Irene Davis, Ph.D.: Evolution of the Foot, Running Injuries, and Minimalist Shoes

Evolution of Running and Biomechanics

• Irene Davis’ background in physical therapy and biomechanics led her to study the relationship between mechanics and injuries
• Her interest in biomechanics was sparked by observing the movement of people with quadriplegia, who have to move their entire body with only 25% of their muscle power
• Davis’ research in foot orthotics and impacts in running led her to question the use of permanent bracing for feet
• She realized that feet have muscles that can be strengthened, just like other muscles in the body
• Studies showed that matching foot type to shoe type (motion control, cushioned, stability) did not result in differences in injury patterns
• This led Davis to reevaluate her approach to footwear and orthotics, and consider the evolutionary aspects of running and biomechanics
  Evolution of Human Feet and Running
• Human feet evolved for walking and running 
  • Transition from walking man (stereopithecus) to running man (Homo erectus)
  • Development of longitudinal arch, larger joint surfaces, and longer Achilles tendon
• Running for 2 million years 
  • Brains getting bigger, needed meat, outrun prey for endurance
  • Humans not fast runners, but good endurance runners
  • Panting off heat, outrunning large animals

Footwear in Human History

• First footwear found in Fort Rock, Oregon, dated 10,000 years old 
  • Made of sagebrush bark, flat surface with straps
  • Purpose: protect the bottom surface of the foot from the elements
• Human feet develop calluses for protection 
  • Going barefoot can lead to protective calluses on the bottom of the foot

Evolution of Running Shoes

• Origin of cushioned running shoes in Oregon
• Early Olympic athletes in marathons wore minimal footwear
• Modern running shoes designed for cushioning and support, but may not be necessary for all runners
  History of Running Shoes and Injuries
• Early running shoes were minimal, flat, and provided protection for the bottom of the foot 
• Running boom in the 1970s led to more people running, many of whom were not as fit as previous runners 
  • Resulted in an increase in running injuries, such as Achilles problems
  • Led to the addition of a heel lift in running shoes
• Two types of running shoes developed: motion control and cushioning shoes 
  • Motion control shoes: stiff heel counter, stiffer material on the inside of the midsole, plastic support reinforcements, and more arch support to prevent the foot from rolling in
  • Cushioning shoes: designed for people with high arches who need more cushioning
• Majority of running injuries occur from the knee down, with the knee being the primary attenuator of shock 
  • Ground reaction force when landing during running is about 2.5 to 3 times a person’s body weight
  • Force at the knee can be up to 7 times a person’s body weight
• Nike consulted sports podiatrists to address the rise in running injuries 
  • Determined that injuries were related to too much impact and too much motion
  • Led to the development of motion control and cushioning shoes
• Providing cushioning in shoes can actually cause people to land harder 
  • Studies have shown that removing arch support strengthens foot muscles
  • Cushioning may cause people to hit harder due to protection and mass effect
  • Lack of data on foot strike patterns before cushioned shoes, but it is believed that humans evolved to land on the balls of their feet
    Running Mechanics and Evolution
• Humans evolved to run on the balls of their feet 
  • Prehistoric vases depict humans running on the balls of their feet
  • Boston robot runs on the balls of its feet
  • Human lower leg designed to carry more load in the back than in the front
• Heel striking vs. forefoot striking 
  • Heel striking can be advantageous on soft surfaces, but on firm surfaces, there’s more tendency to land on the ball of the foot
  • Heel striking has a distinct impact peak, while forefoot striking has a gentle curve
  • Steeper slope of impact peak in heel striking is associated with a greater rate of loading, which is related to running-​​related injuries
• Running as an activity of daily living 
  • Running is ingrained in humans for fight or flight
  • Most people can run, but there may be exceptions due to leg length discrepancies or extreme foot deformities
• Importance of physical fitness in children 
  • La Sierra High School program in Carmichael, California, implemented a Marine-​​type boot camp program for all students to improve physical fitness
  • Program was highly motivational and encouraged teamwork and progression
    Physical Fitness and Running
• 30-​​year program with 800,000 kids per class 
  • Only 21 made it through the program
  • Resulted in extremely fit children and teenagers
• Program used simple exercises to build strength and physical literacy 
  • Monkey bars, push-​​ups, calisthenics, pegboards, man carries
• Participants now aged 55–79
  • Proposed study to follow up on their fitness and compare to a control group
• Documentary on the program shows participants attributing their success to the program 
  • Many came from troubled homes
• All participants were fit and strong, with different body types 
  • Belief that everyone with a normally intact neuromuscular system has the potential to be fit and strong

Running and Fitness

• Running is innate for those with a normally intact neuromuscular system 
  • Overweight teenagers should not start with running, but rather build strength and motor control first
• Obese individuals can run without pain if they run on the ball of their foot 
  • Softens the landing and reduces impact

Force Plate Treadmill

• Measures force in vertical, anterior-​​posterior, and medial-​​lateral directions
• Comparing minimalist vs. maximalist shoes and heel vs. toe strike 
  • Heel strike in cushioned shoes: higher slopes and load rates
  • Forefoot strike in regular shoes: greater force in anterior-​​posterior and medial-​​lateral directions
  • Forefoot strike in minimal shoes: reduced slopes and forces in all directions
• Recommendations:
  • Forefoot strike should be done in minimal shoes
  • Rearfoot strike should have cushioning under the heel

