This weekend is Memorial Day weekend – the unofficial start of summer. Which means three H weather (hazy, hot & humid) is right around the corner. Time for my annual hot weather workout rules of engagement.
To understand the body’s natural cooling system, consider a smart phone on 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 to divert energy to the cooling process.
Cooling happens when sweat glands are signaled to release fluid onto the skin’s surface. Cooling doesn’t come directly from the sweat but, rather, from the evaporation of the perspiration. Any environment that excessively heats the body or impedes evaporation puts a strain on this system. The more the system is taxed, the greater the risk it will fail.
High temperatures aren’t the only concern. High humidity is a greater threat. Wet, heavy, still air impedes the evaporation process. So, while running in 90° weather in the arid desert is risky, running in 85° weather in 85% humidity with no wind is riskier.
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. Use fans and observe the hot weather guidelines and rules listed below.
THERE IS NO CORRELATION BETWEEN SWEAT & CALORIE BURN
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 muscle 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 compared to lying on your couch and here’s why.
The body’s energy production releases heat as a by-product of burning calories. So, when the environment is very hot or humid, the body must slow or stop internal heat production. Whether you sunbathe or run at noon on a 90° day, your body will slow metabolism to reduce calorie burn and divert that energy to the cooling process.
It may feel like you’re getting a great workout on a hot day, but your exhaustion comes from the brain demoting the cardiovascular system and working muscles, giving the cooling system first priority. The more hot and humid the conditions, the quicker the diversion process kicks in. This isn’t a productive workout. On the contrary, it’s risky with none of the rewards.
HOT WEATHER EXERCISE GUIDELINES
HEALTHY, REGULAR EXERCISERS ONLY: Follow the 4 Rules (below) when WBGT is 82-89°F; Avoid outdoor exercise when WBGT > 89°F
DECONDITIONED/CARDIOVASCULAR or PULMONARY CONDITIONS: Follow the 4 Rules (below) when WBGT is 75-80°F; Avoid outdoor exercise when WBGT > 80°F
THE FIRST SIGNS THE BODY’S COOLING SYSTEM IS FAILING ARE CRAMPING AND DEHYDRATION. IGNORING THESE EARLY WARNINGS IS A RECIPE FOR HEAT EXHAUSTION OR, WORSE, HEAT STROKE:
THE 4 RULES OF HOT WEATHER ENGAGEMENT
#1: Avoid the hottest time of day (11am-5pm): 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 increase the likelihood of dangerous storms.
#2: Dress the part: 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. 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.
#3: Hydrate, hydrate, hydrate: 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 very hot/humid conditions, it’s recommended to include sports drinks to replenish sodium and other electrolytes lost during perspiration.
#4: Select the correct intensity: Avoid any high intensity exercise. Perform low to moderate intensity, shortened workouts. Save your fastest and longest runs, power walks and steepest cycling hills for a cooler, drier day.
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 workout in a climate controlled environment
- Swap your rest day for the week
Be smart and healthy on those three H days and be fit and happier all summer long.