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

KEYPOINTS

• 01

  Irene Davis moved from prescribing orthotics to minimising support

  Davis, a physical therapist and biomechanist who moved from the University of Delaware to Harvard, used to match shoes and orthotics to foot type. Her early instinct came from rehab, where the goal was to remove bracing so patients could build their own strength. Her cousin, who had quadriplegia, had to move 100% of his body with about 25% of his muscle power. Her views on running shoes shifted after she met the evolutionary biologist Dan Lieberman and joined his 2010 Nature paper.

• 02

  Matching shoes to foot type doesn't prevent injuries

  In Joseph Knapik's military studies of roughly 7,000 service members, people given shoes 'matched' to their arch type had the same injury rates as those who all got the same shoe. The arch types were motion-control shoes for flat, flexible feet, cushioned shoes for high, rigid arches and stability shoes for normal arches. Davis says that result made her question her own prescribing.

• 03

  Humans evolved as endurance runners

  With 26 bones and many small muscles, the foot is well equipped to walk and run without support. Lieberman's argument is that over 24 hours no animal can cover more distance than a human, because we shed heat through sweat while big animals such as kudu overheat. For about two million years we ran barefoot or in minimal footwear, like 10,000-year-old sagebrush sandals found at Fort Rock, Oregon.

• 04

  Running injuries became a research topic only after cushioned shoes arrived

  Olympic marathoners around 1900 ran in thin leather soles, and that remained broadly the case until the 1960s and 70s. Davis says the first running-injury articles appeared in the early 1970s, after cushioned, raised-heel shoes let people land on their heels without learning to cushion the landing. She concedes there's little good high-speed data from before cushioned shoes.

• 05

  The steepness of the impact matters, not just its peak

  Heel striking creates a sharp impact spike before propulsion. The steeper its slope, the higher the rate of loading, which studies link to running injuries. Forces at the knee can reach about seven times body weight, or 1,400 lb for a 200-lb runner. Several studies show people hit harder in highly cushioned shoes such as Hoka. Her rule: if you stay a rearfoot striker, keep cushioning under your heel.

• 06

  Retraining runners to land softly cut injuries by 62%

  In a study of 320 novice runners, half did eight treadmill sessions, building from 10 to 30 minutes, with visual feedback on their impact and the single instruction to land more softly. Over the following year, their injuries fell 62% compared with controls. They weren't told how to change their form.

• 07

  Orthotics weaken the foot, and minimal shoes strengthen it

  A study under review fitted healthy feet with orthotics for 12 weeks: intrinsic foot muscle size fell 10–17%, with no change in controls. In Sarah Ridge's study at BYU, gradually walking in minimal shoes strengthened the foot almost as much as an eight-week 'foot core' exercise programme. The arch has about 10 muscles in four layers.

• 08

  Make the transition slowly

  Davis's 'pre-gait' programme lasts one to three months, longer for older people, who are 'less plastic'. It includes foot strengthening, hip and knee work, teaching people to engage their foot muscles while moving, and hopping, lunging, plyometrics and skipping rope. Patients should be able to walk briskly for about 30 minutes in minimal shoes before adding running, or they'll load the foot faster than it can adapt.

• 09

  Knee valgus is the most common malalignment

  In more than 700 patients at her running injury clinic, the two most common features are hard landings and the leg collapsing inwards: knees coming in, the kneecap rotating inwards and the pelvis dropping on the opposite side. Her prospective and retrospective studies of IT band syndrome found the same pattern, which pulls on the band's attachment near the knee. Weak hip muscles let the pelvis drop.

• 10

  Shin splints are often a heel-striking overuse problem

  New runners who land on their heels must use the muscle at the front of the shin to lower the foot. Without conditioning, it becomes sore from overuse.