Minimalist Shoes

• No elevation of heel and no cushion or support 
  • Examples: Zero, Vivo Barefoot, Innovate
• Wider toe box allows for spreading of toes, enhancing foot function 
  • Similar to how hands function better when not restricted by tight gloves
    Minimal Shoes and Orthotics
• Minimal shoes: no cushioning, no arch support, flexible heel counter and upper 
• Vibram lawsuit: false advertising of increased muscle size with shoe use 
  • Led to shoe companies adding more to minimal shoes (e.g., New Balance Minimus)
• Partial minimal shoes: closer to regular shoes than barefoot 
  • Can lead to more injuries if still heel striking with less cushioning
• Transitioning from orthotics to minimal shoes 
  • Educate patients on the importance of strengthening foot muscles
  • Slowly wean patients off orthotics over 2–3 weeks
  • Introduce foot strengthening exercises
  • Once comfortable without orthotics, introduce minimal shoes for walking 
    • Walking in minimal shoes can be as effective as a foot strengthening program
  • Brands to try: Innovate, Vivo Barefoot, and Xero Shoes
    Transitioning to Minimal Shoes and Foot Strength
• First goal of therapy: go through daily activities without full arch support 
• Foot strengthening program (PreGate program) can take 1–3 months 
  • Addresses foot, hip, and knee issues
  • Teaches people how to engage foot muscles during activities
  • Includes off-​​treadmill activities like hopping, lunging, and jump roping
• Transitioning to minimal shoes requires time and gradual introduction 
  • Start with walking, then interject running slowly to avoid injuries like plantar fasciitis or metatarsal stress fractures
• Importance of foot muscle balance to protect bones and prevent stress fractures

Orthotics and the Podiatry Field

• Some podiatrists are starting to view orthotics as temporary solutions
• Younger podiatrists may be more open to treating patients with exercise rather than orthotics
• Goal: get people back into minimal shoes for better foot development and strength across the lifespan 
  • Important for children, adults, and aging populations
  • Minimal shoes provide more stability and preserve foot strength

Analogy: Feet as Tires on a Race Car

• Feet are the only points of contact with the ground, like tires on a race car
• Cramming feet into narrow shoes with less contact to the ground is like reducing tire grip and stability
• Importance of connecting to the ground for better overall performance and foot health
  Transitioning to Forefoot Strike and Minimalist Shoes
• Learning to forefoot strike: 
  • Some people may naturally transition when running barefoot
  • Short bursts of practice with rest to maintain technique
  • Can learn from books, courses, or personal experience
• Starting barefoot:
  • Provides sensory input for the feet
  • Can help teach proper running technique
• Running on different surfaces: 
  • Hard surfaces teach leg compliance
  • Soft surfaces may cause leg stiffness
  • Train on the surface you’ll be running on most often
• Knee vulgus and alignment issues: 
  • Not always a direct cause of injury
  • Injuries can be multifactorial (structure, movement, dosage)
  • Most common alignment issues: high impacts, medialization of the leg
  • Knee vulgus, inward rotation of the leg, and pelvic drop are common malalignments
    Evolution and Core Stability
• Sitting too much leads to weak core muscles 
• Core instability affects foot and lumbo pelvic core
• Strong core needed for proper running mechanics

Hip Hiking and Pelvic Stability

• Hip hiking occurs when one side of the pelvis drops
• Opposite side hip muscles responsible for keeping pelvis level
• Core muscles, including small stabilizing muscles and abdominals, play a role in preventing pelvic tilt and rotation

IT Band Syndrome

• IT band connects to tensor fascia lata muscle at the hip
• Exacerbated by inward angulation of the thigh and dropping of the pelvis
• Can be caused by excessive pronation (inward rolling) of the foot or issues with the hip
• Strengthening glute medius can help alleviate IT band pain

Physics and Biomechanics

• Biomechanics is a combination of physics and medicine
• Ground reaction forces and muscle forces play a role in joint compression and force amplification
• Understanding forces and moment arms can help identify and address biomechanical issues
  Adaptable Human Mechanics and Gait Retraining
• Human bodies are adaptable, especially in mechanics 
• Mechanics can be modified, unlike bone structure
• Gait retraining can help change movement patterns 
  • Requires practice, feedback, and patience
  • Can help prevent injuries and improve running mechanics

Gait Retraining for Injured and Non-​​Injured Individuals

• Most people who undergo gait retraining have existing injuries
• Preventative gait retraining could potentially reduce injury rates 
  • Study showed 62% reduction in injuries for novice runners who were trained to land softer
• Retrospective study on Harvard track team found forefoot strikers had half the injuries of rearfoot strikers

Minimal Shoes and Reduced Injuries

• Closed Christian community’s physician found relief from foot problems with minimal shoes
• Community members transitioned to minimal shoes, reducing referrals to podiatrists
• Cross country team in the community transitioned to minimal shoes, resulting in fewer injuries and improved performance
• Hypothesis: starting children with minimal shoes and proper running mechanics could reduce injuries and improve overall running health
  Facilitating Natural Movement in a Modern World
• Modern footwear increases torques on feet 
  • Unclear if this causes problems, but it’s beyond what we’re adapted for
• Encourage minimalist footwear and natural movement from birth 
  • Avoid sitting in chairs, promote squatting and standing
• Implement physical education in schools daily 
  • Calisthenics, push-​​ups, sit-​​ups, monkey bars, etc.
• Alarming statistics on chronic diseases in adolescents 
  • Diabetes rates increasing in children
• Encourage multi-​​sport athletes instead of single-​​sport specialization 
  • Reduces burnout and injury rates

Importance of Malleable Thinking

• Changing views based on new evidence is a sign of good thoughtfulness
• Continuously learning and adapting to improve human health and well-being