Plantar fasciitis is the third most common running-related overuse injury. It is speculated that weak intrinsic foot muscles (the muscles that begin and end within your foot) cause a lack of support to the medial longitudinal arch in the foot. This causes an increased strain on the plantar fascia, and causes us that dreaded heel pain!
Researchers at The Hong Kong Polytechnic University decided to compare intrinsic foot muscle (IFM) strength between experienced runners with and without chronic plantar fasciitis. The researchers examined total, rearfoot, and forefoot volume of the IFMs. They did so by examining muscle volume via magnetic resonance imaging (MRI).
So what did they learn? They found a significant difference in the rearfoot muscle volumes between the two groups! There was a trend towards statistical significance for total IFM volume, but the forefoot volume between the two groups was similar. This may suggest that rearfoot muscle strengthening should be the focus of rehabilitation protocols for patients with chronic plantar fasciitis.
This gives us some useful information, but the researchers did not analyze specific muscles in this study. The researchers also did not provide a causal relationship between IFM volume and the incidence of plantar fasciitis, as this was a cross-sectional study (basically, there may have been a correlation without causation situation here). Regardless, physical therapy interventions should certainly include IFM retraining to assist in the treatment of chronic plantar fasciitis!
Cheung, R., Sze, L., Mok, N., & Ng, G. (2016). Intrinsic foot muscle volume in experienced runners with and without chronic plantar fasciitis. Journal of Science and Medicine in Sport, 19(9), 713-715. doi: 10.1016/j.jsams.2015.11.004
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