What Shapes Your Foot Posture?Plantar Fascia, Foot Muscles and Flat Feet

What the study looked at

Why does one person have a flat foot and another a normal arch? The plantar fascia and the many small and large muscles of the foot all pull across its joints, but until this study, no one had measured how much each individual structure actually contributes to foot posture.

The researchers recruited 111 adults and used the Foot Posture Index to classify them as having a normal foot (68 people) or a flat, pronated foot — pes planus (43 people). Ultrasound was then used to measure the thickness of the plantar fascia at three regions along the arch, and the cross-sectional area (a proxy for size and strength) of six foot muscles, both the intrinsic muscles inside the foot and the extrinsic muscles running down from the lower leg. Statistical modelling then worked out which structures best explained the differences in foot posture.

What the study measured

What the results showed

Five structures together explained about 69% of the variation in foot posture — and one of them stood out well above the rest.

What this means for practice

Foot posture sits underneath a huge range of lower-limb complaints — heel pain, shin pain, knee and hip issues in runners, and more. This study helps practitioners understand which foot structures are doing the most work in shaping the arch, which is useful when assessing a flat-footed client and deciding where to focus.

It also puts numbers to something clinicians see often: the plantar fascia is central to arch support, and the muscles on the inner side of the foot matter more than the outer ones.

Clinical relevance by discipline

Limitations to be aware of

This was a cross-sectional study, so it can only show associations — it cannot prove that changing the plantar fascia or a muscle would change someone's foot posture. It measured static standing posture rather than the foot in motion, and muscle cross-sectional area is only a proxy for how a muscle actually performs. Only normal and flat feet were included, so high-arched (cavus) feet — the other end of the spectrum — weren't represented. The authors also note an unequal gender balance, unadjusted age and BMI differences, and that ultrasound measurement is user-dependent.

These points mean the findings are best read as a well-measured map of what's associated with foot posture, and a strong starting point for future work, rather than a treatment recommendation on their own.

Summary

In 111 adults, the plantar fascia and the medial foot structures were the main contributors to static foot posture. The forefoot region of the plantar fascia alone explained 52% of the variation, and five structures together explained 69%. Both intrinsic and extrinsic foot muscles played a part, but each contributed far less than the fascia.

For myotherapists, physiotherapists and remedial massage therapists, this reinforces the central role of the plantar fascia and the value of assessing the medial foot and intrinsic muscles in flat-foot presentations — while keeping in mind that this is an associative study, not proof that targeting these structures will change the arch.