Wednesday, October 10, 2012

Size matters

Ever since watching Floyd Lavery race sockless, I've always wondered how much the weight of socks matter to race performance. Haven't you? Today I read an article on the NYT blog (it's an old article) on the energetics of shod v. barefoot running and I didn't really care about the point of the article (barefoot is more expensive because we use active muscle to dampen contact forces which shoes do in shod running) but I zeroed in on the statement that an additional 100g of shoe adds about 1% VdotO2 to run at same speed. To determine how weight affects race performance I used an online running calculator that gave me the estimated VdotO2 for a given race performance. Here is what I found


10K time    VdotO2   %larger than VdotO2 @ 37 min 10K
37:00.0     52.26
36:55.0     52.4     0.27
36:50.0     52.55    0.55
36:45.0     52.69    0.82
36:40.0     52.84    1.11
36:35.0     52.99    1.40
36:30.0     53.14    1.68
36.25.0     53.29    1.97


I don't know if that's 100g in total shoe or per shoe. Let's say its total shoe. This means the difference in wearing say Asics Piranhas (122g) v. Saucony Kinvara (224g) is about 200g or 2% VdotO2 or about 35s over 10K assuming all else equal of course (like how much muscle work is being used to dampen impact forces). Thats about 1s/mile/oz/shoe. If its 1% per 100g per shoe then the difference would be only 17s. That's significant enough to me to wear Asics Piranhas (I do) or the Inov8 155s (I do that to). This doesn't mean I would advise you to wear Asics Piranhas or Inov8 155s  for a marathon because I'm guessing there would be variables other than weight (and having to do with dampening of impact forces) that would affect performance.

OK what about socks. Its hard to find the weight of socks but a pair of swiftwick aspire zeros weighs 23g for the pair. That's about an expected 0.23% difference in performance, or something just less than 5s according to the chart above. That's not very much and probably not worth the consideration. But then maybe you wear a heavier sock?

What about a pair of "performance enhancing compression socks"? I can't find how much these weigh. Plus the penalty in VdotO2 won't be exactly correct because lots of that weight is closer to the center of rotation. And then I'm not sure about the "everything else equal" assumption with compression socks since they are at least advertised to enhance performance because of the compression.

PS - well I just googled around and found the source. Confirms what I've written and fills in some unknowns as well.

4 comments:

  1. Jeff what about when trail running and tromping through water......the sox could hold a substantial amount at least for a few miles. It made me think of Stone Cat last year were we had to run though a stream about 400 feet long so the feet became very saturated and I could feel the weight difference. I suspect, without sox the water would have drained out much sooner.

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  2. Dr. Lieberman was discussing this when I was at his lab for the first time. There is probably a measurable difference, but I doubt the outcome would be that significant given the thousand of other variables which can effect your performance on race day.

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  3. good point about wet socks - twice the weight!

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  4. Hey Jeff I've also thought a bunch about this and to echo Kevin about "wet" and mud weight as well. I've definitely focused on shoes that evacuate water, and socks that don't hold on to too much when the get soaked. I feel it's made a difference, at least in the summer months. Thanks for all the info!

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