The science of the ‘Goldilocks’ principle of footwear cushioning.

Tags: foot, foot function, Science

“The best investment is in the tools of one’s own trade”
Benjamin Franklin

Sensory feedback from the soles of the feet is important for both injury avoidance and movement efficiency (Robbins, Gouw and Hanna, 1989; Tung et al., 2014), but human feet are vulnerable and themselves need protection. Unlike other running mammals, humans did not evolve hooves or thick pads to prevent puncture or thermal injury. It is no surprise, therefore, that footwear use has a long history dating back some 10,000 years (Pinhasi et al., 2010). In our evolution as endurance-running specialists, barefoot has rarely been a strategy of choice. Even so-called ‘natural’ running tribes like the Tarahumara of Mexico and the hunter-gatherers of Africa wear their own versions of thick-soled sandals to protect their feet from heat and the rough-natural terrain (Lieberman, 2014).

Too little, too much and ‘just right’.

Reducing sensory feedback from the feet impairs movement patterns, with avoidance of numb areas, increased pressures under sensate areas and increased lower-limb muscle activity (Nurse and Nigg, 2001). Conversely, too much sensory stimulation of the foot triggers pain, also impairing movement patterns (Levins et al., 1998). An ingenious study using grades of cushioning foam strapped to the slats of a rigid treadmill showed running economy was worse when barefoot without cushioning, improved with 10mm of cushioning foam and worsened again with 20mm of cushioning to values similar to no cushioning (Tung et al., 2014). Impaired economy with no and with 20mm of cushioning was attributed to additional muscular work of cushioning landings with no protection, and stabilising the foot and lower leg with too much cushioning. For running economy and movement efficiency, there is a sweet spot for cushioning and the resulting sensory feedback, just as Goldilocks discovered with the beds of the bears.

There is no single sweet spot.

The optimal feedback and cushioning required for comfortable and economical running varies with the running surface, but the need for protection from thermal and puncture wounds is constant. As such, the use of footwear with cushioning appropriate for the running surface is a sensible strategy with a long history and a solid basis in science. If running is your trade, investing in appropriate tools for the task is a smart move.

References.

  • Levins AD, Skinner HB & Caiozzo VJ. (1998). Adaptive gait responses to plantar heel pain. Journal of Rehabilitation Research and Development 35(3), 289-293.
  • Lieberman DE. (2014). Strike type variation among Tarahumara Indians in minimal sandals versus conventional running shoes. Journal of Sport and Health Science 3, 86-94.
  • Nurse MA & Nigg BM. (2001). The effects of changes in foot sensation on plantar pressure and muscle activity. Clinical Biomechanics 16, 719–727.
  • Pinhasi R., et al. (2010). First direct evidence of chalcolithic footwear from near eastern highlands. PLoS ONE. 5: e10984.
  • Robbins S, Gouw G, & Hanna A. (1989). Running-related injury prevention through innate impact-moderating behaviour. Medicine and Science in Sports and Exercise 21, 130–139.
  • Tung KD, Franz JR & Kram R. (2014). A test of the cost of cushioning hypothesis during unshod and shod running. Medicine and Science in Sports and Exercise 46(2), 324-329.

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