Impact Forces Greater in Nike Free than in Pegasus: Why I’m Not Surprised.
A recent study published in Medicine & Science in Sports & Exercise titled Kinematic and Kinetic Comparison of Running in Standard and Minimalist Shoes by Richard Willy and Irene Davis has demonstrated a greater impact force in runners wearing the Nike Free then in the Nike Pegasus. Runner’s World ran a story stating the researchers were extremely surprised by this. I’m not! Here’s why.
The article states that 14 male participants each ran 10 minutes on a treadmill at an 8:00 mile pace while wearing the Nike Pegasus, then again wearing the Nike Free. The runners were all heel strikers accustomed to running in traditional running shoes. The findings have demonstrated an increase in force while running in the Nike Free as the participants continued to heel strike. Davis and Willy apparently hypothesized that the runners would alter their landing in the Nike Free to that of a more natural running gait as a result of the decreased cushion creating “discomfort”. This did not occur. Why? For several reasons. One, the Nike Free is not a minimalist enough shoe to mimic a barefoot gait. There is still cushion present in the heel and the shoe still has the appearance and “feel” of a traditional running shoe. If a person is accustomed to running in a heavily padded shoe, they have adapted a gait that is now “memorized” and second nature for them. They have been in shoes of this type for many years and have forced their body to run this way. It is not as simple as placing a shoe on someone’s foot that has less cushion to change they way they run.
A shoe should allow someone to run, not enable someone to run. Traditional running shoes work against a runner by encouraging them to heel strike with the large cushioned heel. While it is possible to run with a midfoot strike in a shoe like this, it is without a doubt harder. The point of the matter is, by learning to run without a shoe, your form will be more natural and encourage a higher cadence and midfoot strike pattern with a softer landing. The longer one has run inn traditional running shoes, the longer their body has grown accustomed to this and it will be a harder habit to break. Even if you put a “less cushioned” shoe on their foot.
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Far from ‘enabling’ someone to run, walk or engage in any form of locomotion using native motor patterns, all forms of footwear impede the normal coordinated joint function and associated neuromuscular activity while acting as a filter of ground reaction forces. Studies at the Human Performance Laboratory in Calgary, Alberta, Canada that compared barefoot to shod function found that when feet are shod the body attempts to arrive at the least comprised function compared to optimal barefoot function.
Demonstrating the effects of footwear on activities such as running can be problematic because adaptation to the constraint imposed by the footwear usually involves significant changes in gait pattern. For example, elevating the heel in relation to the heads of the metatarsals (heel drop) effectively lengthens the extensor responsible for propulsion.
Conclusively demonstrating that footwear has a negative impact on the lower limbs is difficult in footwear designed for native forms of locomotion. However, it is possible to conclusively demonstrate the effect of footwear in specialized applications such as ice skating. In a paper called, ‘A Novel Protocol for Assessing Skating Performance in Ice Hockey’ presented at the recent ECSS Congress in Barcelona, compared the performance of 5 elite skaters in a number of metrics such as peak force and impulse values in their own (conventional) skates to a new technology. The tests results found significant increases in all metrics, in some cases in excess of 100%. Since the technology only facilitates function of the lower limbs the only plausible conclusion is that the conventional skate impede and limit performance of the user. This protocol in conjunction with more sophisticated instrumentation packages will soon make it possible to isolate the precise mechanism or mechanisms responsible for limiting human performance.