Is It Too Hot To Run Outside? Here's How To Tell.

These five signs mean you should save those miles for later.

In plenty of places, the start of summer means sweltering heat. According to a study published in Nature, 2023 was the hottest summer in the Northern Hemisphere in more than 2,000 years.

This year is shaping up to be a scorcher, too. Cities in the Midwest, the Northeast and the mid-Atlantic are all experiencing extreme heat and humidity this week, factors that health experts say could lead to to heat exhaustion and heatstroke if you’re outside for too long. Heat-related deaths have been increasing in the U.S.: There were approximately 1,602 in 2021, 1,722 in 2022, and 2,302 in 2023.

Signs of heat illness include excessive sweating, nausea, cramps and confusion, said Meghan Kennihan, a National Academy of Sports Medicine-certified personal trainer and running coach. “Heat illness can escalate to heat exhaustion or heatstroke, which are life-threatening conditions requiring immediate medical attention,” she said.

If you’re a runner, it’s especially important to be aware of extreme heat conditions. “Running in the heat poses risks such as heat exhaustion, heatstroke, dehydration, and electrolyte imbalances,” Kennihan said.

What’s more, you’ll probably be running poorly if you’re overheated and pushing yourself too hard. “Your performance typically declines because your body prioritizes cooling over running efficiency,” Kennihan said. “Heat stress can reduce stamina, slow your pace, and increase perceived effort, making your usual run feel significantly harder.”