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For the triathletes out there, an interesting study has been posted online for publication in a future issue of the European Journal of Applied Physiology: “Combine cycle and run performance is maximized when the cycle is completed at the highest sustainable intensity.”
A pair of Australian researchers asked a group of triathletes to perform a series of four 20K bike/5K run time trials, with the intensity of the bike ride varying from 80% to 100% of max intensity (compared to an isolated bike trial they’d done previously). As expected, going harder on the bike led to slower times for the run — but the effect was most pronounced for just the first kilometre of the run, after which it didn’t really matter how hard the subjects had gone on the bike. As a result, the fastest overall bike-run times came when the effort on the bike was highest. In other words, holding back in any way on the bike loses you time that you can’t make up on the run.
Now, there are a number of caveats. The study was small (5 men, 3 women), but the effect was very clear-cut (average times of 62:40, 59:53, 58:29 and 56:37 for the four trials, going from easiest to hardest for the bike leg), so that’s not likely to be an issue. The fact that the distances were 20K-5K instead of 40K-10K is unfortunate. The authors do a song and dance about how the sprint distance is “growing in popularity” so that’s why they decided to study it, which seems absurd. I assume the real reason is that it would have been much harder to get volunteers to do that many 40K-10K efforts in succession. Also, it was a lab study done on stationary bikes with no wind resistance, and the triathletes were recreational — their average 5K time (not preceded by a bike ride) was 19:51.
Still, bearing all these things in mind, it’s a data point:
It is unclear if this relationship would hold for longer-style triathlon race formats, full triathlon races which also include a prior swim leg, races that involve a draft-legal cycle leg or with highly trained or elite triathletes. However, our results suggest that time lost on the cycle leg is unlikely to be made up on the run leg.