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Peter Attia MD#128 – Irene Davis, Ph.D.: Evolution of the foot, running injuries, and minimalist shoes
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CHAPTERS
- 0:11 – 7:23
Irene Davis's path from FBI hopeful to running biomechanics
Peter Attia introduces Irene Davis and her credentials, then asks how she came to her work. Davis describes moving from exercise science to physical therapy to a biomechanics Ph.D. with Peter Cavanagh, and the cousin whose quadriplegia sparked her interest in biomechanics.
- •Davis wanted to be an FBI agent until J. Edgar Hoover's reply said women weren't allowed
- •She earned her Ph.D. in biomechanics at Penn State under Dr. Peter Cavanagh, a pioneer in running mechanics
- •She combined a clinical physical therapy perspective with biomechanics to study mechanics and injury
- •A cousin's diving accident led to her start in spinal cord rehab and her interest in how people move with limited muscle power
- 7:23 – 10:37
How Davis's thinking on orthotics changed
Davis explains how she moved from prescribing orthotics for life to questioning them. Research on impacts, the Born to Run book, and a large military shoe-matching study pushed her to change her view.
- •She once taught and made foot orthotics and believed some feet couldn't support themselves
- •Rehab experience, where bracing is minimized, contradicted how she treated feet
- •A military study of about 7,000 people found no difference in injuries when shoes were matched to foot type
- •Peter Attia praises her willingness to change her mind in light of new evidence
- 10:37 – 17:54
Evolution of the foot and the move from walking to running
Davis describes anatomical changes in the transition from walking to running, drawing on the Bramble and Lieberman paper. She covers the complexity of the foot and why humans are endurance rather than speed runners.
- •The arch, larger joint surfaces and a longer Achilles tendon developed to handle running forces
- •The foot has 26 bones, 33 articulations and four layers of arch muscles
- •Humans have been running for about 2 million years
- •Humans pant off heat, which let them run prey to exhaustion
- 17:54 – 26:02
Early footwear and the rise of the cushioned running shoe
The conversation covers early footwear, why humans needed protection for their feet, and how running shoes developed after the running boom. Davis explains how Achilles problems led to heel lifts and how podiatrists' advice produced motion control and cushioned shoes.
- •Ancient shoes found in Oregon were simple protective sandals
- •Until about the 1960s, athletic footwear was essentially minimal
- •Achilles injuries led to added heel lift, the origin of heel-to-toe drop
- •Nike brought in sports podiatrists, who attributed injuries to too much impact and motion, producing motion control and cushioned shoes
- 26:02 – 34:11
Running injuries, impact forces and why cushioning backfires
The discussion turns to where running injuries occur and the size of the forces on the knee. Davis argues that cushioning leads people to land harder and that support weakens foot muscles, and discusses heel versus forefoot striking.
- •Most running injuries occur from the knee down, and the knee is the most common site
- •Peak ground reaction force is about 2.5-3 times body weight, and up to about seven times at the knee
- •Cushioning lets people land harder, and arch support weakens foot muscles
- •Heel pad pain thresholds and other studies suggest footwear shifted us from forefoot to rearfoot striking
- 34:11 – 40:20
Shin splints, load shifting and rate of loading
Davis and Attia explain shin splints and how foot strike shifts load between the calf and the knee. They explain the impact peak and rate of loading and its link to injury.
- •Shin splints come from overusing the small muscle in the front of the leg when landing on the heel
- •Forefoot striking shifts load to the calf, while heel striking shifts it to the knee
- •Heel strikers show an impact peak followed by a propulsive peak, while forefoot strikers show a smooth curve
- •Steeper loading rate is related to running injuries
- 40:20 – 47:07
Can everyone run? Fitness, physical literacy and the La Sierra program
Attia asks whether some people shouldn't run. Davis says running is innate, describes the La Sierra High School fitness program, and explains why unfit people should build strength first and why the million foot strikes a year matter.
- •Davis says running is an innate activity of daily living, not a skill, with exceptions for extreme structural problems
- •The La Sierra program built fitness and physical literacy in every student without fancy equipment
- •Unfit people should build strength and motor control before running
- •Going from rearfoot to forefoot strike removes the impact peak but not the peak force
- 47:07 – 52:02
Force plate effects of shoes and strike pattern
Attia asks what a force plate shows across shoe and strike combinations. Davis explains differences in vertical, anterior-posterior and mediolateral forces and recommends minimal shoes for those switching to a forefoot strike.
- •Cushioned shoes tend to produce heel striking and higher load rates
- •Forefoot striking in regular shoes brings more plantar flexion, braking force and inversion
- •Forefoot striking in minimal shoes gives the softest landing in all three directions
- •Transitioning to a forefoot strike should be done in minimal shoes, and rearfoot strikers should have cushioning
- 52:02 – 1:00:05
What counts as a minimalist shoe, and the Vibram and Nike Free story
Attia and Davis define minimalist shoes and name brands. Davis explains why partial minimal shoes can be a problem, referring to the Vibram lawsuit and the history of the Nike Free.
