Today big brands like Nike, Adidas, Brooks and ASICS are coming forward with new midsole foam materials and construction techniques that promise to give runners higher energy return and therefore help them run faster.
But the question is, is the hype really worth it? Are these new tchnologies really affecting the way we run in some positive way or it’s just in our heads, maybe in the way brands positioned their products in our minds?
How does shoe weight influence our running performance?
It is intuitive and already proven that running with heavier shoes requires a higher energy expenditure than running with lighter shoes. But exactly how that would translate in racing times was never scientifically measured. Until recently, that is.
Researchers from the Department of Integrative Physiology at the University of Colorado Boulder designed a study to measure exactly how much the weight of running shoes affects running times.
They took 18 sub-20 minutes 5K runners and made each participant run on treadmills using three pairs of nearly identical shoes with some differences. Not telling the runners, the researchers added 100 grams (approximately 3.5 ounces) and 300 grams (~11 ounces) of weight to two of the three shoes used during the test by each runner.
Each runner then run treadmill tests in which oxygen consumption and carbon dioxide production were measured.
The treadmill test showed energy cost for the runners rose by about 1% with each 100 grams of extra shoe weight. For the three successive weeks, the runners run instead 3,000 meter time trials on an indoor track. Again, runners run 1% slower for each 100 grams of weight added to the shoe.
Wouter Hoogkamer, the researcher who led the study, said:
elite marathon runners wearing shoes 100 grams lighter than normal could potentially run about 57 seconds faster.
However, when shoe mass is reduced, by compromising cushioning for example, it doesn’t mean you will run faster, said Hoogkamer.
Prior studies in Kram’s lab have shown that proper cushioning also reduces the energetic cost of running. So when selecting footwear, be aware of this trade-off between shoe mass and cushioning.
Springy, lightweight shoes – the answer to all our running shoe questions?
A research published on the Journal of Royal Society Interface in 2016 suggests that while cushioning reduces muscular effort during the impact, it increases activation of foot and leg muscles during push-off – so the benefits of having a cushioned sole to absorb the force of the impact, might be offset by the higher effort required to push off.
What if we could recover some of that extra effort through better energy return?
This is where we stand now. All the new foams introduced by the running companies promise lighter weight, higher energy return – which seems exactly what we need based on these two researches.
This third research, published in 2002 on the Journal of Applied Physiology, concludes that
an increased energy rebound from the compliant surfaces studied contributes to the enhanced running economy.
The real problem is highlighted by the latest research, published this year on the Journal of biomechanics.
Reducing the amount the toes bend by making shoes stiffer can reduce the amount of energy lost. Running shoes with stiffer soles can improve running economy, but only if the bending stiffness is optimised for the specific athlete.
Too stiff and the calf muscles have to work too hard to produce the required forces to rotate the ankle; too soft and the benefit becomes trivial. And this is individually different, runner by runner.
It is not surprising, then that the shoes Nike used for the breaking2 experiment had a differently “tuned” carbon fiber plate for each of the three runners that attempted to break the 2 hour marathon.
The optimal stiffness of a shoe sole varies depending on factors like the weight of the runner, his/her leg length and strength. But an even bigger design problem is that the optimal bending stiffness also varies with constantly changing factors: running at different speeds activates our muscles differently. But a simple spring, such as the carbon fibre blade, cannot change its stiffness for different speeds.
You can read more about this at this source.