Danny Komen wrote:
I'm not sure if this is from that Lieberman study but here's a video of an adolescent kenyan boy running without shoes. Was this what you were referring to Malmo?
http://www.youtube.com/watch?v=pgkWhcapWLU- Enjoy.
Obviously you haven't been following this thread. It is not what I was looking for. It doesn't have the force plate results that were on the videos supplied in the paper.
Back to the study. It seemed to be a bit suspicious that Lieberman would ignore the data that showed that forefoot strikers (at least in the one case he illustrated) had higher impact forces, than those of the heel strikers, then chose to focus on the 'impact transient' of the first 50 milliseconds. I thought that what's the difference between 50 ms and 100ms (the time that it takes to reach maximum impact values? SO what I did is averaged out the maximum impact values and divided that by the time it took for each foot to generate maximum impact forces. My thought here is that force divided by a time measure is, by definition, POWER, and since the only propulsive forces generated during running is the time that you foot is on the ground -- unless you believe in kindergarten physics that gravity provide forward movement.
Barefoot heelstriker
avg maximum force was 2.45 bw
avg time to max force was 92 milliseconds
force/100ms = 2.68bw
Shod heelstriker
avg maximum force was 2.465 bw
avg time to max force was 117 milliseconds
force/100ms = 2.10bw
Barefoot forefoot striker
avg maximum force was 2.58 bw
avg time to max force was 100 milliseconds
force/100ms = 2.58bw
Shod forefoot striker
information hidden by researchers.. Ahem...
What is interesting here is that while the forefoot striker was generating more force on the ground, he is generating less power than the heel striker. The heel striker is simply transferring energy to the ground faster, generating more power, and that efficiency might go a long way to explain why the two most prolific 1500m runners in history were heel strikers.
Of course, we have only three videos to draw data from, and who knows, maybe an analysis of the rest of the videos might reveal something different?
Of course the researcher in this case is looking at impact and 'impact transient' as bad things. The problem with this is that impact forces are what generates forward velocity, and that 1/10 of a second when the foot is in contact with the ground, is were all of the forward velocity comes from. In athletic competition that's what matters.