#128 – Irene Davis, Ph.D.: The evolution of the foot, running injuries, and minimalist shoes
Dr. Irene Davis, founding director of the Spaulding National Running Center, discusses how modern footwear has altered human biomechanics, leading to running injuries. She advocates for minimalist shoes and gait retraining to restore natural foot strength and movement patterns.
Deep Dive Analysis
20 Topic Outline
Irene Davis's Path to Biomechanics and Physical Therapy
Evolution of Thinking: From Orthotics to Intrinsic Foot Strength
Human Foot Evolution: From Walking to Endurance Running
Impact of Modern Footwear on Running Injuries
Running Injuries: Distribution and Common Sites
Cushioned Shoes, Heel Striking, and Impact Forces
Understanding Shin Splints and Lower Leg Muscles
Biomechanics of Foot Strike: Load Shift and Impact Peaks
Minimalist vs. Conventional Shoes and Foot Strike Interaction
The Vibram Lawsuit and Its Effect on Minimalist Footwear
Protocol for Transitioning Off Orthotics
Foot Muscle Volume, Minimalist Shoes, and Orthotics Research
Importance of Minimalist Shoes Across the Lifespan
Running Surface and Leg Stiffness Modulation
Knee Valgus and Malalignment in Running Injuries
Causes and Biomechanics of IT Band Syndrome
Physics of Ground Reaction Forces and Joint Amplification
Challenges and Effectiveness of Gait Retraining
Preventative Gait Retraining and Injury Reduction
The Importance of Physical Literacy and Varied Movement
7 Key Concepts
Motion Control Running Shoe
A type of running shoe designed with a stiff heel counter and stiffer material on the inside of the midsole. Its purpose is to prevent excessive inward rolling of the foot, often including plastic support reinforcements and increased arch support.
Cushioning Running Shoe
A type of running shoe typically designed for individuals with high, rigid arches that do not move much. These shoes provide additional padding to absorb impact forces.
Heel-to-Toe Drop
The difference in height between the heel and the toe of a shoe. This feature was introduced in athletic footwear to compensate for Achilles tendon issues that arose when runners transitioned from heeled walking shoes to flat running shoes.
Load Rate
Refers to the quickness with which force is applied to the body, specifically the steepness of the first impact peak in ground reaction force. A higher load rate, characterized by a rapid rise to peak force, is associated with running-related injuries.
Minimalist Shoe
A shoe characterized by its flexibility, lack of cushioning, absence of arch support, and a flexible heel counter and upper. It's often described as being able to be rolled up and put in a pocket, allowing the foot to function more naturally.
Foot Core
Analogous to the lumbopelvic core, referring to the intrinsic muscles of the foot. These muscles are crucial for providing stability and enabling the foot's diverse functions, such as acting as a stable base, adapting to uneven terrain, attenuating shock, and serving as a spring or rigid lever.
Leg Spring Stiffness Modulation
The innate ability of the human leg to adjust its stiffness dynamically based on the landing surface. On soft surfaces like sand, the leg stiffens to prevent collapse, while on hard surfaces like concrete, it becomes more compliant to attenuate shock.
14 Questions Answered
Her thinking evolved due to research showing lower impacts with forefoot striking (common in barefoot runners), the realization that physical therapy aims to reduce support, and studies indicating no difference in injury patterns when matching shoes to foot type.
As humans transitioned from walking to running (Australopithecus to Homo erectus), the medial longitudinal arch developed, joint surfaces enlarged to distribute higher forces, and the Achilles tendon lengthened to store energy, optimizing the foot for endurance running.
The running boom in the 1970s, coupled with new shoe designs, led to a rapid increase in running injuries, particularly Achilles problems, as shoes added heel lifts and cushioning, altering natural biomechanics.
Cushioned shoes can paradoxically cause people to land harder, as the perceived protection encourages a more forceful impact. This can lead to a quicker application of force to the body, known as a higher load rate.
A shin splint is pain on the front part of the lower leg, typically in the tibialis anterior muscle. It occurs in new runners who heel strike because this pattern requires the smaller front leg muscles to eccentrically control the foot's descent, leading to overuse injury.
Landing on the ball of the foot shifts the load from the quadriceps and knee to the ankle and calf, whereas heel striking shifts the load from the calf to the knee, which is the most common site for running injuries.
A minimalist shoe is characterized by its ability to be rolled up, having no cushioning, no arch support, a flexible heel counter, and a flexible upper, allowing the foot to move and strengthen naturally.
