Changes

* '''Weight'''. Probably the most critical feature of the shoe is its weight, as relatively small increases in the weight of the shoe create a surprisingly large increase in the effort it takes to run. A general estimate is that each 3.5oz/100g increases the effort by 1%.

* '''Cushioning'''. While cushioning does not appear to be effective at reducing impact, [[The Science of Running Economy]] indicates that cushioning can reduce the effort it takes to run. In addition, I found that the highly cushioned shoes I refer to as [[Minimax]] can reduce how sore my feet become on ultramarathons. However, cushioning and weight, so the right shoe for you will be the right balance of cushioning and weight. The best shoes provide the highest level of cushioning for their weight. Cushioning comes from the combination of the thickness and firmness of the midsole. The shape of the midsole can also make a difference, as a flat bottomed midsoles has less cushioning than a "egg crate" shaped midsole. The insole can also make a difference to the cushioning.

* '''Longevity'''. How long a shoe lasts normally depends on the foam midsole. In shoes where the foam midsole is not covered by a hard rubber outsole, the life of the shoe is typically limited by how quickly the midsole wears away due to abrasion from the ground. Different types of foam have at differing levels of abrasion resistance. If the midsole is covered by a hard rubber outsole, and the life of the shoe is typically limited by how quickly the foam breaks down and loses its shape and cushioning. There are some minimalist shoes like the Merrell trail glove that have little or no midsole, in which case the life of the shoe is limited by how long the outsole lasts. These shoes typically lost vastly longer than the cushioned counterparts. The table below is a rough guide to how I assign longevity numbers, though obviously these are tweaked for specific shoes.

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