To Cushion or not to Cushion, that is the Question

All runners love cushioned shoes, right? If you don't, then you're probably still stuck in that toe shoe or minimal running fad. The truth is, those minimalists might have been on to something.

Highly Cushioned Shoes

A recent study outlines why running in highly cushioned shoes can result in stiff legs and amplified impact loading. Running shoes are designed to manage and reduce impact loading and injuries resulting from the constant impact of running. However, a study by Juha-Pekka Kulmala, et. al. found that shoes that are highly cushioned alter our natural running mechanism and actually amplify impact loading! Before you go ask for a refund on your shoes, this study also found that the outcome was more pronounced at faster paces.

At about 9 mph (or 6:30 minutes/mile) the ground reaction force impact peak rate was 10.7% greater in a high-cushioned shoe, and the loading rate was 12.3% greater. The researchers attributed the greater impact loading while using the high-cushioned shoes to a stiffer leg during the landing phase of the running gate compared to a conventional shoe.

This is a pretty amazing find! Humans maintain the same bouncing movement of the body's center of mass across surfaces that have different stiffness. We adjust for this by stiffening our legs. For example, if you go from pavement to softer dirt, your leg becomes stiffer and compresses less to maintain the same movement of your center of mass. And you don't even have to think about it; pretty cool!

What is a "Highly-Cushioned Shoe"

As pointed out, the results will vary with speed. In the study, the researchers used the Hoka Conquest running shoe as the high-cushioned shoe, and the Brooks Ghost 6 running shoe as the conventional shoe. The basic idea was that the highly-cushioned shoe changed the spring-like mechanics of running we naturally have. At higher speeds the mechanic is thrown off even more, but there was still a discrepancy at lower speeds.

There was one more interesting result. The total body center of mass vertical oscillation was worse in the conventional shoe at slower speeds. This means the lowest point of the ground contact to the highest point of the flight phase of the runner's gate showed a speed dependent response. Running slower showed less oscillation in the highly-cushioned shoe where running faster showed more oscillation. Running speed, then, can significantly influence the way runners adapt to different cushioning in shoes.

The Take-Away

1. More shoe cushion is not always better for those who want to run more.

2. Running speed significantly influences the way runners adapt to different shoes. The results seem to shoe that it is a good idea for runners to train in racing flats (low-cushioned shoes) at higher speeds. Contrary to popular belief, this seems to reduce impact related injury.

3. Highly-cushioned shoes can cause your natural stride to change and lead to more injury.

4. This doesn't mean that you should never by highly-cushioned shoes. It seems this would only be relevant for the runners out there looking to put in mileage at a faster pace (above 7 min/mile pace).