Running in the Heat & Humidity

Working Out in Hot Weather Can Lead to Dehydration and Heat Stroke

Photo of Kelly R. Smith   by Kelly R. Smith

Running in the summer heat
Running in the summer heat
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If there’s one thing runners in Texas understand, it’s heat. Some seem to tolerate it more than others, but too much of it can be deadly. Have you ever wondered exactly how and why it affects you like it does? OK; let’s look into that. It’s a completely different animal than cold weather running. Here are factors to focus on.

  • Thermoregulation. This concept involves maintaining adequate heat production and sufficient heat dissipation; a balancing act, essentially. Your normal skin temp: 33°C (91°F), range 32-35°C. MedlinePlus.gov says, “Some studies have shown that the “normal” body temperature can have a wide range, from 97°F (36.1°C) to 99°F (37.2°C). A temperature over 100.4°F (38°C) most often means you have a fever caused by an infection or illness.”1 But during strenuous exercise the body’s heat production may exceed 1000 W. Some of the heat produced is stored, raising body core temperature by a few degrees. Evaporation of your sweat and an increased skin blood flow are highly-effective mechanisms for the dissipation of heat from the body, however dehydration hampers your ability to sweat and lose body heat.
  • Exercise. Your core temperature increases during exercise in relationship to exercise intensity. Obviously, a slow, easy run will have less effect than speedwork. Heat production is 15-20 times greater than when you are at rest. It has been said that it’s a blessing in the wintertime, and a curse in the summer. Why is it harder to get a head of steam up on hot days? As much as 70% of energy produced is released as heat instead of energy for muscles. This causes an increase in core body temperature by 1°C for every 5 minutes of exercise without heat loss.
  • Heat and humidity. Your heart rate increases up to 10 beats per minute when the temperature is in the range 75-90°F. Your heart rate increases up to additional 10 bpm when humidity is 50-90% because of decreased evaporation. Your performance can decrease by ~20% when temps are above 80°F.


  • Heat dissipation. What areas of body are most important for heat dissipation? Your forehead for one Do you wear a bandana or a cap? Your upper limbs, trunk, and lower limbs are next in line. I’m a big fan of going shirtless or wearing a wicking or cooling shirt like the one below.

Heat is transported by blood from muscles to skin primarily by sweating. This is the first step in the cooling, evaporation process. 75% of evaporated fluids comes from your skin and 25% from respiration (breathing). ScienceDirect.com tells us, “In humans, roughly 1.6 to 5 million sweat glands are found in the skin, and the amount varies between individuals as well as anatomic sites. The region with greatest sweat gland density is the palms and soles of the feet, which contain 600–700 sweat glands/cm2. The primary function of sweat glands is to keep the core body temperature at approximately 37 °C by releasing sweat in a hot environment or during physical activity.”2 So, your soles don’t help matters much. We sweat an average of 1.4 L/hr (max 3 L/hr). Don’t forget to re-hydrate. By the time you get thirsty you are already behind the ball. Use a large water bottle; fill it with filtered water before you leave home.

Your body also dissipates heat by increased skin blood flow (convection). It transfers heat from your core to your skin and stimulates the sweat response.



  • Heat related illnesses. According to the CDC, “Heat-related deaths and illnesses are preventable. Despite this fact, more than 600 people in the United States are killed by extreme heat every year.”3 There are 3 main types of heat-related illness that get progressively more serious. The first is heat cramps-sharp stabbing pain typically in legs or diaphragm. This is caused by electrolyte deficiencies/imbalances. The common treatment is to stop running, ingest a sports drink to replace fluids/electrolytes, and cool your body. The second illness is exertional hyperthermia. Symptoms are a core temp 39-40°C (102.2-104.0°F); excess sweating causing fluid volume loss of 6-10% of your body weight; headache, nausea, vomiting, fatigue, and an elevated heart rate (a real issue for those with high blood pressure). The treatment? all the things mentioned above plus cooling the body via immersion and elevating feet above level of the heart. The third illness is exertional heatstroke. This is characterized by all of the symptoms mentioned above plus core body temperature greater than 40.5°C (104.9°F), mental changes such as confusion, disorientation, and loss of consciousness. Seizures and coma are also likely, and in especially bad cases, death. Treatment includes all of the above but do not take fluids if unconscious/severely disoriented/seizing, etc.
  • Are there risks factors for developing a heat related illness? You bet! These include low fitness level, dehydration, being unacclimated to heat and humidity, overweight/obese (BMI or Body Mass Index greater than 27), medications or supplements, and even lack of sleep.
  • Prevention methods. The first thing to do is be realistic and adjust your pace. Refer to this chart.
Running pace adjustment due to heat and humidity
Running pace adjustment due to heat and humidity

