The Influence of Arch Type on Injury in Minimally-Shod Runners

We have known for some time that there are different running injury risk profiles for different foot types, often depending on how you choose to classify them. Now this new study is suggesting that different foot types may have different injury risk profiles between traditional shod running and minimalist shod running:

The Influence of Arch Type on Injury in Minimally-Shod Runners
Galbreath, K.M.; Harrison, K.D.; and McCrory, J.L.
International Journal of Exercise Science: Conference Proceedings: Vol. 9: Iss. 2, Article 25. 2014
Greater than 30% of runners are injured annually. In shod runners, individuals with high arches (pes cavus) are more likely to sustain a bony injury and those with low arches (pes planus) are more likely to sustain a soft tissue injury. However, this relationship has not been established in minimally-shod runners.
Purpose: To determine if arch type (pes cavus, pes planus) is related to location and type (bony, soft tissue) in minimally shod runners.

Methods: Sixteen experienced minimalist runners participated (age: 27.4±10.1 yrs, hgt: 170.3±25.0 cm, mass: 78.1±18.0 kg, gender: 8M, 8F). Informed consent was obtained. Arch index (AI) was obtained via an inked footprint. Subjects were surveyed about the type and location of pain felt while running. Pain in areas of common running injuries (hip, knee, ankle, lower leg, and foot) was quantified using a validated visual analog scale (VAS). Based on survey data, injuries were classified as soft-tissue or bony. Subjects were considered to be injured if pain on the VAS >3. Left and right side data were pooled together. Feet were classified as being pes cavus (AI < 0.21, n=7 feet), or pes planus (AI>0.26, n = 11 feet). Feet with normal arches (n = 14) were excluded from further analysis. Chi-squared analyses were performed to determine if arch type was related the incidence of soft-tissue or bony pain. Separate chi-squared analyses assessed if arch type was a factor in the location of pain. (α = 0.05).

Results. Runners with a pes cavus foot were more likely to report soft-tissue pain than those with a pes planus foot (PC: 85.7%, PP: 40.0%; p=0.040). No differences were found in the likelihood of runners with different arch types to report pain in the hip, knee, ankle, foot, or calf (p > 0.05).

Conclusions: The results of this pilot study seem to contradict the results of a study on shod runners. We found minimalist runners with a pes cavus foot more likely to report soft-tissue pain whereas others reported shod runners with a pes cavus foot more likely to sustain a bony injury. Soft tissue pain was reported by our subjects in the Achilles tendon, calf muscle, patellar tendon, peroneal tendon, plantar fascia, and a Morton’s neuroma. The loading mechanics of minimally-shod running need to be further investigated to determine why these runners with pes cavus feet are more likely to experience a soft-tissue injury.

I have never been much of a fan of static arch type measures as they don’t really reflect dynamic function, let alone reflect the different loads in the different tissues. It is the loads in the tissues that are important. These days we know way more about foot biomechanics than just to classify feet based on the dated ‘pes cavus’ and ‘pes planus’ categories.

Having said that this study does throw up an interesting observation, but first: I have no more information on this study than what is in the abstract (its from a conference). The sample size is down on the low side, but the authors do state that it was a pilot study – however the results were still statistically significantly different, so we have to go with that. I am a little uncomfortable about the combining of the left and right side data (issues to do with the assumption of independence for statistical testing), so would really like to see more data. There is also an issue (due to the small sample size), that some of the specific injuries may only have occurred once in the cohort and may have been due to some odd event and nothing to do with foot type. I am also uncomfortable about the use of survey data reported by the runners on their injury history and the actual accuracy of the diagnosis based on that. It is a bit difficult to pass judgement on these issues at this stage and hopefully they will be addressed when this study is published in full.

What caught my eye was three things:

1. The apparent different results between the minimalist runners in the above study and the traditional shod runners in another study (which they did not cite and I not sure which study they talking about!). I not sure of the validity of this type of comparison with seeing the full information on the above study and the full study that they were comparing it to; but if the observation stacks up, then this is something that is worth pursuing.

2. The observation that in the pes cavus group, they were more likely to report “Achilles tendon, calf muscle, patellar tendon, peroneal tendon, plantar fascia, and a Morton’s neuroma“. The implication being that the pes planus foot may be protective against these? It also not clear what was actually meant by the “bony injury” and the accuracy of the diagnosis of “bony injury” (eg was medial tibial stress syndrome considered a “bony” injury by the self reported nature of the data collection).

3. While the study was only a pilot with small numbers, it was interesting that 85% of the pes cavus group had a history of injury (it looks like it was 40% in the pes planus group), so minimalist runners do get injuries! (…and some do have flat pronated feet!).

As always, I go where the evidence takes me until convinced otherwise, and while interesting I not going to get too excited at this stage about this one.

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