THURSDAY, JULY 20, 2017

The Saturday morning marathon training group's coaches and runners face a question for this weekend's training run: What to do about the heat?

Facebook posts have already been issued giving advice for running outdoors in very hot and humid weather: Slow it down, run very early, hydrate, take salt. All great advice. But when should you NOT run in the heat?

Core temperature

The physiology of heat is that when it gets hotter, your body diverts more blood to the capillaries of the skin in an effort to cool you down. The result? The muscles you use for running have less blood and thus function less efficiently. Running gets harder.

So when the temperature rises, you naturally slow down How much? Here's a blog post I wrote last year that offers the data. It shows, for example, that a person who at 60 degrees can run a 4:00 marathon - 9:09 per mile pace - will run the same distance using the same effort at 100 degrees in 4:14:24 - 9:42 pace, 33 seconds a mile slower

And then there is the double whammy of high humidity and higher temperature. The same blog post cites research that shows "exercise capacity at a moderate intensity in a warm environment is progressively impaired as the relative humidity increases." Body temperature further increases because higher humidity keeps sweat from evaporating as quickly.

Hydration

Hydration - drinking water or water-based drinks - is a necessary component for running in the heat. As you become progressively dehydrated (according to WebMD), symptoms you may experience include:

• Thirst

• Dry or sticky mouth

• Not peeing very much or at all

• Dark yellow pee

• Dry, cool skin

• Headache

• Muscle cramps

• Very dry skin

• Feeling dizzy

• Rapid heartbeat

• Rapid breathing

• Sunken eyes

• Sleepiness, lack of energy, confusion or irritability

• Fainting

Michael Gleeson, PhD, summaries in Sports Nutrition the effects of exercising while being dehydrated:

• Reduction in blood volume

• Decreased skin blood flow

• Decreased sweat rate

• Decreased heat dissipation

• Increased core temperature

• Increased rate of muscle glycogen use

• A reduced maximal cardiac output

Heat illnesses

The combination of heat, humidity and dehydration can lead not only to poor performance, but also to heat illnesses. The Centers for Disease Control has published this scary chart on heat illnesses:

Hyponatremia

Yet over-hydration can also lead to performance problems and equally disturbing results. I explored the dangers of hyponatremia - water intoxication - in a blog post on how much to drink. Researchers concluded that many runners were drinking too much fluid in longer races and training runs. With hyponatremia, you drink more than you sweat and urinate and dilute your blood’s sodium levels. The sodium imbalance can cause cells to swell, especially brain cells. In extreme cases, competitors died after drinking too much liquid during a race.

The most current guidance on hydration is to drink when thirsty, not excessively ahead of racing or training to "bank fluid" or to excess during the workout or race.

Electrolytes

The problem with just drinking water when running long is that you are adding to fluid volume in your body but you are not maintaining your electrolyte balance. Gu Energy Lab Notes offers a handy summary of why to ingest electrolytes as well as water while running in the heat and humidity:

• Replenishing electrolytes during exercise helps maintain plasma volume, which is depleted when you sweat. Hydration drinks with electrolytes help maintain plasma volume over time better than water alone (Anastasiou, 2009). Maintaining plasma volume will prevent decreases in performance associated with dehydration.

• Replacing electrolytes during exercise helps prevents hyponatremia from over-ingestion of fluids during exercise (Anastasiou, 2009, Twerenbold, 2003). Consuming electrolytes in a concentrated form such as in an energy gel will be most effective at combating hyponatremia. This is because intake of sports drinks alone can lead to hyponatremia since salt concentrations are more diluted than the blood.

• Consuming electrolytes may help prevent cramping during exercise. Some research (Seltzer, 2005) has shown that individuals who are prone to cramping tend to lose more salt in their sweat compared to athletes who do not cramp (Stofan, 2005), and salt replacement interventions have been successful at preventing cramping in some athletes (Bergeron, 2003).

Last August I did a deep dive into electrolyte options for endurance athletes. The blog post offers detailed information on 24 options: tablets, capsules, drinks and water supplements. I came up with three questions for selecting electrolytes to use in hot, humid conditions:

• Do you want capsules, tablets, powder, concentrated liquid or a pre-mixed drink?