Take walking breaks regularly and often, especially during your weekend long run. Hydrate, hydrate, hydrate. Thirst is not an accurate indicator of dehydration but increased HR and dark urine are. Your body absorbs liquids best when they’re cold (40℉ is ideal); cold fluids will also help reduce your core temperature. Take liquids with electrolytes, eat small amounts of foods w/sodium 12 hrs before running. Acclimate yourself to warmer weather beginning in the spring. 2 weeks of moderate intensity exercise, 30-100 min in duration in the heat, is a good rule of thumb. Keep to a regular schedule; adaptations can be lost in as little as 10 days. Trade in your hat for a visor.

These are the basics of running in the heat and humidity. A little common sense and precautions can go a long way. Above all, have fun; running is good for the soul!

References

  1. MedlinePlus.gov, Body temperature norms, https://medlineplus.gov/ency/article/001982.htm
  2. ScienceDirect.com, Sweat Gland, https://www.sciencedirect.com/topics/medicine-and-dentistry/sweat-gland
  3. Centers for Disease Control and Prevention, Extreme Heat, https://www.cdc.gov/disasters/extremeheat/index.html

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About the Author:

Photo of Kelly R. SmithKelly R. Smith is an Air Force veteran and was a commercial carpenter for 20 years before returning to night school at the University of Houston where he earned a Bachelor’s Degree in Computer Science. After working at NASA for a few years, he went on to develop software for the transportation, financial, and energy-trading industries. He has been writing, in one capacity or another, since he could hold a pencil. As a freelance writer now, he specializes in producing articles and blog content for a variety of clients. His personal blog is at I Can Fix Up My Home Blog where he muses on many different topics.

Find Your Best Race Distance

by Kelly R. Smith

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Start of the Houston Half Marathon
Start of the Houston Half Marathon

This article was updated on 12/02/20.

As runners, whether as beginners or with years of experience, most of us have our favorite race distances. The basis for that may be fitness level, physical limitations, or just good old personal preference. I have been running since 1975 so I’ve indulged in most of them. Here is what I’ve found out along the highways and byways.

Preparation and Training

No matter what distance you are focusing on or what specific event you are getting ready for it is important to stay healthy. This includes proper nutrition and avoiding overuse injury. In my case this also includes taking meds for high blood pressure. I have learned to deal with the side effects which took a bit of experimenting.

Should you take supplements? Another personal decision. It seems like every month a new “study” proves that they do or don’t help. I take Osteo-bi-Flex for my joints and I think it helps. I also take a multi-vitamin daily to edge my bets. I also take a CoQ10 supplement daily for a wide range of benefits.

What constitutes a “healthy lifestyle” can be a bit arbitrary but I have condensed some of my favorite tips (habits) of successful runners. Feel free to take the ones that work for you and dispense with the rest. As for training, it’s good to develop a weekly mileage base. A minimum of 20 miles per week is good for most people. After that, tailor your workouts to the distance your are specifically training for.

Running Track Events

Now This is Having Fun!

Track events can vary from very short sprints to longer distances like the 10K or the steeplechase. I’ll be honest; these are not my favorite races. They just hurt too much and the training is boring. Don’t get me wrong; I don’t mind doing speedwork and intervals one day a week but not for the bulk of my training. I would rather be out on the roads or trails.

Of course a lot of this has to do with your DNA. Runners who have inherited predominately fast-twitch muscles may find these events fun, but alas, I fall on the other end of the spectrum.

The Ever-Popular 5K Race

There are many reasons why the 5K is so popular. It is well within the reach of beginning runners, it’s easy to stage as a local fund-raiser, and it ties in nicely with holidays like Thanksgiving and Labor Day.

Training for this distance is not overly involved. I would recommend the following per week:  one speedwork workout, one long run of 6 to 10 miles, three runs of 3 miles, and one cross-training workout of personal choice (swimming, cycling, hiking, weights, yoga, ect.)

The race strategy is a short warm-up before the race to loosen up the muscles, going out confidently when the gun goes off, and then ramping up the pace. At a mile and a half in you should be breathing hard but not dying.

