Study suggests extrinsic foot muscles, which connect the lower leg and foot, are more susceptible to damage from marathon running — ScienceDaily

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The muscles of the foot are generally classified as intrinsic or extrinsic muscles. While intrinsic muscles originate from and insert within the foot, extrinsic muscles originate in the lower leg and insert into the foot through the ankle. Both muscle groups help stabilize the medial (inner) longitudinal arch of the foot. Although some studies have linked muscle swelling caused by long-distance running with decreased longitudinal arch, it has so far been challenging to associate this with intrinsic and extrinsic muscle damage.

Now, a new study explores the damaging effects of running a full marathon on the intrinsic and extrinsic muscles of the foot, and its association with changes in the longitudinal arch of the foot. The research team was led by Professor Mako Fukano from Shibaura Institute of Technology (SIT) and also included Kento Nakagawa from Waseda University, Ayako Higashihara and Takayuki Inami from Keio University, and Takaya Narita from Toin University. from Yokohama. Their findings were published online on April 27, 2023 at Scandinavian journal of medicine and science in sport.

The study recruited 22 university runners from athletic clubs who run at least 2 to 3 times per week and had registered for a full marathon race at the Mount Fuji International Marathon in either 2019 or 2021. The researchers first assessed magnetic resonance imaging (MRI) based on cross-sectional relaxation time (you₂), as an indicator of muscle damage, for participants’ intrinsic and extrinsic foot muscles at four intervals: before the marathon and 1, 3, and 8 days after running the full marathon. you₂ it is defined as the time it takes for the transverse magnetization vector in an MRI to decay to approximately 37% of its initial value, and is influenced by specific tissue characteristics.

The intrinsic muscles studied included the abductor hallucis (ABH), flexor digitorum brevis (FDB) and quadratus plantae (QP) and the extrinsic muscles included the flexor digitorum longus (FDL), tibialis posterior (TP) and flexor hallucis longus. (FHL). ). The researchers also determined longitudinal arch height using a three-dimensional analysis of foot stance for 10 of these participants at the same time intervals as the you₂ Magnetic resonance imaging to determine changes in the height of the longitudinal arch of the foot.

Compared to the values ​​of T₂ before the marathon, the researchers observed that the T₂ QP, FDL, TP, and FHL values ​​increased significantly one day after the marathon and varied throughout the observation period. In addition, they also found that the increase in T₂ of TP persisted three days after the marathon. However, they did not observe any important difference in T₂ for ABH and FDB. The team also found no significant changes in toe flexor muscle strength in any of the participants. Interestingly, they also noted that the arch height ratio decreased statistically from before the marathon to 1 and 3 days after the race, and this change could be related to T₂ changes in FDL and FHL.

“These results indicate that the damage and recovery response after a full marathon differ among the various foot muscles. For our research participants, all three extrinsic muscles and only one intrinsic muscle showed damage after marathon running, which which suggests that extrinsic muscles might be more susceptible to marathon-induced damage than intrinsic ones,” explains Prof. Fukano. This prominent damage to the extrinsic muscles of the foot reflects the greater stress placed on the ankle joint during long-distance running compared to the rest of the foot, something other studies have also shown. Since QP is linked to FDL and/or FHL, it may also have a secondary function in running, along with the extrinsic foot muscles, making it the only intrinsic foot muscle to be damaged in marathon running. Furthermore, the correlation between FDL and FHL and longitudinal arch height indicates that marathon-induced damage to these extrinsic muscles could be a factor in decreased arch height.

“As more people now run for fitness, our findings may provide runners and sports professionals with information on planning better recovery strategies focused on fatigue and muscle damage to prevent running-related injuries and also improve conditioning of the runners,” concludes Professor Fukano.