More Health:

June 30, 2018

Exercising in the heat? Take these precautions

Penn doctor stresses early A.M. exercises, light clothing and plenty of water

Fitness Heat Wave
Stock_Carroll - Running on the Schuylkill River Trail in Philadelphia Thom Carroll/PhillyVoice

Two runners on a scenic path in Philadelphia.

The first heat wave of the summer is here.

The daily high temperature in Philadelphia is expected to hit at least 93 degrees for the next week, according to The National Weather Service

And the next three days will be particularly oppressive, with highs in the upper 90s and an excessive heat warning declared for most of Sunday and Monday.

That weather can be great for people heading to the shore or spending their afternoons at the swimming pool. But how can – or should – people maintain their regular exercise in such swelter?

Dr. Brian Sennett, chief of sports medicine at the University of Pennsylvania Health System, suggested that people committed to working out in extreme heat take a number of precautions.

"Everyone is excited about getting out there and doing something," Sennett said. "The heat is a lure. It's a draw to get out there and do stuff, but you need to be smart in decreasing your risk factors."


"The best way to beat the heat is to avoid the heat," Sennett said.

That means taking one of two approaches – either exercise indoors or work out during the early morning or evening. Avoid exercising outdoors between 10 a.m. and 3 p.m., which generally are the hottest hours of the day.

Sennett also suggested people break up lengthy exercises throughout the weekend – particularly if they have a history of heart problems.

"Don't go for a three-hour bike ride on Saturday," Sennett said. "Go for an hour ride on Saturday and an hour ride on Sunday. Then, do something else at a later time on those days. It gives your body time to rebound."

For athletes training for a triathlon, Sennett suggested opting for a swimming workout over a bicycle ride or run.


Avoid wearing dark clothing when exercising outdoors, Sennett said. Dark blues, greens and black all absorb sunlight, whereas lighter colors like lime greens, yellows and whites all reflect the sun.

Looser clothing dissipates heat better than tight clothing. Exercise gear that wicks moisture away from the body also will help people remain cooler. So will a brimmed hat that casts shade over your face.

"When you start exercising, your body is trying to dissipate heat," Sennett said. "Any way you can do that through convection, evaporation or cooling – all of these things are helpful."

Perhaps the worst idea, Sennett said, is to pull on a sweatshirt in hopes of burning more calories.

"These are not days to be thinking about burning a lot of calories," Sennett said. "Many times, when you think you're burning calories, you're just losing water."

Also, be sure to apply sunscreen to protect your skin from ultraviolet rays.


Hydration is essential during such high temperatures and humidity. It is helpful to not only know what to drink, but when to consume it.

Anyone exercising for less than an hour can opt for simply consuming water during the workout, Sennett said. But anyone exercising for longer than hour needs to replenish their sodium levels, which can become diluted by strictly drinking water.

"If you start exercising longer, your sweat demands are going to go up," Sennett said. "Then it's important to start replacing not only the water that you're using, but the electrolytes that you're losing."

Additionally, Sennett encouraged people to pre-hydrate. He also suggested they avoid consuming caffeine or alcohol both before and after their workouts because they act as diuretics, pushing fluid out of the body.


People who start to feel faint may be getting behind on their fluids. But Sennett stressed that people should not feel guilty about quitting partially through a workout – especially if they're not feeling great.

"You may regularly go for a five-mile run," Sennett said. "If you're not feeling quite right, there's nothing wrong with stopping and taking an Uber home."

With that in mind, Sennett encouraged people to carry money, credit cards or cellphones with them.

Headaches, nausea and lethargy are all early warning signs that something isn't quite right, Sennett said. Don't confuse them with fatigue, especially if they occur early in a workout.

"Sometimes feeling just fatigued can be the same as getting a heat illness," Sennett said. "If you are feeling fatigued in these hot weather conditions, be more concerned about it – that it may be more than just fatigue. ... Increase fluid intake (and) look for abilities to cool off, whether it's an air-conditioned area or a cold shower."

Also, expect to walk, run or bike at a slower pace during hot weather. Running an 8-minute mile is more taxing in 95-degree heat than it is during spring temperatures.

Monitoring a workout based on heart rate can be a helpful approach, Sennett said. To do so, try not to exceed the heart rate that you experience when exercising during cooler temperatures, even if that means your splits come in at a slower pace.

"Nowadays, with so many people wearing Fitbits and other heart-monitoring devices, it's really a great thing," Sennett said.

Follow us

Health Videos