Wednesday, 2 June 2010

Touch and Go #2

Posted by speedygeoff on Wednesday, June 02, 2010 with No comments
Katherine

Cushioning:
Impact forces are the other major scoundrel of running injuries. The thinking goes like this, the greater the impact force on the lower the leg, the greater stress the foot/leg takes, which could potentially lead to injuries. To combat this fear, running shoes, particular cushioning ones, are to the rescue. Let’s take a look.

The first question is, do cushioning shoes do their job?

Wegener(2008) tested out the Asics Gel-Nimbus and the Brooks Glycerin to see if they reduced plantar pressure. They found that the shoes did their job! But where it reduced pressure varied highly. Meaning that pressure reduction varied between forefoot/rearfoot/etc. This led to the interesting conclusion that there should be a shift in prescribing shoes to one based on where plantar pressure is highest for that individual person. It should be noted that this reduction in pressure was based on a comparison to another shoe, a tennis shoe. I’m not sure that this is a good control. Basically, this study tells us that cushioned running shoes decrease peak pressure when compared to a Tennis shoe.

In a review on the subject, Nigg (2000) found that both external and internal impact force peaks were not or barely influenced by the running shoes midsole. This means that the cushioning type does not change impact forces much, if at all. But how can this be? I mean it’s common sense if you jumped on concrete vs. jumped on a shoe foam like surface, the shoe surface is softer right? We’ll come back to this question in a minute.

Impact Forces: The picture gets cloudier:
But it’s not as simple as described above.

In an interesting study by Scott (1990) they looked at peak loads on the various sites of likely injury for runners (Achilles, knee, etc.). All peak loads occurred during mid-stance and push off. This led to an important finding that “the impact force at heel contact was estimated to have no effect on the peak force seen at the chronic injury sites,” and led to speculation that impact force did not relate injury development.

Further complicating the impact force idea is that when looking at injury rates of those running on hard surfaces or soft surfaces, there appears to be no protective benefit of running on soft surfaces. Why is this? Because of something called pre-activation and muscle tuning which will be discussed below.

Supporting this data, other studies have shown that people who have a low peak impact have the same likelihood of getting injured as those with a high peak impact force (Nigg, 1997). If you want to complicate things even further, impact seems to be the driving force between increased bone density.

As a coach or trainer this should make sense. The bone responds to the stimulus by becoming more resistant to it, IF the stimulus is not too large and there is enough recovery.

from Science of Running by Steve Magness. To be continued...

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