• Are you mainly after the traditional sodium and potassium replacement, or a more complex blend of ingredients? And how much sodium (salt) should be in the mix? It's up for debate - with Hammer Nutrition (Endurolytes) being a leading advocate for not viewing lots of sodium as the answer. A related point: Is it true that calcium helps you avoid cramping?

• Will you get your carbohydrates (and perhaps protein) separately or do you want an all-in-one solution?

What I thought then still applies for me:

"For me right now, I am very comfortable with Endurolytes and Gatorade (with GU for added energy) - but if I were doing Ironman training and racing now I think I would want more sodium in the mix, given a high sweat rate over many hours, and I would be more interested in a one-product solution.

"While I can cope with using Endurolytes, Gatorade, Gu and water while marathoning (with me carrying the Endurolytes and Gu and the race or the training program typically putting out the Gatorade and water), again, if I were in Ironman mode I might look at Infiniti:GO FAR, maybe even a customized formula, or at another nutrition option with appropriate electrolytes included."

Your own body

Different individuals have varied response to heat and humidity

First, your size will make a difference in how you are affected by hot and humid conditions. Runner's World cites a study by renown running physiologist Timothy Noakes showing that the larger you are, the more strongly you will be affected by heat—so adjust your pace appropriately. In Noakes' study, he tested lighter runners (110 lbs. or less) and slightly heavier runners (averaging 130 lbs.) who in cool conditions had identical 8K times. When the temperature was increased to 95 degrees, the larger runners were 45 seconds per mile slower.

Second, your level of acclimatization to hot and humid conditions can make a big difference. Physician/runner Bill Henderson in his IRUNFAR blog offers this chart showing how long it takes for our various physiological systems to adapt to on-going heat and humidity - to the extent that they can adapt, of course.

Henderson writes, "The most significant change that occurs is an increase in plasma volume. Other things occur as well (such as changes in sweat sodium concentration, resting core temperature and heart rate), but plasma volume expansion is the key. After extensive acclimatization, plasma volume can have expanded by as much as 2 liters!"

You will acclimate naturally to higher temperatures over the course of a season, but laboratory heat acclimation protocols put athletes in a heat chamber for about 1 hour a day for 7-10 days. Acclimatization is vastly greater (and more rapid) if you exercise in the heat. Generally it takes about two weeks of continual training in the heat to acclimatize.

Unfortunately, if you stop heat training you will begin to de-acclimatize and can lose what you have gained within a couple of weeks.

Time of day and place

When and where you run in hot, humid weather can make a difference.

It may be obvious but it is worth stating:

• Run very early in the morning or late at night, when it is cooler and, hopefully, a little less humid.

• Run in the trees and in shade rather than in the sun.

• Run on grass or another cooler surface than sun-blasted asphalt or concrete, in the shade if possible.

If your normal course takes you from a shady trail to an exposed highway out-and-back, as mine will this weekend, change the route to avoid the hotter, exposed portion of the course.

To run...or not?

So back to the question: Is this a time when we should NOT run in the heat?

While I am helping out our marathon training coaches this season, it's not my call on whether the group runs on Saturday morning, and if it does, what time the run starts and how the course might be modified, if at all.

What my homework on running in heat and humidity says to me is that all who run in hot and humid conditions should properly hydrate, use appropriate electrolytes and be happy with a slowed pace. They should monitor themselves and their running partners for the signs of heat illness. They should seek a shadier, cooler route and start as early in the day a feasible.

Running buddy Henry and I have tentatively planned to start our 17 mile run with the sunrise at 5:30 am on Saturday. We will cut out the more exposed part of our trail course. We expect to be slow. And we'll be ready to shorten, abandon or not even start the run depending on the weather and our response to the conditions.

My story

I learned my lesson about not being acclimated and prepared for the heat when a planned 20 mile run became a very difficult 16 mile effort in unanticipated heat. I crashed bad with some heat exhaustion symptoms afterward. Here's the story if you want to learn what not to do!

If you run in the heat, be wise about it. If you don't, likely that's the right decision for you!

June 2018 update: Here's another run blogger's take on running in the heat and humidity, with useful information and some good product suggestions. My recommendation to you on the products, however, is to support your local running shop and buy them locally if possible.