Cutting the soles of running shoes is a time-honored, old-school running habit. Runners would slice small lateral grooves into shoes they felt weren't flexible enough for their feet. They found that making the cuts made some shoes more comfortable because doing so allowed the foot to flex more naturally as they ran on large, cushioned mid-soles. To improve traction, comfort and foot flexibility, the practice of cutting soles has gone "new school" and is being embraced today by many shoe manufacturers.
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Look at a dog's paw. That's what shoemaker Paul Sperry did after after nearly losing his life on a slippery boat deck; he then spent years trying to create a non-slip boat shoe. One day Sperry noticed his cocker spaniel, Prince, run effortlessly over a patch of ice. He took note of the cracks and lines on Prince's paw and that became the inspiration for the famous Top-Sider boat shoes. Sperry patented a process called Razor-Siping, which entails cutting thin lines into the soles of shoes so they provide better traction. Runners, especially trail runners, have also been known to retrofit their own shoes with micro-cuts if they need improved traction.
Some runners insist that making a running shoe more flexible by cutting lines in the sole also makes it much more comfortable. One running shoe store even provides the service of retrofitting shoes by slicing the soles, if customers desire. Other runners, however, say that cutting the sole can shorten the life of the shoe and, possibly, negatively affect the stability control built into the mid-soles of some shoes.
The Razor-Siping technology is used to make soles with better traction for both wet recreation, such as kayaking and running, and dry land sports such as running. Razor-Siping in minimalist shoes mimics the soles of your own foot's sole, which is lined exactly like hands and fingers with the swirls and loops of prints. The popularity of minimalist running shoes has put Razor-Siping technology into the spotlight as something more than an odd tendency by some runners to loosen up the flexibility of their shoes. Companies, such as Vibram FiveFingers, have taken the technology further to make minimalist models for cold weather running.
The most dramatic illustration of how runners cut the soles of their shoes to achieve greater flexibility and comfort through a model made by Nike. With flex grooves cut almost completely through the sole and coming close to the bottom of a runner's foot, the Nike model is "designed to maximize the foot's natural range of motion while providing protection and cushioning for a smooth ride."