Better Performance with More Cushioning?
A study of Tung et al, « A test of the metabolic cost of cushioning hypothesis during unshod and shod running » has been recently published in Applied Sciences
Authors attached 10- and 20-mm-thick slats of the same foam cushioning used in running shoe midsoles to the belt of a treadmill that had a rigid deck. Twelve 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. Compared to running unshod on the normal belt, running unshod on the 10-mm-thick foam required 1.63% ± 0.67% (mean ± SD) less metabolic power (P = 0.034) but running on the 20-mm-thick 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. Conclusion: On average, surface and shoe cushioning reduce the metabolic power required for submaximal running.
This study was not yet published but we have known it for a few months because it has been presented in a conference as a poster some months ago. The results are consistent with the study from Kram et al. at the University of Colorado, that have shown reductions in O2 consumption of 8 midfoot strikers (out of 12 subjects) when wearing shoes with low cushioning (minimalist shoe of 70% TRC rating) compared with barefoot. This study got rid of the shoes (mass and interference effects) to isolate the effects of cushioning.
Here are some interesting points:
- Individual responses were observed. On a 20mm cushioning surface, 5 subjects were less economical, and 7 were more economical in comparison with running on rigid carpets without foam.
- Among all conditions, barefoot running on a low cushion surface (10mm foam, which is comparable to very minimalist racing flats) was more economical.
- The majority of runners become less economical with more cushioning on the treadmill (20mm compared with 10mm)... even if this cushioning is not included within running shoes, that would add a mass effect. Would it be even less economical with 30mm of cushioning, which represents 85% of all the running shoes on the market?
- Wearing running shoes (even a TRC rating of 70% - Nike Free 3.0) was the least economical condition, significantly less than barefoot on a 10mm foam surface treadmill. Moreover, shoes caused a decrease in step frequency and ground contact time. Would its 4mm drop, its 21mm cushioning, its 211g (7.4oz) weight or simply the interference between foot and ground be responsible?
- Study limitations: limited external validity (applicability to the population of runners) due to the inclusion of midfoot strikers (less than 10% of all runners); Only 2 foam thicknesses were tested (despite the fact that most running shoes available on the market have around 30mm of stack height).
This study is interesting, but a lot of work is still needed to determine enhancing conditions for O2 consumption and performance improvement. This is a small experimental 12 subjects study. Personal critique: Dr Kram is well renowned in the field of runners physiology and let's not question his integrity. However, the fact that he's being a paid consultant for Nike seems somewhat annoying to us...