The 10K as a Middle-Distance Race

Whereas 5Ks can be considered any-weekend, any-community events, 10K races are a little harder to find. They are harder to stage requiring more police cooperation, more port-o-potties, and usually a stricter time limit so the police can go home and the volunteers can get the cones off the route.

Training for this distance is basically the same routine as the 5K with the distances bumped up. Mid-week runs should be 4-5 miles and the weekend long run should approach 8 miles.

My strategy for this distance is no warm-up, position myself about halfway back in the pack, go out easy at a conversational pace, and begin to ramp it up. Once the pack thins out to allow some maneuvering I do so passing when I can but not wasting energy. The last half mile should have you breathing heavily and of course when you can see the finish line you should be sprinting. You can generally find some other poor soul to lock horns in battle with.

Bumping It Up to the Half Marathon

This is my favorite distance. Finding a half usually requires a road trip of some sort unless you live in or near a larger community. These are usually fall races so you really need to start ramping up your training plan mid-summer or so.

The most important part of training is your weekly long run. Because of the time involved in the actual run and the subsequent relaxing and socializing, Saturday or Sunday are good choices. You should be doing upwards of 15 miles two weeks out from race day. Carry lots of water! I like a running water bottle belt. The one in the picture below is the one I use. The angled bottle ensures that a tall bottle won’t rub the hide off your spine like the straight up-and-down ones tend to do. Hide water bottles along your route if you need to. Use Body Glide or an equivalent to avoid chafing. It only takes one session of agony in the last couple of miles to make one a believer!

The week prior to the event you should do some serious tapering. Just a few miles for your midweek runs, and of course, no long run. As far as race strategy goes I just like to have fun. Go out very easy and settle into a good conversational pace. Beginning at about the halfway point I walk the water stations and mix a cup of water with some Gatorade; the full-strength stuff is just too much. I should mention here that not all races use Gatorade. Find out in advance what brand of sports drink they will be serving up and train with that. Run the tangents. You would be surprised how cumulative those extra few feet on every corner are.

Run a Full Marathon

How many times have you heard non-runners say a marathon is on their bucket list? My guess is that most of those buckets never get filled! But for runners there is really nothing bucketeseque about a full marathon; it’s just another notch on the old belt. Like when the guy at the office asks, “So, what did you do fun over the weekend?” To which you reply, “Oh, not much; just went for a run with 8,000 of my closest friends.” No small wonder that sedentary people think we’re crazy.

The training and strategy are basically the same as for the half  but there’s just more mileage involved. I always allow about six months of ramping up my training. Of course, following the 10% rule (no more than 10% weekly mileage total per week; no more than 10% increase in long run distance every other week). The weeks between long  runs should now be 10-12 miles in length.

Ready to Step it  Up to an Ultramarathon?

This is Me at the Sunmart Ultramarathon

I’ve done the Sunmart Ultra 5 times and enjoyed every one of them. The hardest thing for me was the psychological aspect. The distance for me was not the issue, it was the fact that it was a multi-loop course after the initial 10K segment. Every time I went through the check-in station it was, “Oh Lord here we go again.” The upside is that you meet some really nice people.

The training was almost the same as for the marathon except for the enormous amount of mileage I had to put in for training. In fact, many times I had to break up my long runs between Saturday and Sunday. That started beginning when my scheduled long run called for over 20 miles. Even starting a couple hours before dawn that South Texas sun would take its toll.

With this volume of weekly distance, allowing adequate time for running recovery became critical. At that time I was also very active with triathlons and quickly found out that long, slow lap swimming was my friend. It’s really like a massage.

So there you have it; these are some of the things I have learned over the years. Take from it what you will and I hope some of it will help you and contribute to avoiding injury. We are all built differently and that’s why there are so many training concepts, no matter what you discover to be your best race distance.

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About the Author:

Photo of Kelly R. SmithKelly R. Smith is an Air Force veteran and was a commercial carpenter for 20 years before returning to night school at the University of Houston where he earned a Bachelor’s Degree in Computer Science. After working at NASA for a few years, he went on to develop software for the transportation, financial, and energy-trading industries. He has been writing, in one capacity or another, since he could hold a pencil. As a freelance writer now, he specializes in producing articles and blog content for a variety of clients. His personal blog is at I Can Fix Up My Home Blog where he muses on many different topics.

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