Director of the Center for Endurance Sports at the University of Virginia
Running in shoes is very different from running barefoot. High forces on the heel at contact don’t feel good. When barefoot, the runner figures out in a matter of strides that it is better to land with the foot somewhat flatter and closer to the body. While the intent of this gait modification was simply to lessen forces at the heel, it also completely changes the foot strike pattern, cadence, and the stiffness of the body. Other changes also occur in shod vs. unshod running, as you can see by the following study results from “The Effect of Running Shoes on Lower Extremity Joint Torques”:
1. Knee Flexion Torque: 36% increase in the knee flexion torque with running shoes potentially increases the work of the quadriceps, increases strain through the patella tendon, and increases pressure across the patellofemoral joint.
2. Knee Varus Torque: 38% increase in the knee varus torque with shoes implies relatively greater compressive loading on the medial tibiofemoral compartment, an anatomical site prone to degenerative joint changes, as compared to the lateral compartment.
3. Hip Internal Rotation Torque: 54% increase in the hip internal rotation torque may have particularly high clinical relevance given prior findings that indicate that competitive running may elevate the risk of osteoarthritis of the hip joint.
Although research can measure the above changes in the body, one thing that we are not able to look at is the amount of the compliance that occurs in the joint level while running shod vs. unshod. Technology does not yet exist to place a sensor inside the joint to measure actual compressive force that the joint experiences. Therefore, the effect of shoe construction on loads at the joint surface is not able to be measured at this time.
The soft materials in modern running shoes allow a contact style that you would not use barefoot. The foot no longer gets the proprioceptive cues that it gets unshod. The foot naturally accommodates to surfaces rapidly, but a midsole can impair the foot’s ability to react to the ground. This can mute or alter feedback the body gets while running. These factors allow a runner to adopt a gait that causes the elevated forces observed above.
Despite the data presented above, it is ridiculous to say that everyone should stop wearing shoes. Shoes are necessary for both protection and support in modern America. Running barefoot 100% of the time would require the vast majority of runners to restrict their training routes to avoid litter, debris, and numerous terrain surfaces. Cuts, scrapes, and bruises on the foot can prevent you from training altogether. The running shoe industry is trying to identify parameters in their shoes that encourage a more neutral running form, with less “intervention” from the shoe. New minimalist-design shoes are attempting to find the right balance for natural foot function and foot protection.
With this said, I think a certain amount of barefoot running each week is beneficial. This will train the body to adopt a more efficient running form. As Americans, our feet are weak compared to many other cultures that, from birth onward, spend considerable time without footwear. The volume of barefoot miles you can sustain is more individually based on how your foot structure developed. Some foot structure types will be able to adopt barefoot running rather easily. Other runners will need to strengthen their feet considerably before they are able to sustain a given amount of barefoot mileage without injury. Having a weak foot is not a sign that you’re a poor runner, it’s simply pointing out a weakness. Feet strengthening and barefoot running are a great way to train your weakness and become one step closer to a well rounded athlete.