#128 – Irene Davis, Ph.D.: Evolution of the foot, running injuries, and minimalist shoes

Davis's Spaulding National Running Center has put over 700 injured runners through this pipeline. The pre-gait phase is not just foot work — it addresses the whole kinetic chain including hip abductor strengthening (gluteus medius), hopping, lunging, plyometrics, and jump rope. These are 'components of running' that load the system dynamically without the full treadmill dose. Once minimum strength and movement criteria are met, the treadmill phase begins. Feedback is faded gradually: the runner first learns with the trace visible, then works without it. The outdoor phase re-exposes the runner to variable terrain and pacing, where the brain must apply the new motor program without external cues.

Davis uses the neck-brace analogy with every patient: 'If you put someone in a neck brace for life, what's going to happen to your neck muscles?' The foot has ten arch muscles in four layers that respond to load like any other muscle group. The arch does not fall when orthotics are removed — provided the transition is done slowly with concurrent strengthening. Davis instructs patients to keep the orthotics physically with them throughout the weaning period — they are never taken away, only progressively unused.

Brands Davis has in her clinic for patient trials: Inov-8, Vivo Barefoot, and Xero. Xero is distinguished by its wide toe box, enabling toe splay — feet crammed into a narrow toe box are like hands shoved in tight gloves. Children should ideally be in minimal shoes from the start to allow normal developmental foot muscle strengthening.

Davis's clinic uses the term foot core deliberately — parallel to lumbar-pelvic core stability. Just as lumbar instability allows the primary movers to malfunction, foot-core weakness allows the ankle, knee, and hip to compensate poorly. The published study (Ridge et al., BYU) established equivalence between the structured foot-core program and minimal shoe walking at 8 weeks, with the exercise group showing slightly more volume gain. For motivated patients, the exercises on top of the walking transition are additive and maximize the strengthening effect.

Davis's lab published both retrospective and prospective studies on IT band mechanics that found the same results — people with ITBS showed greater inward thigh angulation and contralateral pelvic drop both before and after injury. She notes that the knee is the joint in the middle of the foot and the hip — it often is the victim of issues with the foot or the hip. Attia corroborates from personal experience: his IT band syndrome on the bicycle resolved completely after a robust eccentric glute medius strengthening program.

The recommendation to start on hard rather than soft surfaces follows from leg-spring stiffness modulation research: the body automatically stiffens on soft surfaces and becomes compliant on firm ones. Davis recounts Chris McDougall's advice to her: start barefoot and your feet will teach you. The pain feedback of landing on firm surface barefoot is the most honest coaching signal — it immediately tells the runner to move off the heel. Davis ran on hard pavement barefoot to retrain her own gait after years off from injury.

Davis explains that research shows this consistently: when people are given cushioning, they stiffen their landing less and hit harder. The body has an innate stiffness-regulation system — on hard surfaces, the leg becomes compliant; on soft surfaces, it stiffens. Cushioned shoes fool the brain into treating firm ground as soft, reducing the protective compliance response. The result is that the runner lands with greater instantaneous force transfer despite the foam. This is why Davis's clinical recommendation is binary: if you are committed to heel striking, you must maintain adequate cushion under the heel and replace the shoe every 300–500 miles. If you want to forefoot strike, transition to a minimal shoe so the brain gets honest feedback.

On a force plate, a rearfoot striker shows two distinct peaks: a sharp, tall impact peak followed by a propulsive peak. A forefoot striker shows a single smooth curve with no separate impact transient. The load rate — the slope of that initial rise — is what Davis's lab measures as the injury predictor. When forefoot striking is combined with minimal shoes, the load rate drops in all three directions: vertical, anterior-posterior (braking force), and medial-lateral. In conventional shoes, forefoot strikers often land in excessive plantarflexion and inversion, creating high achilles and peroneal tendon loads — which is why many people who try to forefoot strike in cushioned shoes develop new injuries.

Davis makes the analogy explicit: 'If you put someone in a neck brace for life, what's going to happen to your neck muscles? And they say, well, they're going to get weak.' The foot arch has ten muscles in four layers — the same tissues that get stronger in minimal shoe interventions. Her clinic's weaning protocol treats orthotics as a temporary scaffold, not a permanent replacement. The study presented at the meeting was 12 weeks of orthotics in healthy adults — a relatively short exposure to produce a 10–17% volume reduction, implying that years of wear could produce considerably greater atrophy.

The practical implication is that the transition to minimal shoes can itself serve as the rehabilitation intervention, not just the endpoint. Davis's clinic uses this finding to get patients started on walking in minimal shoes during the orthotics weaning phase — they are simultaneously weaning support and building strength. The foot-core group had slightly more strengthening than the walking group, suggesting a combined approach is additive, but the walking-alone effect was large enough to be clinically meaningful. This also supports Davis's public health argument: if the default footwear for all walking was minimal, foot muscle atrophy from footwear would be largely prevented without any additional exercise.

The eight sessions ranged from 10 to 30 minutes in a progressive ramp. The feedback was the force-plate trace — runners could see their impact peak in real time and self-organize to reduce it. Davis notes the study's limitation: subjects were not brought back to confirm that the gait change persisted, so it is unknown whether the improvement was maintained or whether some runners reverted and were protected by a different mechanism during the follow-up period. A retrospective study from Dan Lieberman's group on the Harvard track team found forefoot strikers had half the overuse injuries of rearfoot strikers — converging evidence from both experimental and observational designs.