A Closer Look At Minimalist Running Shoes
Examining The Reality Behind Reduced Cushioning
As shoes became more and more cushioned between the 1970s and the 2000s, the midsole thickness increased. Consumers likely gravitated toward increasingly cushioned shoes because of the comfort benefits of cushioning. The softer midsole materials and elevated platform do cause some significant differences in kinematics and balance in comparison to barefoot conditions.
The marketing. By reducing the cushioning, companies says minimalist shoes can promote a “more natural foot strike” and enhance proprioception.
The science. Midsole cushioning does reduce transient shock impacts and peak plantar pressures.9 Research has shown plantar and midsole footwear characteristics to facilitate pronation and negatively affect balance.10-14 Multiple studies have shown that frontal plane motion is greater with conventional shoes in comparison to the barefoot condition. One study showed that balance is negatively affected even with a thin sock in comparison to being barefoot.12 In addition, neuromuscular coordination strategies and limb stiffness are affected by the amount of cushioning in shoes.15,16
The dilemma. Nigg and colleagues have referred to shoes as filters. They filter the sensory input to the plantar foot.7 A very simple way to describe the differences between conventional running shoes and minimalist shoes is that they are different filters. As runners do not respond in systematic ways to biomechanical interventions, the key question becomes: how much cushioning (or filtering) is too much or too little for any given individual? Certainly, manufacturers should not be claiming that their particular designs are optimal for all runners in terms of running form, pronation and balance. As for proprioception, minimalist footwear cannot enhance proprioception as some claim. Minimizing the amount of material between the foot and the ground will likely have less of a negative effect on proprioception but certainly not enhance it.
A Critical Look At Reduced Shoe Mass
The marketing. Reduced shoe weight decreases the metabolic energy cost of running.
The science. Frederick has previously reported that the metabolic cost of shoe weight is approximately 1 percent per 100 grams so there does appear to be a cost of the weight of the shoe.17 However, some researchers have found that the difference is not always statistically significant and the differences of shoe mass do not fully explain the differences in running economy. Only three of eight gait studies showed increased economy that was significant and/or consistent with benefit of decreased shoe mass.2,18-23 Some have speculated that inhibited elastic energy storage and return in soft tissue or energy absorbed by midsole cushioning material may also play roles in decreased running economy.18-20 In Franz’s study, eight of 12 test subjects were more efficient in lightweight shoes (5.4 oz) than barefoot and that energy cost was 3 to 4 percent lower in the shoes than barefoot.24
The dilemma. There is some controversy in that many of the studies showing reduced energy cost occurred in lab settings on runs of shorter duration. Questions still arise about energy cost savings over the duration of longer events such as marathons. Franz’s study suggests that decreased cushioning may increase the workload of muscles and therefore increase energy cost.24 There may be some muscle energy benefits to some cushioning but as would be expected, the optimal amount of cushioning is likely highly unique to each runner and would be affected by such variables as duration of run, pace, surface characteristics and even the level of fatigue.