- •Davis defines a minimal shoe as one you can roll up, with no cushioning or arch support, a flexible heel counter and upper
- •The Vibram lawsuit was about false advertising on muscle size, not injury
- •Partial minimal shoes lead people to run more like they do in regular shoes
- •One 12-week study found partial minimal shoes had twice the injuries of minimal shoes
- 1:00:05 – 1:07:04
Weaning off orthotics and building foot strength
Davis describes how she educates patients and gradually weans them from orthotics while strengthening their feet. She cites a study showing walking in minimal shoes strengthened feet almost as much as a foot-strengthening program, and describes her pre-gait program.
- •Davis uses a neck brace analogy to explain why long-term orthotics weaken the foot
- •Weaning takes about two to three weeks, with orthotics removed for short periods
- •Walking in minimal shoes strengthened feet nearly as much as the Foot Core program in a study
- •The pre-gait program of one to three months builds foot, hip and knee strength before treadmill retraining
- 1:07:04 – 1:15:58
Foot muscle size and the podiatry field's response
The conversation covers evidence that minimal shoes enlarge foot muscles and orthotics shrink them. Davis discusses the lack of strengthening in plantar fasciitis guidelines and how the podiatry field is slowly changing, and extends minimal shoes to children and aging.
- •Minimal shoe running increased foot muscle volume and cross-sectional area
- •A study found 12 weeks in orthotics reduced intrinsic muscle size by 10-17%
- •Plantar fasciitis guidelines recommend everything but strengthening
- •More podiatrists are treating orthotics as temporary
- •Minimal shoes may benefit children, adults and aging people
- 1:15:58 – 1:22:01
Learning to forefoot strike and why to train on hard surfaces
Attia raises the race-car tire analogy and asks how people can learn to forefoot strike. Davis shares her own experience starting barefoot and explains why leg stiffness on soft surfaces means training should include hard ones.
- •Attia compares feet to the tires on a race car, which are the only contact with the road
- •Davis says people tend to overthink running technique and that barefoot running lets the feet teach you
- •The leg stiffens on soft surfaces and becomes compliant on hard ones
- •Davis advises doing a good part of training on the surface where most running will happen
- 1:22:01 – 1:28:34
Knee valgus, pelvic drop and core stability
Attia asks about knee valgus and Davis explains that injuries are multifactorial. She describes the common pattern of high impacts and medialization of the leg, linking it to weak core and hip stability and to hardware versus software.
- •Injuries depend on structure, motor control and dosage, not on alignment alone
- •Over 700 clinic patients showed high impact and leg medialization as the most common features
- •Pelvic drop on the opposite side results from weak stabilizers on the stance side
- •Davis frames strength as hardware and motor pattern as software
- 1:28:34 – 1:36:10
IT band syndrome and the physics of joint forces
Davis explains her prospective and retrospective studies on IT band syndrome, linking it to thigh angulation, pelvic drop and tibial rotation from the foot. The talk moves to Newtonian physics and how joint forces are amplified.
- •Both studies found greater inward thigh angulation in runners with IT band syndrome
- •Pelvic drop and internal tibial rotation also stretch the IT band
- •Excessive pronation can internally rotate the tibia
- •Ground reaction force follows Newton's third law, and muscle forces compress joints and amplify load
- 1:36:10 – 1:46:36
Gait retraining, prevention studies and a minimal shoe case study
Davis explains that gait can be retrained through feedback and practice, describes her clinic's program, and notes that insurance requires an injury. She cites a study with a 62% injury reduction, Harvard track data and a Christian community's cross-country team that transitioned to minimal shoes.
- •Gait retraining requires feedback, fading it, and lots of practice over weeks
- •The program runs about two months of pre-gait, four weeks of treadmill retraining, then 10 supervised weeks
- •A study of 320 novice runners trained to land softer saw a 62% reduction in injuries over a year
- •A cross-country team transitioning to minimal shoes over nine months had almost no injuries and won its division
- 1:46:36 – 1:53:05
Modern environment, children's health and closing
Davis and Attia discuss how shoes add torque and how chairs and minimal footwear in childhood would help health. Davis calls for daily physical education and multi-sport play, and the conversation ends with thanks.
- •Joint torques at ankle, knee and hip are lowest barefoot and rise with footwear
- •Attia would put minimalist footwear and avoiding chairs among his top five changes for health
- •Davis wants daily physical education with calisthenics and climbing
- •Single-sport kids burn out sooner and get injured more, per Davis
