The Planet Wave: The Heat Is On, but It May Help

May 24, 2013 Posted By: Bob "Wish" Wischnia

Summer is nearly here which means lots of different things for different people, but for folks who are planning to run a fall marathon or half, it also means plenty of hot, humid long runs. Undeniably, one of the least appealing aspects to running a fall marathon is training through the summer for it. Depending on which part of the country you live, running the race is easier than slogging out 20-milers in July and August. Suffice it to say, summer is not exactly the ideal time of year to train for a marathon.

But if you’re at all like me and planning to run one of the big-city marathons such as New York City, Chicago, Philadelphia, Hartford, Twin Cities, Marines Corps, Portland, San Antonio, Richmond or Baltimore this fall, you’re probably already dreading the very idea of doing long runs during the dog days of summer.

Most marathoners know they can safely acclimate to running and racing in warm weather. Certainly, running in warm weather isn’t easy, but training through the summer toughens us and is great prep for whatever Mother Nature might throw at us in our fall marathons. That’s a given. But just imagine for one moment if training in the heat and humidity actually gave you a boost in the fall.

Imagine no more.

Simply put, training through warm summer conditions that are common in most of the Lower 48 actually has some of the aerobic advantages that training at altitude does. Seriously.

A brief review. Training for several weeks at an altitude above 7500-8000 feet increases red blood cell production and erythropoietin (EPO) which carries oxygen to the muscles. The more you have of this (up to a point), the more oxygen gets delivered to the muscles which is a huge advantage in sea-level races. That’s why most world-class runners head for the mountains.

Needless to say, most of us can’t put our lives on hold and move to Colorado Springs, but here’s the shocker: Marathon training in hot, humid summer conditions stimulates the body in similar ways that altitude does. This means hot weather training will improve your aerobic performance, not only in a warm race, but in a cool-weather race as well.

A three-year-old study by the University of Oregon’s Department of Human Physiology looked at the impact of heat acclimation and whether it could improve the ability to exercise in a cool environment. And, lo and behold, it did.

The UO researchers took 20 trained cyclists and split them up into two groups. One went through a 10-day heat acclimation process which included 10 sessions in a lab heated up to 104 degrees. The cyclists rode easily for 45 minutes, rested 10 and then rode another 45 minutes at a leisurely pace. The other cyclists did the exact same training, but in a cool lab (about 55 degrees) so they didn’t acclimate to heat.

After that, the cyclists performed time trials in controlled conditions that were both hot and cool. To make things even harder, before the time trial, the cyclists were immersed in warm water to elevate their body temps so they started off running hot. (Hope these cyclists were well-paid for this torture.)

What the researchers found was that the 10-day heat acclimation process the “heat” cyclists were put through, resulted in a five percent increase in VO2 max during cool conditions and an eight percent boost in hot conditions. (VO2 max is the max capacity of the body’s ability to transport and process oxygen during exercise. Important stuff.) Equally good, the heat acclimation also increased the power output by five percent in the cool temps as well as the hot.

“The results were quite dramatic,” said Dr. Santiago Lorenzo, the UO lead researcher who is now on the faculty of Lake Erie College of Osteopathic Medicine and who incidentally finished 24th in the 2004 Olympic decathlon. “The heat acclimation was to be expected, but the magnitude and consistency of the boost that the heat-trained group received was surprising.”

While it’s hardly surprising that the heat-trained cyclists performed better in the heat than the control group of cyclists, that was only part of it.

In the all-important category of plasma volume, our heat-trained friends increased their volume by a whopping 6 ½ percent, while the control group showed no changes. This is particularly significant for us because when we run, our plasma volume—the volume of plasma in the blood vessels—goes down by as much as 20 percent. The more we sweat, the more the plasma drops because the body is working so hard to cool itself. As the plasma volume continues to plunge on a long, hot run, there is a corresponding rise in the concentration of red blood cells.

We all know how difficult it is to run hard and long in the heat. The reason it’s harder (than say on a dry 50-degree morning) is once we heat up, the blood flow to the working muscles gets messed up and when it does, the heart has to work a lot harder to pump blood around the body to cool off. Another words, it’s a lot of work and puts a strain on the body.

No surprise there. But the Oregon study shows that once we’ve adapted sufficiently to the heat (and believe me, if you’re training through the summer, you will quickly adapt), our plasma volume is significantly increased which means we have more blood to work with as the heart adapts to the increased work it takes to cool the body’s core temp. For sure, any type of training in any weather, will increase plasma volume, but heat training increases it even more—similar to training at altitude.

While the Oregon study dealt only with cyclists, it’s probable that the findings are equally applicable to marathoners and other aerobic athletes. Says Dr. Chris Minson, the senior author of the Oregon study, “We saw significant cardiovascular adaptations which might confer benefits to athletes, no matter what the temperature in which they’re training or racing. Even though we looked at cyclists in a very tightly controlled environment, my best guess is that the findings would apply equally to runners and other endurance athletes.”

The bottom line in all this is if you survive marathon training this summer it will have a positive aerobic impact when you finally make it to the starting line of your fall marathon—even if the temps are cool. This isn’t any guarantee that you’ll PR (darn it), but heat-trained marathoners are aerobically fitter than runners of the same ability who may have trained in cooler, dryer conditions.

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