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From Fellrnr.com, Running tips
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* '''Familiarity'''. There is reasonable evidence that runners will adapt based on their training, something that makes intuitive good sense. Part of that adaptation is to the shoes that are normally worn, so any radical change in shoe design can be disruptive, and possibly lead to injury. This is particularly true when moving to a more minimalist running shoe. Therefore, if you're looking for running shoe that is radically different to what you use too, it would be prudent to migrate through intermediary types of shoe. For instance, if you reduced to running in a traditional running shoe, but want to move to a zero drop shoe, you could use the [[Saucony Kinvara]] has a half-way house.
* '''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 an "egg crate" shaped midsole. The insole can also make a difference to the cushioning. Cushioning is quite subjective, and it's the result of both thickness and firmness. There are also factors around how quickly a type of foam deforms, which can also change how a shoe feels. That makes it hard to put a single value on cushioning, but I've combined all these factors into a number for comparison purposes.
* '''Performance Penalty. '''Most studies show that for each 3.5oz/100g of shoe weight performance drops by 1%. However, there is also good evidence that cushioning can improve performance, so some allowance is made for the padding. I give figures for the slowdown based on 4 hour marathon pace, which is 9:09 min/mile or 5:41 min/Km pace.
* '''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. I rate shoes on a scale of 1 to 5, with a 3 as the average and 5 as longer longevity.
* '''Interference'''. Many shoes are designed to have features that are intended to interfere with the natural running stride. Shoes manufacturers try to use cushioning to reduce impact, medial posts to reduce [[Pronation]], and a raised heel (drop) to reduce Achilles' tendon stress. However, there is evidence from [[The Science of Running Shoes]] that this interference is both unwarranted, and ineffectual.
* '''Drop'''. Since the 1980s shoes have had a higher heel than the forefoot in an attempt to reduce the strain on the calf and Achilles' tendon, something that has shown to be ineffective. The extra height in the heel can encourage an excessive heel strike, and produces a shoe with relatively little forefoot cushioning. The extra height in the heel is called "drop", and shoes that have the same thickness at the heel and forefoot are referred to as "zero drop". While I believe a zero drop shoe is best, a drop of 4-5 mm is not overly intrusive. The amount of drop depends on how softly and thickly cushioned the shoe is. A thick, soft shoe will compress more and reduce the perceived drop. For example, the [[Hoka Clifton]] is softly cushioned and is 32mm/28mm, giving a 4mm drop. If the shoe compresses by 20% on landing, this will give 22.4mm/25.6mm for a ~3mm drop. I've included values for "loaded drop" that reflect the drop when the shoe is worn. Note that I measure drop from under the ball of the foot and under the heel, and different locations in the shoe can produce different values.
* '''Structure'''. The issues cushioning comes predominantly from the foam midsole, which can be a single density, or have multiple densities in an attempt to reduce pronation. The denser foam is also heavier, and the more extreme anti-pronation measures found in motion control shoes are correlated with higher levels of pain and injury. Therefore I believe that a shoe should have a single density of foam; simple is better.
* '''Flexibility'''. I believe that a shoe should be as flexible as possible, to allow a natural running style. However, high levels of cushioning create some intrinsic inflexibility, so this is another balancing act. Many shoes include grooves cut into the foam midsole in order to improve flexibility.