Orthotics provide extrinsic support, which can lead to a reduction in the size and strength of the foot's intrinsic muscles. Studies have shown a 10-17% reduction in intrinsic muscle size after 12 weeks of orthotic use in healthy feet.
While there are exceptions for extreme deformities or neurological disabilities, most people with a normally intact neuromuscular system can run, as it is an innate activity. However, individuals who are not fit should gradually build strength and motor control before starting to run.
Transitioning too quickly can overload the foot and ankle, potentially leading to injuries like plantar fasciitis or metatarsal stress fractures. The foot needs time to adapt and strengthen to the increased demands of less support and a different strike pattern.
Knee valgus is an inward angulation of the knees, where they bow towards each other. It is a common malalignment pattern associated with running injuries, often accompanied by inward rotation of the leg and pelvic drop, indicating core and hip instability.
IT band syndrome is often caused by excessive inward angulation of the thigh and/or pelvic drop, which stretches the IT band. It can also be exacerbated by internal rotation of the tibia, which can be influenced by excessive pronation (inward rolling) of the foot.
Training on hard surfaces teaches the leg to be compliant, meaning it learns to flex ankles, knees, and hips to attenuate shock. This is crucial for runners who primarily compete or run on hard surfaces, as it trains the muscles to absorb impact effectively.
Yes, a study with novice runners showed a 62% reduction in injuries over a year in a group trained to land softer (often by reducing impact spikes) compared to a control group, suggesting that modifying gait mechanics can be a powerful preventative measure.
18 Actionable Insights
1. Strengthen Foot Muscles Intrinsically
Recognize that your feet contain 10 muscles in four layers, capable of strengthening just like your quads or biceps. Challenge the mindset that feet inherently require permanent external bracing, as continuous support can weaken these muscles.
2. Gradually Wean Off Orthotics
If using orthotics, slowly reduce their use over two to three weeks, starting with short periods (e.g., an hour) without them. Simultaneously, perform foot strengthening exercises and listen to your body, reinserting orthotics if feet become sore, to allow intrinsic muscles to adapt and strengthen.
3. Adopt Minimalist Footwear
Transition to minimalist shoes (no midsole, no arch support, flexible heel/upper, rollable) for walking and eventually running. This choice strengthens foot muscles and allows feet to function as they evolved, potentially reducing injury risk across the lifespan.
4. Transition to Forefoot Strike Pattern
Aim to land on the ball of your foot when running, as this reduces impact forces and shifts load from the knee to the stronger ankle and calf muscles. This pattern is associated with a smoother, more gentle application of force, which can lower the risk of running-related injuries.
5. Slowly Transition Running Mechanics
When changing to minimalist shoes or a forefoot strike, allow ample time (e.g., 1-3 months) for your feet and ankles to adapt. Start by walking briskly for 30 minutes in minimalist shoes before slowly interjecting short periods of running, to prevent overuse injuries like plantar fasciitis or metatarsal stress fractures.
6. Avoid Forefoot Striking in Conventional Shoes
If attempting a forefoot strike, do so in minimalist shoes. Forefoot striking in conventional shoes can lead to increased plantar flexion, greater load on the Achilles and calf, and increased medial-lateral forces, potentially causing injuries to the Achilles or peroneal tendons.
7. Use Cushioned Shoes for Heel Striking
If you continue to be a heel striker, ensure your shoes have adequate cushioning under the heel. This helps to attenuate the hard impacts associated with heel striking, which can otherwise lead to a quicker application of force (higher load rate) and increased injury risk.
8. Train on Hard Surfaces for Compliance
Incorporate training on hard surfaces to teach your legs to be compliant and attenuate shock effectively. While starting on grass is acceptable, training predominantly on hard surfaces helps develop the necessary leg stiffness modulation for most running environments.
9. Get Fit Before Running
If you are not currently fit, prioritize developing strength and motor control before starting a running regimen. Running without adequate fitness can lead to injuries because your body lacks the muscular control to cushion and manage impact forces.
10. Address IT Band Syndrome Mechanics
If experiencing IT band syndrome, investigate and address mechanical issues such as inward angulation of the thigh, pelvic drop, and internal rotation of the tibia. These factors can excessively stretch the IT band, contributing to pain and inflammation.
11. Be Patient with Gait Retraining
Understand that changing established gait patterns requires significant practice and patience. Utilize feedback (e.g., visual, proprioceptive) to learn correct movements, gradually fade external feedback, and commit to consistent practice over an extended period (months) for lasting change.
12. Gradually Ramp Up Post-Retraining
After completing gait retraining, increase running intensity and distance very slowly. Even with improved mechanics, tissues need time to adapt to new loading patterns, and rushing this process can lead to re-injury.
