechanism of rolling over the front of the foot is called the forefoot rocker as the body is able to rock forward over this (these if you include the other toes) joint which reduces the work the gastrocsoleus and plantarflexors need to do to maintain forward momentum.
As soles have gotten thicker and stiffer, a replacement is necessary to maintain this forward motion. Normally with thinner-soled shoes, the midsole at the front of the foot would naturally flex to allow this motion to still occur. Thicker midsoles and those with plates drastically reduce the flexibility and may prevent this motion. What is required to maintain it is an upward curve at the front of the sole called a forefoot rocker. Without allowing the sole to flex, this allows the foot to pivot forward along this curve to allow forward motion. This is slightly different from toe spring, which is the continuation of this curve upward that alters the resting position of the toes into extension. The apex of the rocker, or how early it begins, can affect when a person begins to roll forward, how quickly they will roll forward and how much stiffness is maintained (Chen et al., 2022).
How Those with Limited Great Toe Mobility Benefits from Forefoot Rockers
Those who have limited great toe or general toe mobility may benefit from a shoe with a significant, early-starting forefoot rocker. There is evidence that this design can improve the forward transition in those with hallux rigidus, bunions, plantar pressure sores and can even reduce load/tension on the Achilles tendon and calf muscles (Colo et al., 2020; Sobhani et al., 2015). The more severe the issues, the more benefit is gained from having the forefoot rocker begin earlier in the shoe. This begins the forward transition quicker, reducing the work and stress at the forefoot (Chen et al., 2022). On the contrary, the later the rocker is placed, the greater stress and stiffness may occur. The later may be good for faster runners who want that stiffness over shorter distances but may not work as well for those who want a smooth transition with reduced load at the front of the foot.
Picking a shoe with a comfortable forefoot transition is incredibly important. Bishop et al.'s (2020) RUN-CAT has found that one of the five most important factors in determining whether a shoe will work for someone is how comfortable the forefoot transition/flexibility is. This is not something that will be consistent across people as each will have different biomechanics, preferences and purposes for the shoe. However, for those with limited toe mobility, forefoot problems or irritated Achilles calves, a shoe with an early starting and large forefoot rocker may be beneficial. That force has to go somewhere and forefoot rockers have been found to increase load and activity at the muscles of the knee and hip (Sobhani et al., 2017), so those who have stronger hips may benefit from using this shoe type while those with weakness up there may not do as well. Loads are only shifted, so make sure you can handle them wherever they are sent.
References
Bishop, C., Buckley, J. D., Esterman, A. E., & Arnold, J. B. (2020). The running shoe comfort assessment tool (RUN-CAT): Development and evaluation of a new multi-item assessment tool for evaluating the comfort of running footwear. Journal of Sports Sciences, 38(18), 2100-2107.
Chen, T. L. W., Wong, D. W. C., Peng, Y., Wang, Y., Wong, I. K. K., Lam, T. K., ... & Zhang, M. (2022). The interaction effects of rocker angle and apex location in rocker shoe design on foot biomechanics and Achilles tendon loading. Medicine in Novel Technology and Devices, 13, 100111.
Colò, G., Fusini, F., Samaila, E. M., Rava, A., Felli, L., Alessio-Mazzola, M., & Magnan, B. (2020). The efficacy of shoe modifications and foot orthoses in treating patients with hallux rigidus: a comprehensive review of literature. Acta Bio Medica: Atenei Parmensis, 91(Suppl 14).
Neumann, D. A. (2016). Kinesiology of the musculoskeletal system-e-book: foundations for rehabilitation. Elsevier Health Sciences.
Sobhani, S., van den Heuvel, E. R., Dekker, R., Postema, K., Kluitenberg, B., Bredeweg, S. W., & Hijmans, J. M. (2017). Biomechanics of running with rocker shoes. Journal of Science and Medicine in Sport, 20(1), 38-44.
Sobhani, S., Zwerver, J., van den Heuvel, E., Postema, K., Dekker, R., & Hijmans, J. M. (2015). Rocker shoes reduce Achilles tendon load in running and walking in patients with chronic Achilles tendinopathy. Journal of Science and Medicine in Sport, 18(2), 133-138.
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