What exactly is energy return? Here's your 5-minute guide to becoming a running shoe expert
When it comes to choosing a pair of running shoes, it can be tricky to understand exactly what people (and by people, we mean us) mean by the terms ‘midsole’, ‘energy return’ and ‘drop’.
So, to help you learn the language of running shoes, we’ve broken them down by their three main component groups below. Let’s start at the top and work down from upper, to midsole to outsole.
Shoe jargon 101
Last: The last is a manufacturer’s model that mimics foot shapes. There are three kinds: curved, semi-curved, and straight. Racing shoes are typically curved for arch support. Stability shoes are usually straight for motion control. The majority of shoes are semi-curved.
Heel-to-toe drop: Also called drop or offset, this is the difference in height between the forefoot and heel. Most shoes are 8mm to 10mm. A zero- to 4mm-drop platform renders a more natural foot position. But most runners find a higher lift more comfortable, and some feel tightness in their tendons or muscles when changing from a higher to a lower heel lift.
Energy return: This is the amount of bounce or spring inside the shoe after your foot lands on the ground. A higher percentage gives you a bouncier feeling; however, other factors affect a shoe’s responsiveness, dependent on the individual, including the runner’s weight, gait, and form.
Stability: Tech built into a running shoe to assist runners who overpronate – meaning their feet roll too far inward during their stride.
The upper
The upper covers your foot to ensure a snug, secure fit while providing stability.
Upper Fabric: Usually made of engineered mesh (patterned for strength and flexibility) or knit that provides a close-to-foot, sock-like feel.
Overlay: This layer, or layers, of fabric provides structure to the upper and is often made of reflective materials for visibility. They may include the shape of the brand’s emblem. More shoes are forgoing overlays to reduce weight.
Tongue: The tongue protects the top of your foot from the laces and is usually connected to the upper near your toes, though there are two variations: a gusseted tongue connects to the upper on its sides to keep debris out and conform to your foot more securely, but it’s more difficult to get on and off your foot. A ‘burrito’ tongue – only connected on one side – is easier to put on and take off than the gusseted type.
Toebox: Protects the toes and should provide ample room for them to splay, preventing toes from rubbing and blistering.
Heel counter: A plastic or fabric piece that cradles the heel and provides side-to-side support. It can be internal or external.
The midsole
Composed of rubber-like foam, the midsole is the core of the shoe and provides cushioning and energy return. Different brands will use different types of foams:
EVA: Ethylene vinyl acetate has been the standard in midsole foams for its softness, flexibility, and low production cost since the 1970s. The downside is that it becomes more rigid in cold weather and compresses over mileage, losing its bounce.
PU: Compared with EVA, polyurethane is less sensitive to temperature, is more durable, and has a bouncier feel. However, PU is roughly 50 per cent heavier than EVA.
TPU: Thermoplastic polyurethane is heated and reformed. Companies like Adidas and Saucony use a two-step process, making TPU beads and then fusing them to create a more durable, flexible, and bouncier foam than EVA and PU. However, TPU is still a heavier foam compared with EVA.
Pebax: Polyether block amide gained recognition as the highly responsive foam used in the Nike Vaporfly. Pebax retains its flexibility and energy return in cold conditions and is 20 per cent lighter than TPU.
When you may need a specialised insole
Not every runner needs an orthotic insole (aka sock liner or insert), says Dr Jordan D. Metzl, a New York City-based sports medicine physician. ‘There is no evidence that every person with a certain type of foot needs a correction.’
For example, not all flat-footed runners overpronate and need extra stability. However, if persistent injuries – shin splints, stress fractures, plantar fasciitis – won’t pass, give an orthotic a test run. And don’t forget to take out the shoe’s insole first.
The outsole
The outsole is the bottom of the shoe, usually made of solid rubber or blown (air-injected) rubber, or a combination of the two.
Solid rubber is more durable, whereas blown rubber – usually located in the forefoot – is more flexible and adds to the cushioning of the shoe. Depending on whether the shoe is meant for the road or trail, the outsole will either be highly segmented (a flatter tread with flex grooves) for smoother transitions on pavement or have a more aggressive lug pattern for grip on rugged terrain.
Footbridge: Located between the heel and forefoot. It provides stability by reducing twisting.
Bevelled heel: A heel that’s rounded, or angled, in the back to lessen heel impact and allow you to land smoothly.
Rock plate: Made of plastic typically, these protective pieces are placed between some trail shoes’ midsole and outsole for extra defence on rocky, rooty trails.
Decoupled heel: A split heel that absorbs shock and provides a smooth transition when the heel lands on the pavement.
Stability technologies
Medial post: A wedge of firm foam located below the ankle bone, in the shoe’s midsole. It’s made out of a denser material, usually EVA. The post changes the distribution of force underneath your foot as you run, reducing the stress on your ankle and causing your foot to roll inward less.
Guide rails: Plates located on the sides of the shoe, inside the midsole. The guide rails couple the heel’s rotation with the knee’s (meaning the ankle’s and knee’s rotation sync with each other), thus providing support and making the runner more efficient.
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