"The more you eat, the faster you go.. in ultraendurance"

[Jwolf]

Interesting blog post from Alex Hutchinson, with references to some primary research articles:

http://sweatscience.com/the-more-you-ea ... endurance/

A few months ago, I blogged about a study that observed correlation between in-race carb intake and race time in Ironman triathletes. What was significant about that paper is that it looked at a topic that has been studied to death in the lab, and took it out into the real world. There are a lot of “problems” with the real world that make it hard to nail down causes and effects — but ultimately, the whole point of this type of research is to understand what’s happening in the real world. So these observational studies, despite their challenges, are very important.

That’s by way of intro for another small study, just published in the International Journal of Sport Nutrition and Exercise Metabolism, from researchers in New Zealand. They looked at the nutritional intake of participants in a brutal cycling race, the K4, which covers 384K and includes 4,600 metres of climbing. The average finishing time of the 18 study participants was 16 hours and 21 minutes! The key points:

The estimated calorie burn for the race was about 6,000 calories; the average intake was just 4,500 calories, so there was a big caloric deficit.
There was a significant inverse relationship (p=0.023) between number of calories consumed and finishing time. The more calories you managed to cram down your gullet, the faster you finished!

Is this a surprise? Given that the race was so long, it makes sense that taking in enough energy was a significant challenge. Obviously the same thing doesn’t apply during, say, a 100-metre sprint. The question is: where’s the breakpoint, beyond which energy intake becomes a significant independent predictor of performance? I think the general assumption is that it’s probably a bit below marathon distance — so it would be really interesting to see a study like this, with a very large number of participants, at a marathon.

The last paragraph is of particular interest to me. I agree that it would be interesting to see a study like this performed on a large group of marathoners. I suspect that the results would not necessarily be completely predictive-- that some marathoners might benefit from more energy consumption, others less so.

[turd ferguson]

"There are a lot of “problems” with the real world that make it hard to nail down causes and effects"

The side of the road is littered with the remains of scientists who can't figure out why what looked so simple on the blackboard didn't work in the real world, many of whom insist that they're still correct and that the real world is wrong.

[drghfx]

I'd be interested to see the average speed per k of the cyclists in the race and a per k breakdown. If the guys who took in the most calories kept up their starting pace or even got faster while the other guys couldn't maintain their starting pace then I'd say the study has some merit. However, if everyone was able to maintain their starting pace for the whole race, then you might be able to hypothesize that the guys who took in the most calories were just faster. I know, there are a lot of other potential variables as well.

[phorunner]

I think the real question is it "they're faster because they consumed more calories", or is it "they consumed more calories because they're just faster and need more energy"?

It's tough to compare people against themselves - changes in training over time probably have a bigger effect - so it must be even harder to compare performance across the field.

[La]

I think the real question is it "they're faster because they consumed more calories", or is it "they consumed more calories because they're just faster and need more energy"?

Or even, "Do people who are naturally faster NEED more calories to perform at that level than those of us who are not as fast?"

What impact does calorie consumption have on an individual's performance (against himself) as opposed to his performance against someone else.