13. Consider Preventative Gait Training
Even if uninjured, consider gait training focused on landing softer, as studies show it can significantly reduce running injuries (e.g., 62% reduction in novice runners). This proactive approach can help maintain mechanics that keep you below your injury threshold.
14. Encourage Minimalist Footwear for Children
Provide children with minimalist footwear from an early age to allow their feet to develop naturally. This approach supports the development of strong, functional feet, potentially preventing future musculoskeletal issues.
15. Promote Varied Movement & Less Sitting for Children
Encourage children to engage in diverse physical activities and adopt varied postures like squatting or sitting on logs, rather than prolonged sitting in chairs. This fosters physical literacy, core stability, and overall musculoskeletal health, aligning with evolutionary movement patterns.
16. Advocate for Comprehensive Physical Education
Support and encourage daily physical education in schools that includes calisthenics, upper body strength exercises (e.g., monkey bars), and varied movement, beyond just team sports. This helps children build fundamental strength and physical literacy.
17. Encourage Multi-Sport Participation for Kids
Advise children to participate in multiple sports and varied physical activities rather than specializing in a single sport. This reduces the risk of burnout and injury, promoting healthier overall physical development.
18. Develop Protective Foot Calluses
Go barefoot frequently to allow your feet to develop natural calluses. These calluses provide a protective layer against elements, similar to how other animals’ feet are adapted to their environments.
10 Key Quotes
I think that we really evolved to have feet that are very well on their own, well-equipped to be able to walk and run without any kind of support.
Irene Davis
I think it really was because of what I had said to you. There was a number of things coming together with my research, with other people's research that started to make sense to me that maybe we aren't supposed to be in this kind of footwear and maybe this kind of footwear changes the way that we run and maybe we should be trying to strengthen our feet.
Irene Davis
The problem with that is that then you start into the cycle where if you give people cushioning, they actually land harder.
Irene Davis
If you're going to land on your heel, put cushioning under it.
Irene Davis
When you land on the ball of your foot, you shift the load from the quadriceps, the muscle in the front of your thigh and your knee to the ankle and the calf. And when you land on your heel, as a heel striker, you shift the load from the calf to the knee.
Irene Davis
I think that the problem, it starts really, Peter, from when we are children. I would love for you to take a look at a video. There's a trailer on the motivation factor.
Irene Davis
I think we all think that the arch is going to fall and the arch doesn't fall. The arch actually gets stronger.
Irene Davis
The world is your pumice stone.
Chris McDougal (quoted by Irene Davis)
The knee was not really designed to take those kinds of loads in running repeatedly.
Irene Davis
Mechanics, though, is something that's very modifiable. And for a long time, people did not believe that.
Irene Davis
3 Protocols
Transitioning Off Orthotics and Strengthening Feet
Irene Davis- Educate the patient on the approach: The goal is to adapt the body to running, not the shoe to the runner, using analogies like a neck brace to illustrate muscle weakening with constant support.
- Slowly wean the patient from orthotics: Begin by taking them out for short periods (e.g., one hour in the morning) and gradually increase the duration without orthotics. The patient should use their body's soreness as a guide, putting orthotics back in if feet feel sore.
- Simultaneously provide foot strengthening exercises: Implement exercises to build intrinsic foot muscle strength.
- Introduce minimalist shoes for walking: Once the patient can walk comfortably without orthotics in their regular shoes, have them begin walking in minimalist shoes.
Pre-Gait Program for Transitioning to Minimalist Shoes and Forefoot Strike
Irene Davis- Engage in foot strengthening exercises.
- Address any other issues such as hip or knee problems.
- Perform functional activities to teach the patient how to engage their foot intrinsic muscles during movement.
- Incorporate off-treadmill dynamic activities like hopping, lunging, plyometrics, and jump roping to build dynamic movement without actual running.
- Continue this program for 1 to 3 months, adjusting duration based on the individual's age and pain levels, until specific criteria are met before starting treadmill retraining.
Gait Retraining Program
Irene Davis- Conduct treadmill sessions three times a week for four weeks.
- Provide visual feedback (e.g., a monitor displaying impact forces) and instruct the runner to land softer, aiming to reduce or eliminate the impact peak.
- Slowly ramp up running duration during these sessions, progressing from 10 minutes to 30 minutes over the four weeks.
- Follow up with 10 weeks of supervised running outside the lab, with check-ins at two and four weeks.
- Emphasize starting very slow in the initial running phases to allow tissues time to adapt to the new mechanics.
- Note: This program requires significant patience and commitment and is not suitable for individuals with immediate race goals.