Shoe Cushioning Influences the Running Injury Risk According to Body Mass: A Randomized Controlled Trial Involving 848 Recreational Runners.

There's a longstanding assumption in running shoe design that softer cushioning protects runners from injury, and that heavier runners in particular need more shock absorption. This trial tested that idea directly by randomly giving 848 recreational runners one of two otherwise identical shoe prototypes, differing only in how stiff or soft the midsole cushioning was, then following them for six months to track running-related injuries. Overall, runners in the harder shoes had a higher injury risk than those in the softer shoes. But when the researchers split runners by body mass, the protective effect of softer cushioning only showed up in lighter runners, not heavier ones.

This challenges the common belief that heavier runners need firmer or more cushioned shoes to stay safe, and suggests body mass alone doesn't predict who benefits from extra cushioning. The main limitation is that this involved only two specific shoe prototypes and one injury definition, so the findings may not generalize to all footwear or runner populations.

If you've ever been told that heavier runners need extra-cushioned shoes to avoid injury, this study is worth knowing about. Researchers gave 848 recreational runners one of two versions of the same shoe, one softer and one firmer, and tracked injuries over six months without either runners or researchers choosing which shoe someone wore. Overall, runners in the firmer shoes were more likely to get injured than those in the softer shoes.

But interestingly, this protective effect of soft cushioning only appeared clearly in lighter runners. Heavier runners didn't show a statistically significant difference in injury risk between the two shoe types. This pushes back against the common assumption that heavier runners specifically need more cushioned shoes.

It suggests body mass by itself may not be a reliable guide for choosing shoe cushioning. That said, this was one trial using two particular shoe designs, so it can't tell us how these findings apply to the huge variety of running shoes actually on the market.

This is a summary of research, not medical advice. Talk to your own healthcare provider about anything affecting your care.

This trial speaks to a common clinical assumption: that runners with higher body mass need more cushioned footwear to reduce loading-related injury risk. The study randomized 848 recreational runners to one of two shoe prototypes differing only in midsole stiffness (soft, 61.3 N/mm, versus hard, 94.9 N/mm) and followed them for six months for injuries defined as complaints reducing or interrupting running for at least seven days. The primary finding was a statistically significant increase in injury risk with the harder shoe overall (subhazard rate ratio 1.52, 95% CI 1.07-2.16), while body mass itself was not associated with injury risk.

In a stratified subgroup analysis, the protective effect of softer cushioning held only for lighter runners (SHR 1.80, 95% CI 1.09-2.98), not heavier runners (SHR 1.23, 95% CI 0.75-2.03), where the confidence interval crossed one. For practice, this means the intuitive heuristic of matching cushioning to body mass is not supported here, and the subgroup result, while informative, is exploratory relative to the trial's primary comparison. Confidence should be tempered by the fact that this examined two specific prototypes and one injury outcome definition, so extrapolation to commercial footwear or other injury types is not established.