Why Fast Starts Slow You Down

Running, as a great article about U.S. Olympian Ian Dobson a few years ago put it, should be mathematical—but it’s not. In theory, if you know someone’s VO2max, lactate threshold, and running economy, you should be able to calculate how fast they’ll be able to run. In reality, as the recent debate about the prospects for a sub-two-hour marathon has revealed, it doesn’t work that way.

One of the sources of additional complexity is that quantities like running economy (i.e., how much oxygen, and therefore how much energy, someone requires to cover a given distance) aren’t fixed in stone. If you measure someone’s running economy in the lab, that’s what it will be at the start of a marathon. But will economy be unchanged after an hour of running? Two hours of running? Growing evidence suggests it won’t.

A new paper in the Journal of Strength and Conditioning Research, from researchers at the Norwegian University of Science and Technology, takes an interesting approach to this question. The study involved seven world-class orienteers and skiers, with an exceptionally impressive average VO2max: 80.7 ml/kg/min.

The gist of the study was: Have the subjects run hard for a while to tire them out; then allow them to recover for a few minutes until their lactate levels reach either 3 mmol/L or 5 mmol/L; then measure their running economy while running around threshold pace.

The key result was that when they were less recovered (i.e., 5 mmol/L of lactate), their running economy was 5.5 percent worse. That’s an enormous difference. The authors estimate that it corresponds to a difference of 30 seconds in a 10-minute run, three minutes in a one-hour run, or 8.25 minutes in a 2:30 marathon.

This doesn’t, I should emphasize, mean that lactate causes changes in running economy. Lactate is a convenient and easy-to-measure marker of fatigue and metabolite accumulation; its rise and fall corresponds with other metabolic changes in muscle like accumulation of potassium, phosphate, and reactive oxygen species. It’s not at all clear which, if any, of these factors contributes to the change in running economy.

From a practical perspective, the authors suggest that the results are a good argument against starting too fast in a race. If your fast start causes an accumulation of lactate (and all the associated changes), you’ll be significantly less efficient for the rest of the race.

It’s worth noting that there’s a body of literature suggesting that, for shorter races, a fast start might actually be helpful—precisely because it helps ramp up oxygen consumption quickly. If you’re racing for two minutes, it’s all about how quickly you can deliver energy; if you’re racing for two hours, on the other hand, efficiency is king.

Subscribe to Runner's World

Related Articles