Running Shoes and Economy of Running

The effect of the type of running shoe as well as running technique on economy of running has obviously been of interest in recent years. It can often be a trade-off between the weight of a shoe; the energy return from the shoe; and the increased muscular effort to midfoot or forefoot strike (and the surface being run on will also factor in as well). Up until recently, most of the studies were showing mixed results on the effects of running technique and shoes on the metabolic cost of running. More recently, a pattern is emerging. I have reported on a number of studies as they come out.

I even got accused of cherry picking by a fan boy who just did not like the results of a study that found economy between forefoot vs rearfoot striking was no different. I don’t cherry pick, I report them all! All the studies that have been released this year have generally found no generic differences in running economy between forefoot vs rearfoot striking or minimalist vs traditional running shoes.

Probably, and intuitively, the response to these variables is going to be specific to the individual rather than a generic one type of shoe or running form is more economical than another. This will depend on things such as the individual variation in joint axes positions that affect lever arms of tendons and the subsequent amount of muscular needed to complete a certain action as well as things like being in the preferred motion pathway (ie Nigg’s work on soft tissue vibrations) and running surface energetics.

Now we have another paper published on the economy of running and shoes to add into the mix:

A Test of the Metabolic Cost of Cushioning Hypothesis during Unshod and Shod Running
Tung, Kryztopher D.; Franz, Jason R.; Kram, Rodger
Medicine & Science in Sports & Exercise: 25 July 2013
Purpose: To investigate the effects of surface and shoe cushioning on the metabolic cost of running. In running, the leg muscles generate force to cushion the impact with the ground. External cushioning (surfaces or shoes) may reduce the muscular effort needed for cushioning and thus reduce metabolic cost. Our primary hypothesis was that the metabolic cost of unshod running would decrease with a more cushioned running surface. We also hypothesized that due to the counteracting effects of shoe cushioning and mass, unshod running on a hard surface would have approximately the same metabolic cost as running in lightweight, cushioned shoes.

Methods: To test these hypotheses, we attached 10 and 20 mm thick slats of the same foam cushioning used in running shoe midsoles to the belt of a treadmill which had a rigid deck. 12 subjects who preferred a midfoot strike pattern and had substantial barefoot/minimalist running experience ran without shoes on the normal treadmill belt and on each thickness of foam. They also ran with lightweight cushioned shoes on the normal belt. We collected V[spacing dot above]O2 and V[spacing dot above]CO2 to calculate the metabolic power demand and used a RMANOVA to compare between conditions.

Results: Compared to running unshod on the normal belt, running unshod on the 10mm thick foam required 1.63 +/- 0.67% (mean +/- SD) less metabolic power (p=0.034) but running on the 20mm foam had no significant metabolic effect. Running with and without shoes on the normal belt had similar metabolic power demands, likely because the beneficial energetic effects of cushioning counterbalanced the detrimental effects of shoe mass.

Conclusions: On average, surface and shoe cushioning reduce the metabolic power required for submaximal running.

The results of this study can be a little difficult to comprehend and interpret, so here is the authors discussion:

In this study, we tested the metabolic cost of cushioning hypothesis which states that running involves a “cost of cushioning” the body against impact. Specifically, we quantified the isolated effects of shoe cushioning on the metabolic cost of running, while controlling for footstrike pattern, barefoot/minimalist running experience, and footwear. Supporting our first hypothesis, we found that on average the metabolic cost of unshod running was significantly reduced when subjects ran on a 10 mm foam cushioned surface compared to a normal rigid treadmill surface. Supporting our second hypothesis, on the normal, rigid treadmill surface, the metabolic cost of unshod running was not significantly different from running with lightweight, cushioned running shoes. To further clarify, our first hypothesis stated that the metabolic cost of unshod running would decrease with a cushioned surface. While 10 mm of surface cushioning did elicit a lower metabolic cost than the rigid treadmill surface alone, 20 mm of surface cushioning would decrease with a cushioned surface. While 10 mm of surface cushioning did elicit a lower metabolic cost than the rigid treadmill surface alone, 20 mm of surface cushioning
did not on average further reduce metabolic cost. We suspect that there may be an optimal cushioning thickness for each individual which minimizes their metabolic power demand. This optimum likely depends on many factors including cushioning hardness (durometer), body mass, and footstrike preference.

In summary, we found that a moderate thickness of foam cushioning generally reduced the metabolic cost of running. Additionally, the metabolic cost of running did not differ between unshod and shod conditions, presumably because the positive effect of cushioning were counteracted by the negative effect of shoe mass

Thus, it appears that the positive effects of shoe cushioning counteracted the negative effects of added mass, resulting in a metabolic cost for shod running approximately equal to that of unshod running.

Of special note to me was this sentence in the results section:

We did find considerable individual variation with respect to the effect of
surface cushioning on metabolic demand

…which emphasizes the point I started with above on subject specific response to the variables involved in determining running economy. There is no one size fits all.

As always, I go where the evidence takes me until convinced otherwise, and this evidence supports that the hypothesis that the response to cushioning in a running shoe is probably going to be subject specific.

Tung, Kryztopher D.; Franz, Jason R.; Kram, Rodger (2013). A Test of the Metabolic Cost of Cushioning Hypothesis during Unshod and Shod Running Medicine & Science in Sports & Exercise DOI: 10.1249/MSS.0b013e3182a63b81

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