I’m spending a significant chunk of my Thanksgiving break in Seattle, for the purpose of running what will be my second marathon this weekend. Running, like cooking, is helping to keep me sane in the midst of teaching labs, finishing my dissertation research, writing said research up for publication, and trying to sort out what happens after my committee decides I’ve earned a handful of extra letters after my name.
My first marathon was last year’s Portland Marathon. Prior to 2009, I’d never run a race longer than five miles, but then that spring I let friends talk me into a half-marathon, and after running more than 13 miles, 26.2 suddenly didn’t seem quite so insane. Even so, training up for Portland was more than enough to make me realize that running what was (for me) a 3 hour-45 minute course is not really the same thing as running eight or nine 5k’s in a row.
I can make it through even a half-marathon on a good breakfast and carefully-judged pre-race hydration, but to go much longer I need more food (and water) mid-run. The long-term exercise involved in a long race is fueled by a combination of fat reserves and glycogen stored in the liver and muscle tissue. Glycogen is the more efficient fuel, so as exercise intensity increases, muscles draw on it more heavily.
If his muscles runs out of glycogen, a runner “hits the wall,” and may be forced to stop running altogether. I’ve done this a few times on long training runs, and it’s not pleasant—I’d end up all but walking the last couple painful miles. How long I can go before I hit the wall depends on my glycogen reserves, which in turn depend on the muscle mass in my legs—but it also depends on how fast I’m running, since glycogen use increases with effort. A computational study of the interactions between exercise intensity and glycogen consumption suggests that my first marathon time, 3:45, was close to the upper limit of glycogen consumption for a “trained endurance athlete”—and I probably don’t really qualify as “trained,” in the sense the study uses. So to survive a marathon, I have to take on supplementary energy mid-race, for which I will carry tubes of disgusting sugar syrup.
Shoes matter. Who knew?
Before I started training for Portland, I didn’t pay much attention to the state of my running shoes—I bought new ones when the holes in the uppers got too obvious. That’s okay when the longest run I do is about eight miles—once my weekly schedule started including longer distances, I noticed more post-run pain when my shoes’ insoles deteriorated. I began investing in gel insole inserts and actually paying attention to how much mileage my shoes had accumulated.
The funny thing about shoes, though, is that familiarity is almost as important as adequate support. Last year I bought new shoes about a month out from the marathon—and ran some truly miserable long runs in them. Lesson learned. It turns out that a new pair of shoes takes some breaking in, especially if you switch brands, as I had. I ended up running the marathon in the shoes I’d considered shot (with new insole inserts), and felt better at the end that I had on a fifteen-mile run in the new ones. I now stick to one brand of shoes, with the same inserts if possible, and I don’t wear new shoes on a long run until I’ve worn them on a number of short ones.
Part of the reason that my running comfort is so sensitive to the quality of my shoes may be that human feet aren’t evolved to run in running shoes. Running on two legs sets humans apart from our closest evolutionary relatives, and we’ve probably been doing it for millions of years—but highly padded running shoes are a very recent invention. This is the central argument in favor of a recent fad for barefoot running [PDF]—that, once you build up some necessary calluses, running without the artificial support and padding of a running shoe is less stressful. A biomechanical comparison of barefoot and shod runners provided some of the first data to support this hypothesis earlier this year. Essentially, barefoot runners tend to land each step toes- or mid-foot-first [PDF], which absorbs the force of a foot-strike more effectively than the heel-first tread of shod runners.
I did see a few of my fellow marathon runners wearing nothing but “barefoot” running shoes like the ones pictured here, which provide protection against rough pavement but no artificial padding. I’m not going to be doing that any time soon. But maybe I’ll try to add some barefoot workouts into my training routine, if I survive Seattle and decide to run a third marathon.
I intend no endorsement of any products pictured or linked to in this post. Thanks to Conor O’Brien, who pointed me to the PLoS Computational Biology article cited above.
Jungers, W. (2010). Biomechanics: Barefoot running strikes back. Nature, 463 (7280), 433-4 DOI: 10.1038/463433a
Lieberman, D., Venkadesan, M., Werbel, W., Daoud, A., D’Andrea, S., Davis, I., Mang’Eni, R., & Pitsiladis, Y. (2010). Foot strike patterns and collision forces in habitually barefoot versus shod runners. Nature, 463 (7280), 531-5 DOI: 10.1038/nature08723
Rapoport, B. (2010). Metabolic factors limiting performance in marathon runners. PLoS Computational Biology, 6 (10) DOI: 10.1371/journal.pcbi.1000960