Recently I wrote about a possible connection between plantar fasciitis and hamstring tightness. Despite the high prevalence of plantar fasciitis and heel pain, there still remains a lot of mystery with regard to the actual cause of the condition and consequently the best method of treatment. Several risk factors, like inflexibility and obesity, have been identified and hopefully future research will shed light on the exact nature of the problem. In this post I’m going to discuss what I would consider to be another likely factor in the develoment of the injury: the toe spring.
Toe spring refers to the upward curvature at the end of the shoe near the toes. The toe spring allows for a rocking motion to occur as a way to compensate for the fact that the sole of the shoe is not capable of bending and flexing in the same manner as the foot. In a shoe with a very rigid sole, a toe spring is almost a necessity to prevent the shoe from drastically altering normal gait mechanics. Whether or not the curve is necessary in a flexible-soled shoe is debatable. Regardless of the flexibility of the shoe, a toe spring is going to hold the toes in an elevated position during standing and most of the gait cycle. This alteration in the position of the foot is why a case could be made for the toe spring causing plantar fasciitis.
The plantar fascia is a broad band of tissue that runs from the heel to the base of the five toes. The pain associated with plantar fasciitis typically occurs at the attachment point on the heel. When the toes are held in extension by a shoe’s toe spring, the plantar fascia is going to be under increased tension by way of the windlass mechanism. Increased tensile forces through the fascia is one theory on how the problem develops, so it seems possible that holding the fascia in an elongated position for prolonged period could have a similar effect.
The plantar fascia supports the longitudinal arch is part of the one of foot’s shock absorbing mechanisms. The fascia elongates when weight is transferred through the foot and springs back to it’s original length when force is removed. If the plantar fascia is already in an elongated position when the foot contacts the ground, how much more can it stretch? The additional tensile force applied with each step, in excess of what would occur when walking barefoot, is another mechanism by which the tissue could be damaged.
Directly above the plantar fascia on the underside the foot is the Flexor Digitorum Brevis (FDB) muscle. Like the fascia, this muscle spans the bottom of the foot from the heel to the toes, and consequently it too will be held in a stretched position when the foot is placed in a shoe with a toe spring. I would argue that this position effectively immobilizes the muscle by preventing it from contracting and shortening as it normally would when walking barefoot, when the toes firmly engage with the ground. Furthermore, if the FDB is unable to effectively contract and assist in stabilizing the arch, the plantar fascia may be forced to withstand additional stress to compensate which over time could lead to injury.
In order to heal properly, injured tissue requires a good blood supply. The positioning of the foot inside the shoe may compress blood vessels traveling along the bottom of the foot or disrupt blood flow to the heel. If the plantar fascia is getting injured on a daily basis, but is not receiving the circulation necessary to repair itself, this could lead to the degenerative changes often seen in the conidtion. It also seems plausible that if there is less muscle activity in the bottom of the foot due to the toes being splinted in a dorsiflexed position that this might cause an overall decrease in blood flow to the area.
So if the toe spring in footwear is the cause, or at least a contributing factor, in a subset of plantar fasciitis cases, how should we approach treatment of the condition? The most obvious solution for someone who suspects their footwear may be to blame would be to wear shoes with little to no toe spring and preferably a highly flexible sole. The next priority would be to engage in activity that would allow for the motions of the foot that are restricted by a toe spring, mainly toe flexion. This could include increasing barefoot activity and exercises that involve curling and gripping with the toes.
I frequently see stretching the plantar fascia recommended as a treatment for the condition. Even without considering the toe spring, I’m not sure that lengthening the fascia holds much therapeutic value. One of the reasons I think plantar fascia stretching is popular is because often the stretch will reproduce the pain in the heel which may make it seem like the exercise is being effective. Given that most footwear holds the plantar fascia in a lengthened position, I’m not sure what more can be accomplished by further tugging on the sensitive tissue. Stretches may be helpful if they increase movement, and circulation, in and around the fascia and muscles on the underside of the foot, or by adding stresses to the tissue that promote a healing response. Looking at this toe spring model, which again is just one theory of how plantar fasciitis might develop, it would make more sense to stretch the tissues on the top of the foot that are being held in a shortened position by the shoe rather than attempting that stretch the plantar fascia further.
The curved toe spring found in most running shoes holds the plantar fascia in a stretched position and is a possible contributing factor to the development of plantar fasciitis. The positioning of the foot inside a shoe with a pronounced toe spring may hinder shock absorption and muscle activity of the foot intrinsic muscles, thereby placing additional strain on the plantar fascia.
Toe spring is just one of the ways I think shoe construction might be a cause of plantar fasciitis. Other variables that might also be worth examining are the flex points of the sole, the overall flexibility of the shoe, the width of the toe box, the shape and positioning of any in-built arch support, heel height, and overall curvature. The actual cause of the plantar fasciitis may be multi-factorial, with footwear only being one variable in that equation. Moving forward toward effective treatment and prevention strategies involves identifying all possible risk factors, and I think a strong case can be made for the influence of footwear in the development of the condition.