How do carbon fiber insoles affect gait?
Part 2 - rocker mechanics of the lower extremity
Rockers are a very important part of lower extremity biomechanics. Rockers describe pivot points in the gait cycle that decrease the range of motion of the ankle and knee. Rockers are also employed by the body to conserve energy during gait. In the lower extremity, the three rockers are the heel rocker (also called a rearfoot rocker), the ankle and the forefoot rocker. What’s the importance of each of these rockers? Let’s take a closer look.
Rearfoot, ankle and forefoot rockers
The first image (below left) shows the function of the foot without the ankle rocker. This image shows the excursion of the tibia using only the rearfoot and forefoot rocker. The total excursion of the tibia with just the rearfoot and forefoot rocker is significant resulting in what would be impractical range of motion of the knee. The second image (below right) adds a third rocker, the ankle rocker. Adding the ankle rocker significantly decreases the total excursion of the tibia which in turn decreases energy expended by the body during gait. In the second image, you can see that walking is a kinetic chain of events that relies on the interplay of multiple rockers. (Images from Human Walking by Inman, et al.)
How do carbon fiber inserts affect gait?
How do carbon fiber insoles affect rocker mechanics of the lower extremity? Rearfoot rocker mechanics aren’t affected in the least by rigid, carbon fiber insoles. Knowing from the images in this post that the forefoot rocker and ankle rocker work together, we can assume that any impact on the forefoot rocker will affect the ankle rocker. Use of most carbon fiber inserts is going to delay the toe-off phase of gait. This means that the Flat Shoe Plate, Molded Turf Toe Plate, and Flat Turf Toe Plates are all going to delay toe-off. To a degree, delay in toe-off will increase load to the lower back due to lifting of the foot instead of active toe-off. The Spring Plate, on the other hand, is just a bit different. Due to the built-in toe spring in the Spring Plate, the Spring Plate will allow for timely toe-off during gait.
If a carbon fiber insert affects the forefoot rocker, is that necessarily a bad thing? In most cases, no. Most users of carbon fiber plates really don’t notice the difference in their gait. For those with a history of lumbar pain though, the Spring Plate may be the better choice.