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Interesting article [LINK FIXED] on what intense biking does to your running form, by researchers at the Australian Institute of Sport and the University of Queensland, coming up in a future issue of the Journal of Science and Medicine in Sport. There has been quite a bit of prior research on what happens when you run off the bike, generally showing that your running economy is worse than it would otherwise be — in other words, tired as you are, you also have to burn more energy to run at a given pace than you normally do. Various reasons for this have been proposed: you’re dehydrated, your breathing muscles are tired, you’re burning a higher proportion of fat because your carbohydrate stores are depleted. But it may also have something to do with running form, thanks to changes in neuromuscular control. That’s what this study set out to investigate, by having a group of 17 moderately trained triathletes do a pair of runs with and without a 45-minute high-intensity bike ride beforehand.
Unfortunately, the results don’t reveal any universal truths about what triathletes do wrong off the bike — but there are some interesting findings. First of all, everybody was different: some people had changes in running form, others didn’t; some had better running economy, others had worse. Crunching the data, the researchers find that the people whose running economy got worse had some things in common. When running after biking, these people tended to extend their knee and dorsiflex their ankle at the moment of ground contact a bit more than when they ran fresh. That makes them more likely to have a jarring heel strike, which wastes a bit of energy. Basically, when they start running after biking, they’re overstriding.
I’m not sure this really says much about fancy concepts like “neuromuscular fatigue,” but it does offer a useful warning about a pitfall that about half the subjects in the study fell into. Yes, you’re tired when you come off the bike, but overstriding isn’t going to get you to the finish line any sooner. (And one thing the researchers note is that their subjects were not elite triathletes, so this advice may be most relevant to less-experienced age-groupers.)
Excellent post and interesting study. One factor to add is that recreational triathletes typically ride at the lower end of the cadence range on the bike. When they get off the bike, this can influence running cadence which is then slower as well. Slower running cadence sets the runner up for over-striding. One other major contributor to lack of economy after the ride, is poor posture on the run. The forward posture of bike position is hard for some to shake off at the start of the run.
Thanks for the comments and input, Geordie — good points. The literature review in the study talked about some of this — it mentioned that an earlier study did indeed find that a more forward-leaning posture is part of the explanation for reduced running economy off the bike. Cadence is more controversial, but as you say, it may depend on the experience level of the athletes tested.