Energy Return is a hot topic in athletic footwear and has even impacted occupational, fashion, and casual shoes. Current foam materials like Boost and EverRun and carbon fiber technologies like the VaporFly 4% and VKTRY insoles promote improved energy return, but is there any science to back this up? Let’s find the truth about energy return…

 

Key Point 1: All foams lose energy. The best energy return foams absorb/lose less energy than their counterparts. There is no shoe that is going to create more energy than our body puts into it.  

 

Key Point 2: Carbon Fiber isn’t typically used as an energy return material.  While carbon is used in the popular Vaporfly 4% and Next% shoes, Nike claims it acts like a lever to minimize wasted energy at the toe joint and optimize ankle position. By reducing wasted energy, runners can be more efficient and possibly perform better. Published research supports this result, but there is no consensus on the exact mechanism for improving running economy. 

 

Key Point 3: Shoes with higher energy return on mechanical “ball drop” tests won’t work for everyone. ASTM’s own description of the test states results, “… may not correlate with similar values experienced by a runner’s heel or foot.”

 

Key Point 4: Foams with higher energy return feel good to some people. This has more to do with the “fast recovery” of the foam in-between steps, the opposite of what we observe in memory foams. For this reason, Heeluxe supports the use of fast recovery/’energy return’ foams in footwear. 

The allure of “energy return” is understandable, but it’s too damn difficult for a foam or carbon piece to create. The godfather of modern biomechanics, Benno Nigg, summarizes useful energy return as:  (1) large enough to make a difference; (2) energy returned at the right time; (3)energy is returned at the right frequency; and (4)energy is returned at the right location. No ‘energy return’ shoes perform this function. 

Instead of calling this new wave of shoes as “energy return”, let’s label them correctly as “reducing energy loss.”  Or let’s create entirely new wording until we can create honest, true energy return. 

 

While you’re working on real energy return, let us know if you’d like to hear more about current foam technologies or test different foams in your shoes by contacting [email protected]