Home > Uncategorized > Running stride: speed vs. injury-proofing

Running stride: speed vs. injury-proofing

October 1st, 2011

Another great post on Amby Burfoot’s Peak Performance blog explores an important wrinkle in the ongoing debates about optimal running form. We tend to think that “better” running form is better in all relevant respects: we’ll be faster and less likely to be injured. But that’s not necessarily the case. Amby takes a look at a study from a couple of years ago that analyzed the gait of an ultrarunner who ran from Paris to Beijing in 161 days, averaging 53 km per day. As Amby writes:

You would think that 161 days of a marathon-plus per day would turn you into a lean, mean running machine. But that doesn’t happen, at least not when it comes to running economy… His stride became shorter and “smoother,” the word used by the physiologists to describe his decrease in aerial time with each stride… He reduced his landing force and also his loading rate. But his oxygen efficiency, or running economy, decreased by six percent.

This illustrates one of the conundrums faced by those attempting to run with shorter strides. It may in fact reduce your injury rates. It won’t necessarily make you faster.

The adaptations that this runner’s body made over the course of this epic run make perfect sense: after all, his top priority was to survive each day without breaking down. But it’s a good reminder that, when we talk about “improving” running form, we have to think carefully about what, exactly, we’re hoping to improve.

  1. Alex
    October 1st, 2011 at 02:14 | #1

    I think this is a bit of a straw-man. 161 straight days of that kind of distance would almost invariably result in significant muscle loss, and thus decreased running economy. I don’t think stride length is nearly as much of a factor as that.

  2. October 1st, 2011 at 02:48 | #2

    Are they using the word ‘smoother’ as a euphemism for shuffling? The abstract says “At POST, there was a tendency toward a ‘smoother’ running pattern, as shown by (a) a higher stride frequency and duty factor, and a reduced aerial time without a change in contact time…”. If his contact time remained the same, then I’m not very surprised that his running economy decreased. An important reason for adopting a shorter stride is to help decrease contact time. This is not a study that should be used for drawing any hard conclusions about running technique.

  3. Richard Ayotte
    October 1st, 2011 at 16:33 | #3

    Yes but…

    “Fuchs lost five pounds during the run, and his percent body fat dropped from 21.5% to 16.5%”

    the word used by the physiologists to describe his decrease in aerial time with each stride… He reduced his landing force and also his loading rate

    This tells me that he became a much more efficient runner and If he continued running at the same speed, he didn’t need as much oxygen and his body adapted, by making his oxygen uptake less efficient. If he however would have slowly increased his speed as he became more efficient, his oxygen efficiency, I presume, would have remained the same.

  4. Jules
    October 1st, 2011 at 17:45 | #4

    “You would think that 161 days of a marathon-plus per day would turn you into a lean, mean running machine. ”

    Umm, no. Quite the opposite actually.

  5. alex
    October 2nd, 2011 at 01:33 | #5

    @Richard: “This tells me that he became a much more efficient runner and If he continued running at the same speed, he didn’t need as much oxygen and his body adapted, by making his oxygen uptake less efficient.”

    I’m not sure I follow this line of argument. If his stride adapted in a way to make him a more efficient runner, why wouldn’t he burn less oxygen at the same pace? I don’t see why his body would “compensate” by automatically burning more oxygen.

    More generally: of course this is a somewhat extreme example. My intention wasn’t to suggest that all attempts to change running form are the equivalent of running 53 km per day for 161 days. It’s simply a reminder of what should be a very obvious and uncontroversial point: that running economy (and thus, ultimately, racing speed) and injury avoidance are two different things. I assume that it’s possible to make changes that improve both parameters, but if you improve one, it’s not a given that you improve the other.

  6. HK
    October 2nd, 2011 at 04:50 | #6

    Maybe his running economy decreased just because tired muscles are less efficient than fresh muscles. The mechanical efficiency of running (in other words, the form) makes only a minor part of total running economy and the biochemical processes at the muscular level are at least equally important. The amount of ATP synthesized from a specific volume of oxygen is not an universal constant, far from that.

    He might still have improved his mechanical efficiency, even if the total efficiency decreased because of tired muscle cells wasting a lot more oxygen than in the beginning. We don’t know that from this experiment.

  7. alex
    October 2nd, 2011 at 16:06 | #7

    @HK
    “We don’t know that from this experiment.”

    You’re absolutely right: this experiment proves nothing one way or the other. It’s main value (to me) is as a reminder that two things that we often lump together (efficiency and impact forces) are actually distinct elements that can change independently of one other.

    Let me turn the question around: is anyone here actually arguing that if I reduce my impact transients (or some comparable marker of “smoothness”) by 10%, my running economy should improve proportionately?

  8. Brian
    October 3rd, 2011 at 15:03 | #8

    I would question the effect of recovery (or lack of in this case) on his running economy. Running that distance for so many consecutive days will produce lingering metabolites in the body that could potentially make him less efficient. Plus, the amount of muscle damage incurred after each run means that fibers will not be working optimally the next day.
    This study is too extreme to make any real correlations on running economy.
    Reducing impact time should improve economy. I relate this to cycling efficiency where reducing the amount of time spent on the down stroke (muscle contraction) allows an increase of time for nutrient exchange at the capillaries during relaxation. http://www.ncbi.nlm.nih.gov/pubmed/20840561 The same should hold true for running. I suppose the relationship would be proportionate up to a point and then taper off. Thus, too short of a time on the ground will start making you more inefficient.

  9. Richard Ayotte
    October 3rd, 2011 at 15:31 | #9

    @alex
    My comment was fuzzy so let me try again.

    By the end of the journey, Fuchs’ biomechanics had became so efficient that his VO2 efficiency regressed. This regression and adaptation was caused by the lower oxygen requirements. Fuchs could have avoided the VO2 regression by increasing his pace as his biomechanics became more efficient.

  10. alex
    October 3rd, 2011 at 15:53 | #10

    @Richard: I think there may be some confusion here about the definition of “running economy.” The six percent decrease in economy INCLUDES any improvement in biomechanical efficiency. That means you’re effectively arguing that (1) he improved his economy through biomechanical factors by X percent; then (2) his body responded by making his economy worse (how?) by (X+6) percent.

    @Brian: “This study is too extreme to make any real correlations on running economy.” Agreed, and no one is trying to make any real correlations. The point is just to illustrate that running economy and injury resistance are two different entities.

  11. Richard Ayotte
    October 3rd, 2011 at 23:18 | #11

    @alex I just reread the abstract and you’re right, it’s 6.2% increased in cost of running, not 6.2% cost increase in VO2. Have you read the study? I’m curious in the details now. I’d like to know how VO2, VO2MAX, heart rate etc were adapted.

  12. RH
    October 5th, 2011 at 07:36 | #12

    Interesting. I have just read about the Verheul and Souplesse training methods, which advocate intervals instead of the long extensive runs of some other training philosophies. They argue that long extensive runs will make you an excellent slow runner of longer than-race distances instead of a fast runner of your race distance and that if you train intervals with optimum technique slightly slower than race pace, aerobic base and racing speed will follow from racing regularly.

    This does provide some sort of confirmation(OK, N=1, but still…) of the negative part of the theory, namely that making huge mileage in easy paced runs will ruin the economy, elasticity and reactivity of your stride. I assume that the last two entities are -apart from aesthetic descriptions- roughly the same as ground contact time vs aerial time and potential and kinetic energy change per step.

Comments are closed.