My body protested the heat jump constantly as I was running, sweat dripping down my face during a sunny, 80F's run. Guess what happened the next day? Yeah, the same thing.
I love running midday because it breaks up my day nicely. Work, mental break, work some more. The temperature is usually at its hottest when I sneak out the door though.
It got me thinking though, am I stupid for heading out in the heat? Should I just go run in the morning or at night when it's cooler?
It turns out the exercising in the heat has benefits, potentially quite powerful ones. This assumes of course you don't pass out from heat exhaustion.
A study was done in 2010 using cyclists. The riders were divided into 2 groups.
One set began heat acclimation which involves riding in the heat over a period of days for the body to adjust. In the study, the riders completed 10 training sessions in a lab heated to 104 degrees.
The cycling effort was "easy" paced for 45 minutes, rested for 10 minutes, then rode for another 45 minutes during each session.
A second set of riders, acting as a control group, completed the same training but in a cooled laboratory, so that they would not become heat acclimated.
Afterward, each rider repeated the laboratory performance tests from earlier, to see how they now compared. The laboratory in which they rode during the cool sessions was chilled to 55F.
The cyclists who performed heat acclimatization were 4-8% better over the distance than those in the control group! This is a dramatic difference, especially at an elite level. I wonder if a 4 hour marathoner, who simply performed a portion of their training in the heat, would be able to perform 10 minutes faster from the training?
The riders in the study were all trained athletes (and cyclists, not runners), so it's not clear how exactly this transfers to an amateur, or even elite runner. We can extrapolate that there are benefits to heat training, and racing cool, much like there are benefits to training at altitude and racing at sea level.
That's not to say that altitude training is comparable to heat training, or you will reap the same benefits. Each appears to stress the system differently, but with the same underlying ideas. Your body is stressed and forced to respond by more efficiently transporting oxygen. That's to say nothing of the psychological benefits, which will be more variable among folks.
Running in the Heat: How do you get acclimated?
The short answer is, you spend time "running the heat" - up to 100 minutes per day of exercising in hot temperatures.
The longer answer is, well, much longer:
Human’s ability to sweat allows us to cool our bodies even when running in extremely hot environments. However, the need to circulate blood out to the skin periphery for this cooling draws this much needed blood away from working skeletal muscles and causes a lower cardiac filling and stroke volume leading to higher heart rates at any given work load. The loss of electrolytes and fluid via the sweating (without adequate replacement) will lead to a decreased blood volume and add additional demand on an already taxed heart. Heat acclimatization is one way to improve ones ability to run well in a hot environment and in extreme cases is necessary for survival. Heat acclimation is merely when an individual has been conditioned to maintain a higher blood plasma and volume level, increased sweat rate, a decreased salt amount in the sweat produced, decreased fatigue rate of sweat glands, and quicker onset of sweating when placed in the heat. These changes are all needed to meet the demands on the body mentioned above. Heat acclimation is produced via repeated exposure to heat sufficient to raise body core temperature. This is most effectively done by exercise (skeletal muscle contractions) vs. sitting in a hot room. Only a few sessions of one hour of moderate exercise in the heat will produce an effect in un-acclimated individuals with changes being seen in a few days. Some interesting highlights to acclimatization:
- One can become acclimatized to heat and cold at the same time. Even with training bouts being on the same day in the different environments.
- Most of the improvements in heart rate, core and skin temp, and sweat rate are acquired in just ONE week of heat exposure. Heart rate adaptations are seen in just 4-5 days! However increases in sweating and a feeling of “ease of walking” in a hot environment can take up to one month to occur.
- More is gained from a 100 minute bout of heat exposure exercise than one 50 minute bout, but adding bouts beyond 100 minutes of exposure did not quicken adaptation.
- Heat exposure adaptations have been studied to disappear as quickly as one week if the subject is not re-placed in the heat, but may last as long as 3 weeks in some individuals.
All facts taken from “Human performance physiology and environmental medicine at terrestrial extremes” Pandolf, Sawka, Gonzalez. ISBN: 1-884125-02-6
Don't be overzealous
Be sure to undertake the desired heat adaptations gradually, through easy sessions. Don’t rush or overdo the acclimation process. Heat injuries can have severe consequences. Never attempt to "tough it out".
Overheating can be dangerous (which is why heat acclimation exists, of course). If you begin to feel ill during any of the acclimation sessions, slow down or stop. It can also help to have water/sports drink with you during your run.
The moral of the story is don't shun running in the heat, you are actually benefiting from it. Embrace it, enjoy it, and don't be stupid.
Resources for learning more