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We might be past the so-called dog days of summer — July 3 to August 11, the time when Sirius, the Dog Star, is most closely aligned with the sun and we expect summer’s heat to be its most intense — but when it comes to exercising outdoors, we have to pay attention to more than just the temperature.
Rob Green, owner of Active Recovery + Performance, a board-certified chiropractor and a veteran of more than 20 Ironman competitions, notes that heat and dew point together have a significant effect on our ability to exercise safely while chasing training goals.
“Dew point is the first and most important number I check [before training outdoors],” Green says, adding that everyone has to acknowledge and accept the conditions before them. “July and August are bad for runners’ self-esteem,” he says. “Even though you’re training, you feel like you’re slowing down.”
While humidity — the amount of water vapor in the air — is often blamed for discomfort, we also need to pay attention to the dew point, the temperature at which air can hold no more water. The National Weather Service notes that when the dew point is less than or equal to 55, weather conditions are pleasant. A dew point between 55 and 65 will feel sticky. Once the dew point is above 65, there’s so much moisture in the air that the outdoors will feel oppressive. You can find dew point on most weather apps or at the NWS website by entering your ZIP code.
Green recommends a pacing guide (see below), shared on his business’ Instagram in July, that takes into account temperature and dew point. The sum of the two numbers indicates when pace should be adjusted. If the combined number is 100 or lower, your regular pace is reasonable. As the number increases, however, you should decrease the pace incrementally. Once that number hits 180, Green suggests you save the intense workout for another day.
“The harder you work, the more your core temp rises,” he says. “If you can’t disperse the heat, you run into trouble. That’s why dew point is so important. Evaporation cools the body, and when you can’t evaporate well, you can’t cool efficiently.”
Any time we exercise, we need to pay attention to what our bodies are telling us, says Emily Huss, VCU Health Sports Medicine lead athletic trainer. “Heat does not discriminate between lesser prepared populations and more active populations,” she says. “You have to know the risks of pushing yourself too hard in the heat.”
Heavy sweating, muscle weakness and fatigue are all indicators of heat exhaustion, Huss notes. Less common symptoms include dizziness, headache, nausea or vomiting, which can indicate severe dehydration. When she works with athletic teams as a trainer, Huss has players weigh in before and after workouts, so it’s clear how much water weight they’ve shed during the workout. She recommends the same practice for anyone heading into strenuous exercise. “Being able to see how much [weight] you’ve lost easily translates into how much water you need to replenish,” she says, adding that for every pound lost, a person should add 32 ounces of water to that day’s consumption.
Huss also recommends regular hydration breaks during workouts based on the “feels like” temperature available on most mobile phone weather apps. If the temperature feels like 90 degrees Fahrenheit, plan for a water break every 15 to 20 minutes. Once the temperature feels like 94 degrees, break at 10 minutes. Over 100 degrees, move exercise indoors.
“If you are properly hydrated and listening to those warning signs, you are prepared enough to avoid a real emergency situation,” such as heat stroke, Huss says. Heat stroke can be indicated by confusion, physical collapse and dizziness to the point of altered consciousness and demonstrates a collapse of the central nervous system.
“My general recommendation is everything in moderation,” Huss says. “Our bodies require and really thrive when we are given rest and recovery days. Our bodies are not meant to be pushed seven days a week. There are ways to be active every day if that is what your goal is: yoga for flexibility, swimming uses water for resistance, weightlifting.”
Green agrees that hydration is important and notes that in the summer, it’s wise to add a supplemental powder containing sodium and electrolytes to your water bottle. “You need a focused, long-term hydration plan,” he says. “Electrolytes help you retain water. If you don’t have an electrolyte program or supplement, you will have a near-impossible job of keeping up with heat in the summer.”
Part of training effectively, Green says, is knowing your body. “If you stopped every time [training] got tough, you’d never do what you want to do,” he says. “I say it’s like being a fighter pilot who has to know how to read the gauges. Accept the conditions and know the signs [of distress]. Your long-term health is what’s important.”
