Physiology

When summer starts with a stifling heat wave, as many places are seeing in 2024, it can pose risks for just about anyone who spends time outside, whether they’re runners, people who walk or cycle to work, outdoor workers or kids playing sports. Susan Yeargin, an expert on heat-related illnesses, explains what everyone should think about before spending time outside in a heat wave and how to keep yourself and vulnerable family members and friends safe. What risks do people facing running, walking or working outside when it’s hot out? The time of day matters if you’re going for a run, or if you’re walking or cycling to work during a heat wave. Early risers or evening runners face less of a risk – the Sun isn’t as hot and the air temperature is lower. But if your normal routine is to go for a run midmorning or over lunch, you probably want to rethink exercising in the heat. Pretty much everywhere in the U.S., the hottest part of the day is be...

For three weeks in July, the world’s most elite bike racers climb steep mountains and sprint along historic cobblestones to capture the coveted yellow jersey or the race leader in the Tour de France. It’s a 21-day feat of human endurance that requires constant eating and drinking to manage the average daily energy demand of about 6,000 calories, equivalent to around 12 McDonald’s Happy Meals, and just over 1.5 gallons of water. Nearly 5,000 miles away in the mountains of North America, radios crackle with chatter from a wildfire incident command post, air operations and other crews fighting a wildfire. Up the fireline, the swings of Pulaskis, axlike hand tools, are carving a fuel break into the land. The weather forecast predicts a high of nearly 100 degrees Fahrenheit (38 C) with wind, a combination that can push the fire high up into the canopy of dense lodgepole pines on the mountainside. The yellow jerseys here are sooty, sweat-stained and flame-resistant...