Tuesday, March 3, 2009

Caffeine's Effects on Endurance and Sprinting in Rowing

Caffeine is one of the most widely used drugs and has been shown in many studies to enhance athletic performance--especially for endurance athletes (for example here (pdf), here and here; this one is specifically about rowing performance).
In 2004, the World Anti-Doping Agency and US Anti-Doping Agency removed caffeine from the list of banned substances (see here for rowing). Given how well-known the performance enhancing effects of caffeine are, it's very likely that many high-level athletes take caffeine prior to competing.
In order to find out what the effects of caffeine are on my own endurance performance, I performed an experiment in which I did 32 tests on the Concept 2 rowing machine over the course of 8 months. For half of the tests I took caffeine pills one hour before starting and for the other half I took a placebo (vitamin C pills). I drew the pills randomly and blinded myself to which pills I was taking so that at no point during the experiment did I know what pills I had taken for any test. I did the tests with roughly one week between each one, during which time I exercised moderately for about an hour a day. The dose of caffeine was two 200 mg pills (400 mg), which is roughly equivalent to 4-6 cups of coffee (a smaller dose than is often used in experimental studies and one that would have been unlikely to produce a violation when caffeine was a banned substance).
Each test had two parts. First, with no warm-up, I did one hour on the rowing machine at maximum effort at 20 strokes per minute. Second, five minutes after the end of the hour, I did a 300m (roughly 48 second) sprint at open stroke rate (the rating was usually 45-48 strokes per minute), again at maximum effort.
[Aside for those unfamiliar with the Concept 2 rowing machine: just like a treadmill or exercise bike, the rowing machine measures power output as you simulate the motion of an exercise. Two common measures of power output that rowers use are watts and speed. Speed is often quoted in terms of split times per 500m or total meters for a given time. I use both measures of speed, as well as watts, below. The rowing machine also tells you how many strokes you take per minute (the "rating"), which I kept constant during the 60 minute tests. Finally, unlike a treadmill, and more like an exercise bike, the rowing machine does not limit your speed. You can go as hard or as easy as you want at any time, with the machine's resistance increasing as you increase your effort. As someone who is also a competitive runner, I can say that a 60 minute test on the rowing machine is qualitatively very similar to a 60 minute time trial running on the road.]
The results of the tests, charted over time, are shown below in meters for the hour test and in watts for the 300m test. Black symbols represent the caffeine tests and red symbols represent the placebo (non-caffeine) tests.

The caffeine had a very strong effect on my performance on the one hour test. On average, I went 177 meters further in an hour when I had caffeine (equal to 1.1 split seconds/500m or 9 average watts) than when I had the placebo. This is roughly a 3% difference in average watts between the caffeinated and non-caffeinated tests. The graph shows that this effect was fairly consistent, even when my overall power varied over the months of the experiment The average of my caffeinated 60 minute tests was better than my best non-caffeinated 60 minute test. In fact, my best non-caffeinated 60 minute test was slower than my 11th-best caffeinated test.
The caffeine had a relatively smaller effect on the 300m sprint. My average power was about 1.7% percent higher for the caffeinated sprints than the non-caffeinated ones. As the graph shows, the effect of caffeine on the 300m test is harder to distinguish from random variation. I don't know whether the caffeine would have a different effect on a sprint done without the hour test beforehand.

The results I found for the one hour test are similar in magnitude of effect on split times to the results of the study of caffeine use on rowing performance referenced above. In that test they find that taking caffeine before a 2000m test leads to roughly a 1% improvement in speed, which means about 1 split second/500m.
Two major limitations of my study are that the results are only for one person and that the tests I chose are not the standard 2k or 6k tests that are most relevant to competitive rowers. Both limitations are partially addressed by the other study of caffeine on rowing performance that I cite above. Also, if my schedule permits, I intend to do a similar study for 6k tests on the rowing machine this fall. My main limitation is in finding the time and motivation to do enough tests to get a meaningful result. Doing 32 one hour tests over the course of eight months was mentally difficult. For that reason, if I do the 6k study, it will have many fewer data points. I will leave studies of the 2k test to other experimenters.
My perception is that the use of caffeine among American rowers is not pervasive--even among those who compete internationally. I find this surprising given that it is well within the rules and that other countries' athletes may take every advantage possible (see short discussions of this here, here and here). Even when caffeine was "banned," the allowable limit was much higher than the level seen to produce performance effects. I'm especially surprised that I know of no coaches who address whether athletes should use caffeine during selection or during competition.
The issue is similar with pseudoephedrine, another drug that was taken off the banned list in 2004. It is less clear whether pseudoephedrine is useful as a performance aid, though (for example see here, here, here and here).

A few notes:
I am a retired competitive sculler. I retired from competition about three weeks before beginning this study in July 2008. I did most of my competing at the national level, with a few appearances in international competitions, including the World Championships. I am 6'3" tall and during this experiment my weight was consistently close to 90 kg or 200 lbs.
During the experiment, I was often (but not always) able to feel whether I had taken caffeine or not, even though I wouldn't actually get confirmation until the whole experiment ended. I noticed no tendency for the caffeine to dehydrate me, but it did seem to interfere with my sleep sometimes.
The caffeine pills and vitamin C pills were the same size, shape and texture. They did have a different taste, however. In order to keep this from affecting the results I would put the pills under my tongue and swallow them quickly with a glass of water. This worked quite well to keep me from tasting them.
For the 60 minute test I didn't sprint at the end. Instead, whatever speed I was holding with around eight to 10 minutes left, I would maintain until the end. This allowed the 300m test to be the real measure of whether caffeine affects sprinting ability.
One of the studies I cite above finds that the effect of caffeine is smaller in those who use it frequently. I rarely have caffeine, so my results probably better represent what a non-caffeine user could expect. Also some studies have found that getting caffeine via coffee is unreliable and may not produce the same performance effects. For that reason, I recommend caffeine pills to those who want to test the effect on their own performance.

For those who are interested, using a standard t-test, the p-value for the hypothesis that the caffeine had no effect on the 60 minute test is less than 0.1%, and for the 300m test is 5.9%.

1 comment:

  1. Hi,

    I read the article in New York Times about caffein and running the day before the first race of this spring. I decided to drink an espresso before the race and that gave me a boost, unfortunaly a little to much so I took off in a way to quick pace and was stucken by lactid acid.

    Read about it here:

    But I will still use some coffea when I feel the need for a little extra boost. (But I guess the placebo effect for me might be even greater than the real effect).