Running Biomechanics
Gait Cycle - the progression of the foot as it heel strikes (phase #1), rolls to mid foot (phase #2), then to toe-off (phase #3)
3 Phases of the Gait Cycle:
- Heel Strike
Running is a "High Impact" activity, meaning that at some point, both feet are off the ground. How much impact? Wanna Guess? A runner comes down with 3.5 times his/her body weight. What does our body need to do with that shock? Absorb it! Cushion it! Dissipate it! Disperse it! If we don't, it travels back up the legs, causing injury.
- Mid foot phase
What do we have in the midfoot? (The arch!)
3 Types of Arches:
- Flat - flat arches are extremely flexible and require a great deal of control
- Medium - neutral arch is ideal and requires a degree of stability
- High - high arches are extremely rigid and inflexible and require little if any control
- Toe-off
The toe-off tells us what type of pronator a runner is. Most runners will look at the bottom of their running shoes and conclude that they wear out the outside of their shoe because the outside heel is worn. From this, they may conclude that they need a cushioning shoe. Most are wrong! Everybody wears out the outside heel. It's the wear pattern at "toe off" that will determine your rate of pronation, and therefore the type of shoe you should be running in.
What is pronation?
Pronation is the natural, inward roll of the foot; pronation begins when the heel contacts the ground, the foot then rolls inward to absorb shock and transfer weight to the ball of the foot as it prepares to push off. It is a natural and necessary motion for running and walking.
There are three types of pronators:
- Overpronator - The excessive inward roll of the foot. A flat foot absorbs a lot of shock. It's very flexible and needs support. Motion control shoes work best for overpronators. We use the
 symbol for our shoes that offer motion control.
- Neutral pronator - The foot pronates naturally. Mild pronators disperse shock effectively. A medium arch absorbs shock moderately. Stability shoes work best for the neutral pronator. The
 symbol is for stability.
- Underpronator (Supinator) - the lack of sufficient inward motion of the foot. A high arch absorbs less shock. Cushioning shoes that are highly flexible are best for the underpronator.
Only a small population truly underpronates.
For the three types of runners, there are three types of shoes:
1) Motion Control - built for the overpronator
2) Stability - built for the moderate pronator (nuetral foot)
3) Cushion - built for the underpronator or supinator
Next thing we need to know about the shoe is what shape is it? If we think about the medial (inside) edge of the shoe as a steering wheel, what direction is a straight shoe steering the foot in? What direction is a curved shoe steering the foot in?
Three types of shoe shapes:
- Straight - shape found in motion control shoes built for overpronators
- Semi-curved - shape found in stability shoes built for mild pronators
- Curved - shape found in cushioned shoes built for underpronators
Last thing to know is the construction:
There are three types:
1. Board - Cardboard piece in shape of footbed that adds stability
- Purpose of a board last: Provide full length support (not common in running shoes) (Anyone have a bad back? Anyone ever put plywood under a mattress or know someone who does? Why? To provide support. Same concept as Board/Combination lasts)
2. Combination - Half board in heel, half soft, moccasin like construction in forefoot
- Purpose of combination last: Provides stability in the heel and support in the midfoot
3. Slip - entire footbed is built like a moccassin to promote flexibility
- Purpose of slip last: Provides flexibility
There are shoes designed for heavier weight runners and shoes designed for lighter weight runners.
- Average male weight 165-180 - anything below range is considered a lightweight runner, anything above is considered a heavy weight runner
- Average women's weight 125-150 - anything below range is considered a lightweight runner , anything above is a heavy weight runner
Shoe Materials:
Shoe is made up of three parts:
- Upper
- Midsole
- Outsole
1) Upper: Holds the foot in place, protects the foot from rocks and dirt, has synthetic leather for durability, mesh for breathability and reflective material for safety.
2) Midsole: Most important part of shoe. There are three materials that make up the midsole:
- EVA - lightweight, foam-based cushioning
- Dual-density EVA:
- What happens when you double the density of something? It gets stronger, firmer, heavier (twice the mass in the same amount of space)
- We call this dual-density EVA a "medial post"
- Medial - because it is on the inside of the shoe
- Post - because it has a beginning and an end. The length of the post determines the amount of control
- Polyurethane:
- very durable cushioning
- More durable/stable than EVA, weighs more than EVA.
3) Outsole: Has tread for traction, flex grooves for flexibility, protects from dirt and rocks. Made of two materials:
- Carbon rubber (durable - same material as tires)
- Blown rubber (lighter, more flexible, more cushioned, not as durable). Blown rubber is rubber with air
injected into it (blowing a bubble with chewing gum)
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