The modern running shoe was developed in the 1970s with the aim of cushioning the foot and protecting it from large impact forces that are encountered during running. However, with up to 70% of runners reporting an injury in any given year, research examining the impact of running shoes on feet is pretty important; not only for the health of a runner’s foot, but also for the development of improved footwear. New work published this month in Journal of the Royal Society Interface suggests that running shoes do indeed influence the mechanical function of the foot. We spoke to lead author Dr Luke Kelly.
How are shoes thought to impede running?
Most of this speculation arises from the fact that running injury rates have not declined over the last 40 years, despite the mass adoption of running shoes. From an evolutionary biologist’s perspective, humans have been running for millions of years and have not done so with cushioned running shoes.
The human foot functions like a spring when running. In the period immediately following contact of the foot with the ground, the arch of the foot becomes lower. This lowering of the arch (like compression of a spring) stretches the muscles and tendons located in the arch of the foot (like a rubber band) and allows some of the mechanical energy associated with foot ground impact to be temporarily stored in the stretched ligaments and tendons of the foot. This energy is returned during propulsion to help accelerate the body forward. This mechanism is analogous to a rubber band being stretched and subsequently released to sail across the room, providing considerable energy savings in running.
It has been suggested that running shoes may actually impair this function, with a thick cushioned running shoe impeding sensory feedback and the natural spring-like function of the arch. It has also been suggested that these changes in running mechanics may reduce the contribution from our muscles and tendons in storing and returning mechanical energy, leading to weakness, with these adaptations actually increasing the risk of injury to a runner.
What did you find out?
This study addresses the speculation pertaining to how running shoes influence the mechanical function of the feet and also how the brain and spinal cord controls the function of a group of muscles in the feet that support the arch, known collectively as the intrinsic foot muscles.
We found that running shoes do influence the spring-like function of the foot. When our participants ran in shoes they displayed substantially less lowering of the arch, suggesting that their feet were stiffer when running in shoes. This finding is in line with previous suggestions that running shoes may limit the spring like function of the foot due to their inherent cushioning and support features.
However, of significant novelty and importance is the associated finding that our participants actually activated (contracted) the muscles located within the arch of the foot more when they were running in shoes. Our previous investigations into the function of the intrinsic foot muscles inform us that these muscles stiffen the arch when they contract. Therefore, an increase in activation (or contraction) of these muscles when running in shoes suggests it is actually an increase in muscle activation that is responsible for the altered function of the arch, rather than the structural features and cushioning of the shoe.
Although this study did not directly examine the effect of running shoes on muscle strength, our findings suggest that running shoes do not impair muscle function and therefore it is unlikely that running shoes will cause muscle weakness.
This study incorporated a number of different research tools that give us a comprehensive and unique insight into the bio-mechanical function of the foot.
We used three-dimensional motion analysis, which involves the use of high-speed, infra-red cameras to track the movement of a number of small reflective markers that are placed on key anatomical landmarks of the leg and foot. The three-dimensional co-ordinates of these markers are then used within a computer software program to produce a geometrical model of the leg and foot in running.
Our participants ran on a treadmill that has two force plates built into the frame, allowing us to measure the forces generated by each runner during the experimental trials.
In order to record the activation patterns of the muscles located in the arch of the foot we used a technique known as intramuscular electromyography. This technique involves insertion of fine wire electrodes into the muscle tissue of each muscle. We use ultrasound imaging to find the correct muscle and then use a hypodermic needle (the electrodes are threaded through the hypodermic needle) to guide the electrodes into the muscle tissue while visualizing the needle under ultrasound.
Once the electrodes are in the correct position, the hypodermic needle is removed, leaving the fine wire electrodes in the muscle. The electrodes are subsequently connected to an acquisition system, allowing activation patterns to be recorded on a computer during running. The electrodes are very thin, approximately the width of a hair on your leg, and are generally not noticed by the participants when running. They are removed painlessly following completion of the experiments.
What’s better: barefoot for shod?
I don’t think we can directly answer this question, based on the findings from our study. Common sense suggests that running shoes provide a runner with protection from environmental dangers (broken glass, needles, excessive cold, etc.) and therefore they are important.
What the findings from our study do tell us is that running shoes do not stop the muscles in our feet and legs from doing their job, therefore it is unlikely that running shoes will create weak and lazy feet, as suggested by a number of people in scientific and popular media. What our research clearly says, is that shoes are not necessarily detrimental to muscle function in the foot and may actually (perhaps counter-intuitively) require our muscles to work harder than in barefoot conditions.
To whom might this study be important to?
Evolutionary biologists, sport scientists and clinical scientists, mostly, but it will also be of interest to people in the wider running community who have followed the scientific and social commentary surrounding the barefoot running debate over the past few years. These latest findings highlight the potential to tune the characteristics of running shoes to optimize the mechanical function of feet. There is now a great deal of potential to explore these concepts and with emerging manufacturing techniques, it may be possible in the future to customize the mechanical features of running shoes to individual feet.
Luke is an NHMRC Early Career Research Fellow within the Centre for Sensorimotor Performance in the School of Human Movement & Nutrition Sciences, The University of Queensland.
His research examines how the brain and spinal cord integrate sensory feedback to adapt the mechanical function of the foot during locomotion.