Ready, set, go: New study shows how marathon running affects different foot muscles

With the growing emphasis on fitness and health, a lot of individuals have incorporated long-distance running into their exercise routines. They also participate in different marathons at local, national, and international levels. However, marathon running can cause exhaustion and harm to the muscles in the feet, which may result in ongoing pain or injuries. Currently, there is limited knowledge available about how marathon running specifically affects the different muscles in the feet.

Foot muscles can be broadly classified into two categories: intrinsic and extrinsic muscles. Intrinsic muscles are those that originate and insert within the foot itself, while extrinsic muscles originate in the lower leg and connect to the foot via the ankle. Both groups of muscles play a role in stabilizing the inner (medial) longitudinal arch of the foot. Some studies have suggested that prolonged running can lead to muscle swelling, which may contribute to a reduction in the height of the longitudinal arch. However, it has been difficult to establish a clear link between this muscle swelling and damage to the intrinsic and extrinsic foot muscles.

A recent study conducted by a team of researchers, led by Professor Mako Fukano from Shibaura Institute of Technology (SIT), has delved into the harmful effects of participating in a full marathon on both intrinsic and extrinsic foot muscles. The team also included Kento Nakagawa from Waseda University, Ayako Higashihara and Takayuki Inami from Keio University, and Takaya Narita from Toin University of Yokohama. The results of their research were published online on 27th April 2023 in the Scandinavian Journal of Medicine & Science in Sports.

For the study, 22 college runners who were part of track and field clubs and ran at least 2-3 times a week were recruited. These runners had registered for the Mt. Fuji International Marathon in either 2019 or 2021. The researchers utilized magnetic resonance imaging (MRI) to measure the transverse relaxation time (T2) of the intrinsic and extrinsic foot muscles. T2 is a measure of muscle damage, with a higher value indicating greater damage. The participants’ foot muscles were assessed at four different time points: before the marathon, as well as 1, 3, and 8 days after completing the full marathon. This measurement helps to understand changes in the muscles over time, as T2 is influenced by tissue-specific characteristics.

The researchers focused on studying specific intrinsic and extrinsic foot muscles. The intrinsic muscles examined were the abductor hallucis (ABH), flexor digitorum brevis (FDB), and quadratus plantae (QP). The extrinsic muscles analyzed were the flexor digitorum longus (FDL), tibialis posterior (TP), and flexor hallucis longus (FHL). Additionally, the research team measured the height of the longitudinal foot arch using three-dimensional analysis of foot posture. This analysis was conducted on 10 of the participants, and the measurements were taken at the same intervals as the T2 MRI scans to determine any changes in the height of the longitudinal foot arch.

Upon comparing the T2 values before the marathon, the researchers noticed significant increases in T2 values for the quadratus plantae (QP), flexor digitorum longus (FDL), tibialis posterior (TP), and flexor hallucis longus (FHL) muscles one day after the marathon. These values continued to fluctuate during the observation period. Additionally, the T2 value for TP remained elevated even three days after the marathon. However, there were no significant differences in T2 values for the abductor hallucis (ABH) and flexor digitorum brevis (FDB) muscles. The researchers also did not observe any significant changes in toe flexor muscle strength among the participants. Interestingly, they discovered that the ratio of arch height showed a statistical decrease from pre-marathon to 1 and 3 days after the race. This change in arch height was found to correlate with the T2 changes observed in the FDL and FHL muscles.

These findings show that different foot muscles are affected differently during the process of damage and recovery after running a full marathon. In the study, all three outer muscles of the foot and only one inner muscle showed damage after running the marathon, suggesting that the outer muscles are more prone to damage compared to the inner ones. Professor Fukano explains that the extensive pressure on the ankle joint during long-distance running contributes to the significant damage observed in the outer foot muscles, which is consistent with findings from other studies. The inner muscle, known as QP, which is connected to FDL and/or FHL, may have a secondary role in running along with the outer foot muscles, and this is why it is the only inner foot muscle to be damaged during marathon running. Additionally, there appears to be a relationship between the height of the longitudinal foot arch and the damage to the FDL and FHL muscles, suggesting that marathon-induced damage to these outer muscles could contribute to a decrease in foot arch height.

Prof. Fukano concludes that since more people are engaging in running for their fitness, the study’s findings can be valuable for runners and sports professionals. These findings can help them plan more effective strategies for recovery, specifically targeting muscle fatigue and damage. By implementing these strategies, they aim to prevent running-related injuries and enhance the overall physical conditioning of runners.

Here’s hoping that these results can help get fitness enthusiasts off to a running start!