Summer officially begins this Wednesday, June 21, at 12:24am. That means it’s time for my annual reminder about safe exercise when Mother Nature turns up the heat.
HUMAN HVAC SYSTEM 101
To understand the body’s natural cooling system, consider a smart phone on a battery-saver setting. This setting will give priority to the most important functions and shut down less necessary functions as it gets low on power to avoid complete system failure.
Similarly, keeping the core temperature within the normal range is a priority for the human body. The brain knows a rise of a few degrees in core temperature can lead to heat exhaustion and heat stroke. Both will cause acute illness and can lead to organ failure and even death. To avoid this, when the environment heats up, the body will slow or shut down less necessary functions and divert energy to keep temperature normalized.
Cooling happens when sweat glands are signaled to release water on the skin’s surface. Cooling doesn’t come directly from the sweat but, rather, from the evaporation of the perspiration. Anything that impedes evaporation puts a strain on the body’s cooling system. The more this system is taxed, the greater the risk it will fail.
The very first signs that the body is having trouble keeping cool are cramping and dehydration. Ignoring these early warning signs is a recipe for heat exhaustion or, worse, heat stroke.
RULES OF HOT WEATHER ENGAGEMENT
#1: Avoid the hottest time of day: There is no correlation between sweat and number of calories burned.
It’s true an elevated heart rate during exercise induces more sweat and calorie burn than a body at rest. But, calorie burn is related to work output, not sweat generation. For example, run on a cold day and you’ll perspire and burn calories. But, you’d probably sweat just as much lying on the beach in July. There’s no excess calorie burn while sunbathing even though perspiration is high. In fact, you may burn fewer calories lying on the beach as compared to lying on your couch and here’s why.
The body’s energy production releases heat as a by-product of burning calories and, when the environment is hot, the body will produce less internal heat to keep cool. Whether you sunbathe or run at noon on a 90 degree day, your body will adjust its systems to cool the body while expending the fewest calories possible.
It may feel like you’re getting a great workout on a hot day, but the exhaustion you feel comes from the body diverting its resources away from the cardiovascular system and muscles to reduce calorie burn and rev up the cooling system. The more hot and humid the conditions, the quicker the diverting process kicks in. This isn’t a productive workout. On the contrary, it’s risky with none of the rewards.
#2: Don’t overdress: Remember, the body cools not from the sweat itself but from the evaporation of sweat off exposed skin. Covering skin impedes evaporation. The hotter, more humid the day, the more exposed skin you should have.
#3: Beware humidity: Wet, heavy, still air impedes the evaporation process. Dry, breezy air is conducive to evaporation. So, while running in 90 degree weather in the arid desert is risky, running in 85 degree weather in 85% humidity could be deadly.
Both heat and humidity need to be taken into consideration before deciding to exercise outdoors. Weather websites and apps post current temperature and relative humidity. An easier indicator to use is a third number often posted, sometimes called the “feels like”, “real feel” or the wet bulb globe temperature (WBGT). WBGT is derived from a formula that takes into consideration temperature, humidity and radiant heat.
By the way, the same rules apply if you’re working out indoors without air conditioning. Using fans can aid the evaporation process but care should be taken to keep workout times shorter and intensities lower in very humid conditions.
HOT WEATHER EXERCISE GUIDELINES
HEALTHY, REGULAR EXERCISERS ONLY: Take precautionary measures when WBGT exceeds 82 degrees:
- Hydration: Two hours before exercise, drink 17-20 oz of water. Sip 7-10 oz of water every 10-20 minutes while exercising. Afterwards, drink 16-24 oz for every one-hour period of your workout. Under these circumstances, it’s recommended to include sports drinks that contain sodium and electrolytes which are also lost when we perspire.
- Attire: Wear shorts, sleeveless or short-sleeved top, and short socks made of synthetic, light-colored fabrics that wick away moisture. Apply sunscreen to exposed skin. Wear UV proof sunglasses, brimmed hat or visor.
- Time of Day: Avoid the hottest time of day when sunlight is direct and shade is in short supply – 11am to 5 pm. Opt for right after sunrise or just before sunset when the sun is low on the horizon. Watch the sky and consult weather forecasts, high heat and humidity increases the likelihood of dangerous storms.
- Intensity: Avoid any high-intensity exercise. Perform low to moderate intensity, shortened workouts. Save your best runs, power walks and steepest cycling hills for a cooler, drier day.
DECONDITIONED or those with CARDIOVASCULAR or PULOMONARY CONDITIONS: Avoid all outdoor workouts as WBGT exceeds 80 degrees: Individuals in these categories are especially vulnerable. Opt to exercise in air conditioned indoor environments instead. Follow the above precautions for hydration, attire, time of day and intensity when WBGT is in the 75-80 degree range.
EVERYONE: Avoid outdoor workouts when WBGT nears or exceeds 90 degrees: If you’re a regular exerciser, being forced to change things up courtesy of Mother Nature can be a positive thing. It’s a fitness boost to introduce unfamiliar workouts on different days. Some alternatives to your regular workout when it’s too risky to do the status quo:
- Get a day pass for a nearby gym
- Do a lap swim workout at the local pool
- Sample a studio yoga or Pilates class
- Do an online cardio-strength training workout in an A/C environment
- Swap your rest day for the week
Be smart and healthy on those oppressive days and be fit and happier all summer long.