Hot! Hot! Hot!

Posted: July 22, 2011 in Lifestyle
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As you are no doubt already aware, I have become rather fixated on cracking this heat issue; specifically now that I have this heat wave to take advantage of.  So, here I am – like an idiot – out huffing and puffing and sweating my way through long workouts like a pregnant water buffalo in the 31° heat and 43% humidity.  And in doing such, I have received lots of emails from concerned family and friends lately questioning my sanity in continuing to train through this extreme weather.

No, mom, I haven’t completely ‘flipped my wig’.

But rest assured, folks, I’m not taking this type of training lightly.  But, simply put, if I don’t get acclimated to the heat now, what happens in September when it’s hotter and more humid than it is now?  Right.  Remember, I want to do well in my first International Ironman series race and not end up as an oily stain somewhere along the race course; and dead triathletes aren’t likely to medal in their age category, are they?

This post’s intent then, besides boosting my own confidence level, is to help others understand what I’m attempting to do through this process and, hopefully, provide them some sort of similar comfort level regarding my heat specific training.  So while this type of conditioning is still no picnic, per se, I am approaching it with an educated mind with safety first and foremost on my mind.

For the record, I do understand the basics:  fuel properly; wear light clothing that doesn’t restrict sweat evaporation; and hydrate, hydrate, hydrate – got it.  I also understand that in order to get better acclimated to the extreme heat and humidity I also have to condition myself to be able to withstand the extreme duress so I have been spending a great deal of time educating myself on the most effective way to safely train for a race in this type of hot environs.

When I first started in triathlon it was as simple as getting out there, sucking it up and getting’ er done.  But that was for the shorter Sprint-distance events and, let me tell you, conditioning changes significantly when you begin competing at the longer distances.  Suddenly there are new variables that simply didn’t register as vitally important before.  What I am learning now is that there are two important mechanisms for keeping your body temperature regulated (a physiological process known as ‘thermoregulation’):

  1. As your muscles crank out the heat, blood flowing through muscle tissue absorbs the heat and carries it away and toward the skin. Triggered by an uptick in core body temperature, your brain sends a signal to the blood vessels in your skin to dilate or expand. This allows the skin to hold a larger volume of warmed blood. If the ambient air is cooler than the temperature of your skin, a heat exchange occurs, and heat from the blood circulating in the skin is released to the cooler surroundings. You cool off in the process.
  2. Heat loss is further accelerated by sweating. As you exercise, your core temperature rises and your sweat glands receive a signal from the brain to begin secreting sweat onto your skin. If the ambient air is sufficiently dry, sweat evaporates from your skin and a cooling effect takes place.

However, when the air temperature exceeds 96.8°F (36°C), as it has been approaching the past few days, instead of heat flowing from your skin to the outside environment, heat exchange is reversed and your body begins to absorb heat from the environment. So when it’s scorching outside, one of your two key thermoregulatory mechanisms has essentially been knocked out of commission.  Definitely not Winning.

When this occurs, sweating becomes the primary means for eliminating the heat generated by muscle contraction. When you’re training or competing hard outdoors in the heat, a sweat rate of 34–85 fl oz per hour (1.0-2.5 liters per hour) is typical. In sweltering conditions, sweat rates of greater than 85 fl oz per hour (2.5 liters per hour) can occur.  Holy shit!  That’s like carrying around a 2.5L bottle of Coca-Cola around with you on every long training session.  And then you add humidity to the equation as well?  Fuck me.

The formidable combination of heat and humidity poses a particularly serious challenge to thermoregulation during exercise because when you add humidity to the mix, the air is heavy with moisture.  If the air were dry, sweat would evaporate readily from the skin and a cooling effect would result.  But when the surrounding air is saturated with moisture, sweat doesn’t effectively evaporate from your skin during exercise.  Instead, it builds up and then drips off your body (or ‘cascades’, if you will, as was established in my recent fiasco in the hot yoga studio last week). As a result, you ultimately lose the cooling effect of sweat evaporation.  Scared yet?  I know I am.

This combination of high heat and humidity can put a serious damper (pardon the expression) on your ability to thermoregulate properly.  In these extreme conditions, you risk having the heat load build up to a critical level at which your body can’t function optimally.  At that point, you experience very strong signals from your body, asking you to stop exercising in order to lower your core temperature.  However, some athletes have been known to labor on and fight through these strong biological cues, only to end up suffering serious heat illnesses from the very high core body temperatures that result.  Yeah, that’s NOT going to be me.

