Memorial Day, the unofficial start of summer. Time to review the protocols of summer weather exercise.
The Human HVAC System 101
When discussing the body’s natural cooling system, a smart phone on a battery-saver setting is an apt comparison. A phone on this setting will give priority to the most important functions and shut down less necessary functions as it gets low on power.
Similarly, keeping the core temperature within the normal range is a major priority for the human body. The brain knows a rise of two or three degrees in core temperature can lead to heat stroke and heat exhaustion. Both will cause acute illness and can lead to organ failure and even death. To avoid this, the body will shut down less necessary functions. This process first triggers symptoms, like cramping and dehydration, that signal it’s time to stop activity to avoid real damage.
In addition, the body employs its natural cooling system. Sweat glands are signaled to release water on the skin’s surface. Cooling comes not 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.
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.
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, reducing calorie burn, to keep the cooling system from being overrun. The more hot and humid the conditions, the faster you’ll experience those first warning signs – cramping and dehydration. 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.
If you workout indoors in an un-air conditioned environment, it’s essential to use fans blowing directly on the body to assist the evaporation process when temperature and humidity levels are high.
Heat & Humidity Exercise Guidelines
- Hydration: 2 hours prior to exercise drink 17-20 oz of water. Sip water while exercising – approximately 7-10 oz every 10-20 minutes. Following exercise, drink 16-24 oz for every one-hour period of your workout. In this circumstance, it’s okay for a recreational exerciser to have a sports drink post-exercise that contains 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 and apply sunscreen to all exposed skin. Wear UV proof sunglasses and/or 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. Keep an eye on the sky and forecasts, high heat and humidity increases the likelihood of dangerous storms.
- Intensity: Avoid any high-intensity exercise. These are the days to do low to moderate intensity, shortened workouts. Save your best runs, power walks and steepest cycling hills for a cooler day.
DECONDITIONED or those with CARDIOVASCULAR or PULOMONARY CONDITIONS: Avoid all outdoor workouts and non-A/C indoor exercise 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 and non-A/C indoor 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.