Spit Or Swallow? Science Weighs In.
Finally got a chance to sit down and read some more interesting research in the ACSM Medicine & Science in Sports & Exercise March issue. The first article that struck my interest was out of the United Kingdom called “The Influence of Ingesting versus Mouth Rinsing a Carbohydrate Solution during a 1-h Run.” In the study, the effect of ingesting a carbohydrate solution on the distance ran in 1 hour by “recreational runners” was compared to mouth rinsing.
Per the researchers, recreational runners were characterized as having a VO2 peak of 65.0 + 4.4ml-kg. I think that definition makes me a powerwalker. Another cool tidbit is that the tests were run on a Runner MT2000 treadmill that has an “ultrasonic feedback-controlled radar modulator that spontaneously regulates treadmill belt velocity corresponding to the changing position of the runner on the treadmill belt.” Shoot, I cant get my treadmill to stop even when I’m being dragged on the belt by my face.
Anyhow, the study found that rinsing and then ingesting a carb solution significantly improved 1 hour running performance in comparison with mouth rinsing alone and ingesting a placebo solution. This is consistent with prior research, even those run in “real life.” For example, an earlier study showed that ingesting a 6% or 8% carb solution during a 15km road race increased running speed by 5% during the final 1.6km compared to water.
These results are in contrast to a 2008 study by Pottier et al that showed rinsing with a carb solution improved cycling performance versus ingestion. Per that study, researches hypothesized that rinsing with a carb solution improved performance by acting through a central nervous system process. Of course, as the current study is quick to point out, you cant really swallow without sort of rinsing your mouth first. Researchers from the 2008 study got past this by saying that the transit time (mouth to throat) was fast enough to not really have an effect.
To account for this discrepancy, participants in the current study were asked to hold the solutions in their mouths for 5 seconds before either spitting or ingesting. Thus, what this study really found was that “combining mouth rinsing and ingesting a carbohydrate-electrolyte solution was 85% and 95% likely to benefit a 1-h run performance.”
Now, this is great on paper, but the authors are quick to point out some limitations. First, even though they noted improved performance with the rinse and swallow group, they did not detect any differences in HR, body temperature, or blood lactate. It also depends on what your carbohydrate status is prior to running. For example, for those who ate 3 hours before running, no improvement was found with carb fluid ingestion during exercise. All the participants in the current study fasted prior to running. In addition, there isn’t a clear metabolic reason why carb ingestion during short intensity (<1h) exercise should matter. Studies have shown that endogenous glycogen stores are much more important for such events. The main hypothesis at this time is that car ingestion activates parts of the brain that in turn results in improved utilization of endogenous glycogen.
All in all, while supportive, the authors say its too early to recommend that everyone rinse and swallow; more research is needed. So in the meantime, I’ll keep my fluid carb intake the same – through a post race keg stand.