As I was lacing up my running shoes the other day, I realized it was time to buy a new pair. While they weren't that old, the tread on the outside of the sole was completely worn down. Small holes above where my pinky toes rested inside the shoe had begun to develop. My running shoes were telling me that my underpronation had gotten the best of them – again.
Underpronation (also called supination) is the insufficient rolling-in motion of the foot when it hits the ground. As part of a normal stride, the foot will roll slightly inward after the heel hits the ground (pronation). This cushions the impact and helps you adapt to uneven surface.
A normal foot pattern rolls inward at around 15% during your stride. When you supinate, your foot rolls in under 15%. Conversely, overpronation is defined as the inward rolling of the foot over 15%.
In plain terms, supination means your foot rolls out during your stride. That's why the outside tread of my running shoes was smooth while the rest of the tread was fine. Every time my foot hit the ground, it didn't pronate sufficiently (roll in), and the majority of my weight stayed on the outside edge of the foot. This forced the pinky toes to hit the mesh upper and eventually poke through.
Underpronation is less common than overpronation. While less than 10% of the population suffers from true supination, it still causes many people problems.
Who Underpronates and Why?
There are three main characteristics of people who underponate or supinate.
- People who underpronate are often heel strikers – their heel hits the ground first. Then, the foot rolls out, and the force of their body weight is unevenly distributed to the outer edge of the foot
- Underpronation is more common in – but not exclusive to – people with high arches. High arches are often more rigid and less flexible. When your foot hits the ground, your arches don't sufficiently flex to accommodate dynamic movement.The force of the stride then pushes the weight towards the outside of the foot.
- Tight calves and achilles tendons magnify the movement of supination. The tightness in the back of the heel and up the leg pulls your foot outwards when it lands. If tight calves and achilles tendons are the cause of your supination, stretching is an easy solution.
Injuries Associated with Supination
Like any biomechanical irregularity, underpronation can cause specific injuries. Common injuries associated with supination include:
- Plantar fasciitis – it may seem that no matter how you walk or run, the inflammation of the plantar fascia (or plantar fasciitis) that runs along the bottom of the foot is a common injury. For people who supinate, the plantar fascia remains rigid, absorbing too much weight too quickly during the stride.
- Ankle sprains – because the impact of your stride is concentrated on the small outside portion of the foot, you are more likely to roll the ankle outward.
- IT band syndrome – as the weight remains on the outside of your foot, it travels up your legs. This can cause inflammation and pain in other areas, particularly on the outer thigh and knee. The iliotibial band, which runs down the outside of your quadricep, can become tightened and inflammed.
- Achilles tendinitis – your achilles tendon will try to stabilize your ankle and foot. The excessive outward rolling can cause it to become inflammed.
- Stress fractures – supination is connected to improper shock absorption. Especially for runners, when your bones experience a repetitive application of force that is not properly and evenly absorbed, you can develop small fractures.
Neutral Shoes and Shock Absorption
If you underpronate, you need to find shoes that accommodate your gait. Because the body weight is not distributed evenly across the foot, forces of impact remain concentrated on the outside of the shoe. When you push off, your smaller toes do most of the work. This is both inefficient and lessens your ability to properly absorb the impact of your stride. Most specialists recommend finding neutral shoes with extra cushion or shock absorption qualities.
Other characteristics you should look for in a shoe include:
- Shoes with curved lasts to allow for pronation
- Lightweight trainers as they allow more foot motion
- Shoes with flexible medial (inner) sides
Insoles and Underpronation
If biomechanics (and not tight calf muscles) are the cause of underpronation, you will need to go above and beyond buying a pair of neutral, shock-absorbing shoes. Most shoes do not sufficiently support high arches. Thus they won't correct the underlying cause of your underpronation. Because having high arches is closely correlated to supination, you need to find insoles that will support the arch during your stride. Tread Labs Stride fully supports the arch, preventing your foot from rolling out. It also stabilizes the heel with a deep heel cup, which concentrates the fatty pad underneath your heel bone. This acts as extra shock absorption. With the proper insoles, you can correct supination, prevent injury and develop a more efficient stride.