Pool running: oxygen use and max HR change as you get better at it
Pool running is very different from running on land. Aside from the crushing boredom, there’s also the fact that your heart rate stays lower for a given effort, and your VO2max is lower. This has been demonstrated in lots of studies, and is typically attributed to:
(1) an increase in central blood volume, as a result of the hydrostatic pressure causing a higher stroke volume and therefore lower heart rate for a similar cardiac output; (2) the thermal effect of water, since water temperatures below thermoneutral (33–35 C) reduce heart rate and increase stroke volume; (3) less muscle activity during deep water running because of the possible reduction of muscle activity of the weight-bearing muscles.
But even though most people agree about that, pool-running studies have produced conflicting results about exactly how much lower VO2max gets, what happens to your ventilatory threshold, how perceived exertion changes, and so on. According to a new study in the Journal of Sports Sciences (from which the above quote is taken), this may be because there’s a steep learning curve associated with pool running.
The study, by researchers in the U.K., South Africa and Brazil, compared 10 runners who had at least two months of pool-running training with a certified instructor with seven runners without pool-running experience. They had both groups perform VO2max tests and run at threshold, both on land and in the water. (The testing in the water was as problematic as you might guess, and the machines apparently broke down three times and data from four subjects had to be discarded.)
Going from land to water, the novices dropped the max heart rate from 186 to 172 and their VO2max from 55.1 to 44.3. In comparison, the experts went from 186 to 177 and from 53.8 to 48.3. In other words, they were able to work harder once they’d mastered pool running — probably, the authors speculate, because they’d learned to recruit more muscles.
Practical applications? Well, if you’re trying pool running for the first time, expect it to feel really hard and yet strangely unsatisfying as a workout. But be reassured that if you stick with it, you’ll be getting a better and better workout for the same effort.