Dehydration is another critical factor that influences your ability to cool yourself during exercise. When it’s hot out, sweating is the primary means for eliminating heat generated by contracting muscles, and sweat rates of 34–85 fl oz per hour (1.0–2.5 liters per hour) or more are common. However, for this cooling mechanism to function optimally, the fluids you’re losing as sweat need to be replaced. The problem is that during exercise, you typically don’t feel a sensation of thirst until after you’ve lost 1–2 percent of your body weight as fluid. That equates to 1.5–3.0 lbs of fluid for a 150-lb athlete (0.68–1.36 kg for a 68-kg athlete).  With that amount of fluid loss, you’re already in the throes of dehydration; your body’s ability to cool itself is undermined because dehydration results in decreased blood flow to the skin and a lower sweat rate.  Thus, both mechanisms for thermoregulation are compromised when you’re running low on fluids.

Fortunately, there are strategies you can employ to help you stay cool when training or competing in hot, humid weather.  Acclimating to the heat is an important one (hence my focus).

It is possible to acclimate to the heat by regular exposure to hot environments.  A key adaptation that occurs with heat acclimation is an increase in the volume of fluid that circulates in your body. With more fluid available, the heart pumps more fluid with each beat, and this leads to a lower heart rate during exercise.  In addition, less sodium is excreted in sweat and urine.  The extra sodium retained in your body is useful in maintaining an appropriate sodium concentration in the blood when the fluid volume expands. Interestingly, a low-sodium diet seems to impair the body’s ability to expand fluid volume.  So if you’re trying to acclimate to the heat, make sure you’re consuming adequate sodium. Two other critical adaptations include the onset of sweating at a lower core temperature and a higher sweat rate.  The increase in fluid volume and lower heart rate occur within about 3 to 6 days of daily heat exposure.  The decrease in sweat and urine sodium takes about 5 to 10 days, and the increase in sweat rate and the lower temperature threshold for the onset of sweating and dilation of blood vessels in the skin occur in 1 to 2 weeks.  What this all really means, it that for it to get any better than I just have to get out there and get sweaty – period.

Training sessions of about 100 minutes in hot conditions are most effective for inducing heat acclimation, and there is no advantage to spending additional time in the heat.  Also, exercising in the heat every third day for 30 days is the acclimatization equivalent of exercising every day for 10 days (my event is just over two months away, so better time than the present).  Keep in mind that heat acclimation is not permanent.  Effects gradually disappear if they are not maintained by repeated exposure to heat.  Adaptations start to disappear in about a week and are mostly gone within 30 days so maintaining this type of training regimen is going to be key…heat wave or no heat wave.

My biggest learning curve is around regulating my fluid intake.  You might guess that adapting to the heat would decrease my need for fluids, but in reality, the opposite is true.  Because you sweat sooner and at a faster rate when you’re acclimated to the heat, your fluid needs are higher. Researchers have found that after dehydration takes hold, core body temperatures are the same, whether or not you’ve acclimated to the heat beforehand.  So all those hard-earned advantages of heat acclimation are wiped out if you become dehydrated.

To stay hydrated during exercise, I’m consuming fluids at a rate that closely matches my sweat rate.  This typically falls in the range of 13 to 26 fl oz (400–800 ml) for every hour of exercise, preferably taken in smaller amounts every 15 minutes or so (therefore I always run with a hydration belt now where in the winter I wouldn’t bother).  However, fluid needs can vary considerably, so determining this sweat rate is the best approach.  It’s really quite simple, and it’s important to calculate your sweat rate for the various environmental conditions you will encounter, including hot and humid conditions.  To calculate your own sweat rate and to obtain a personalized plan to meet your own unique hydration needs, click on the Sweat Rate Calculator at

In summary, if heat and humidity are in the training or competition forecast, as it obviously is in my case, plan to acclimate to the conditions.  Check!  I can do that by training in a hot environment for about 100 minutes daily for 10 days, or at least 3-4 times a week for 4-6 weeks.  I need to remember to wear minimal clothing in the heat and make sure the clothes I wear doesn’t interfere with the evaporation of sweat.  Check!  Furthermore, I need to avoid dehydration by consuming fluids at a rate that closely matches your sweat rate.  And finally, stay hydrated with a well-designed, good-tasting sports drink that features sodium and carbohydrates.  Check! 

So, apart from all these easy-to-plan for contingencies, it really just comes down to another further example of simply getting out there and ‘Embracing the Suck’.

  1. mom says:

    No, I do not think you are crazy! I applaud your persistence and your determination to concur the heat! It makes my head spin to think about it.

  2. Jeff C says:

    Great post! Learned a lot. I’ve read that many runners over-hydrate as well yet I’ve also read that if you’re sweating really hard it’s almost impossible to stay hydrated no matter how much you drink (?)

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