Marathon running and long-distance running in general are associated with a high risk of musculoskeletal injuries.
The foot, in particular, is prone to various running-related injuries.
For example, according to research that evaluated the incidence of musculoskeletal injuries in runners, somewhere between 5.7% to 39.3% of runners experience a foot injury over the course of the year while training.
Although some common foot injuries in runners are bony in nature, such as metatarsal stress fractures or stress fractures in other bones of the foot, or may involve other connective tissues such as the plantar fascia, it is also common for runners to experience injuries to foot muscles.
When considering the muscles of the foot, there are two general categories: extrinsic foot muscles and intrinsic foot muscles.
Extrinsic foot muscle groups are those that have their origin or somewhere up the leg. This means that the muscle is attached at its origin, or starting point, somewhere in the shin or ankle, and then the muscle belly and/or tenderness junction at the insertion point (bottom or far end of the muscle) is down in the foot.
Intrinsic muscles both originate and insert in the foot itself, which means that nope part of the muscle extends into the ankle or leg.
Together, the intrinsic and extrinsic muscles of the foot help support and control the mediolateral arch of the foot and will help flex and extend the toes.
Previous research has found that runners often exhibit a somewhat collapsed arch, or flat-footedness, particularly after running a marathon or due to chronic high-volume training.
A recent study published in the Scandinavian Journal of Medicine & Science in Sports aimed to look at the potential effects of marathon running on the health and function of the extrinsic vs intrinsic foot muscles.
The researchers were primarily interested in investigating whether marathon running caused more damage to the extrinsic foot muscles or internal foot muscles in terms of the functional ability of these muscle groups to help support and stabilize the arch of the foot.
To do so, the researchers recruited a study group composed of 22 collegiate runners.
Magnetic resonance imaging (MRI) Images of the feet were taken before running a full marathon, as well as one day after the marathon, three days after the marathon, and eight days after finishing the marathon.
Additionally, 10 of the 22 runners in the study also had a three-dimensional foot posture obtained using a foot scanner system before running the marathon as well as 1, 3, and 8 days after the marathon.
The researchers of the study looked at specific foot muscles including the following:
- Abductor hallucis, which is an intrinsic foot muscle that helps move the big toe inward towards your other foot.
- Quadratus plantae muscle, which is a deep-lying intrinsic foot muscle that helps flex the four toes other than the big toe.
- Flexor digitorum longus muscle, which is an extrinsic muscle of the foot that helps flex the toes aside from the big toe.
- Flexor hallucis longus, which is an extrinsic foot muscle that flexes the big toe only
- Flexor digitorum brevis, which is an intrinsic muscle that assists the flexor digitorum longus and flexing the toes but just from inside the foot itself.
- Tibialis posterior, which is an extrinsic foot muscle that helps support the arch and control pronation of the foot.
As the researchers expected, the MRI results from the runners displayed damage to several muscles after the marathon.
The extent and persistence of the foot muscle damage after running a marathon differed depending on the muscle group.
For example, one day after the marathon, there was evidence of muscle damage in the quadratus plantae muscle (7.5% increase in MRI intensity signal), flexor digitorum longus (4.7% increase in MRI intensity signal), tibialis posterior muscle (6.7% increase in MRI intensity signal) and flexor hallucis longus muscle (5.9% increase in MRI intensity signal).
There were no significant signal changes for muscle damage in two of the intrinsic foot muscles: the abductor hallucis and the flexor digitorum brevis.
The increased MRI signal intensity, again indicative of muscular damage and swelling, persisted until three days after the marathon in the tibialis posterior muscle (4.6% increase in MRI intensity signal 3 days post-marathon race).
Furthermore, there was a significant correlation between the muscular damage in the flexor digitorum longus and flexor hallucis longus from before the marathon to one day after the marathon relative to the changes in the arch height of the runners.
In other words, the damage in these muscles was associated with a decrease in arch height or a more significant flat-footed posture after the race.
What these results indicate is that certain foot muscles are more susceptible to damage with marathon running.
Furthermore, the extrinsic foot muscles are more susceptible to damage than the intrinsic foot muscles from marathon running and damage to the extrinsic foot muscles seems to be primarily responsible for the drop in arch height following marathon running.
As Dr. Fukano, the head researcher of the study said:
“These results indicate that the damage and recovery response after a full marathon differs among the various foot muscles. For our research participants, all three extrinsic muscles and only one intrinsic muscle showed damage after marathon running, suggesting that extrinsic muscles could be more susceptible to marathon-induced damage than the intrinsic ones.”
So, what does this mean in practical terms for marathon runners?
Ultimately, this is a relatively small study so the researchers did not draw sweeping implications based on the findings.
However, because it seems that the force borne on the ankle joint while running ultimately plays a big role in the potential muscular damage and changes in arch height following marathon running, it may be that we will begin to see suggestions from physiotherapists about how to properly strengthen the ankle and extrinsic foot muscles, and how to help support the recovery of these muscles after marathon running.
Dr. Fukano concluded:
“Since more people are now running for their fitness, our findings can provide runners and sports professionals insights on planning better recovery strategies focusing on muscle fatigue and damage to prevent running-related injuries and also improve runners’ conditioning.”
Staying abreast of the latest running research can sometimes be the ticket to staying healthy and enjoying the sport for life.
In the meantime, if you want to learn more about strengthening your feet for running, check out our guide toe spreaders for runners here.