Embrace the after-hours run or bike ride and you'll not only keep cool but also possibly amp up your results.
When people exercise in the evening, they are able to go 20 percent longer than they are in the morning, research in the journal Applied Physiology, Nutrition, and Metabolism found. Your body has a greater ability to produce energy in the evening, thanks to a faster oxygen uptake that spares your body's anaerobic reserves a bit longer, and your anaerobic capacity (how much energy you can produce without using oxygen) is at its peak at this time, explains David W. Hill, the author of the study. Nighttime exercisers also had larger increases in levels of cortisol and thyrotropin, two hormones essential for energy metabolism, than people who exercised at any other time of day, according to a University of Chicago study. When cortisol is running high all day because of stress, it can increase abdominal fat storage. But during exercise, cortisol does a 180, becoming a fat-burning hormone as it breaks down carbs more efficiently, says Michele Olson, Ph.D., an exercise physiologist at Auburn University at Montgomery. In other words, it turbocharges your calorie burn. Another study, in the Journal of Sports Medicine and Physical Fitness, compared women who walked for exercise in the morning with those who did so in the evening and found that even though both groups had roughly the same daily caloric intake, the women who walked later in the day burned more fat overall. Why? The evening exercisers experienced greater hunger suppression and seemed to opt for a more protein-rich postworkout meal, shifting the distribution of their daily calories to the morning instead; those actions were found to be protective against an increase in fat, says Andrea Di Blasio, the lead author of the study. Follow these strategies to work out better after dark and the results may convince you to stick with the night shift.
Start after sunset
It's not just the air that feels cooler at night; the ground does, too, says Patrick Cunniff, a cross-country and assistant track-and-field coach at the University of Georgia. When temps are in the 80s and 90s and the sun is shining, pavement and tracks can heat up to a sizzling 120 degrees. That heat radiates off the ground, making it feel as though you're running in a sauna, Cunniff explains. And high solar radiation raises the temperature of your skin, which forces your heart to work harder to try to keep you from overheating, thus sapping your endurance, new research in the European Journal of Applied Physiology revealed. To maximize your staying power and comfort, take off after dusk.
Build up a tolerance
"It takes only three to four sessions for your body to acclimate to the humidity of hot summer nights," says exercise physiologist Keith Baar, Ph.D., an associate professor at the University of California, Davis. Despite milder temperatures, relative humidity (basically, how much water the air holds) can be higher in the evening. This presents a sticky situation: Humidity causes you to sweat more and makes it harder to cool down, so any workout will feel harder than it should, according to research in the European Journal of Applied Physiology. Even though the lower evening temps mean you have less body heat to dissipate in the first place, the solution is to ease in with a few light exercise sessions. "Keep your pace one minute to 30 seconds slower than usual," Baar says; if you typically do a nine-minute mile, start out with a 10-minute mile and up your pace by 15 seconds per mile for each of the next three outings.
Divvy your dinner
Figuring out what to eat and when to fuel for evening exercise can be a challenge. Considering that sunset may start later than eight o'clock, should you squeeze in dinner before you head out? "It's best to have something that's about 200 calories and high in carbohydrates from grains, fruits and vegetables, or dairy; that contains some protein; and that's low in fat and fiber, and to eat it one to two hours beforehand," says Christy Brissette, R.D.N., the president of 80 Twenty Nutrition. If you like to eat on the early side, that could mean having part of your dinner before your workout and the rest after. Or if you typically eat later, opt for a snack such as yogurt with fruit or oatmeal with raisins or walnuts. Then an hour or so after your workout, eat a larger meal that has about 400 calories and about a two-to-one ratio of carbohydrates to protein. Try a burrito with chicken or black beans, brown rice, avocado, lettuce, and salsa in a whole-grain wrap, or soup, stew, or chili with a protein, veggies, and whole grains. And be sure not to skimp on vitamin D in your daily diet from foods like oily fish, milk, or fortified almond milk. If you're doing most of your summer workouts at night, you may be getting fewer of the sun's UVB rays, meaning your body is producing less of this vitamin, which improves muscle function, helps prevent injury, and lowers inflammation, Brissette says.
Don't hold back
Good news: You won't be cheating yourself out of any much-needed sleep by going hard during your work-out, even if you're cutting it close to bedtime, studies show. People who exercised vigorously for 35 minutes about two hours before bed reported sleeping just as well as on nights when they didn't exercise, according to findings in the Journal of Sleep Research. And when compared with morning exercisers, those who worked out at night actually slept more soundly and longer, a recent study at Appalachian State University found. "Evening exercise warms up your core body temperature, similar to taking a warm bath before bedtime," explains lead study author Scott Collier, Ph.D., "and that helps you to fall asleep quicker and to sleep better."
Limber up your senses
Before you dash, spend 10 to 15 minutes warming up outside so that your eyes can better adjust to the dark, suggests Fred Owens, Ph.D., a professor of psychology at Franklin and Marshall College. The more acclimated your eyesight, the safer you'll be: Evening road traffic is at its busiest from six to nine o'clock, making it the most dangerous time for pedestrians to be out, according to the National Highway Traffic Safety Administration. And we know you love your tunes, but it's best to ditch them so you can listen for oncoming traffic. If you simply can't seem to run without music, wear headphones that let in ambient noise—like the wireless AfterShokz Trekz Titanium ($130, aftershokz.com), which has an open-ear design—and keep the volume low.
Light up the night
If you run roadside, wear reflective materials, which are illuminated by headlights, Owens suggests. For trail or park runs, opt for glow-in-the-dark materials. They're the safest option, he says, because they'll shine even without exposure to external light. In both cases, the illumination or reflectivity on your clothes should be on the parts of your body that will be moving the most, such as joints, so drivers can more easily read the motion as that of a runner. Stick with the picks on these pages and you're covered.