Training for a marathon in the summer presents unique challenges—but with the right approach, you can stay safe, build endurance, and make the most of your miles. SSM Health sports medicine physician Dr. Katherine Fox says a few smart adjustments can make all the difference when running in the heat.
Smart scheduling
As enjoyable as sunny summer runs can be, it’s important to start any warm-weather training block with proper acclimatization—the process by which your body adapts to exercising in the heat. Gradually exposing yourself to higher temperatures helps your body regulate heat more efficiently over time.
One of the simplest ways to support acclimatization is through smart scheduling.
“It’s really helpful to avoid the hottest parts of the day when you can,” said Dr. Fox. “Exercising during peak heat makes it harder for your body to cool itself as quickly as it warms up.”
Dr. Fox recommends planning outdoor workouts in the early morning or evening hours, when temperatures and sun exposure are lower. Not only will this reduce strain on your body, but it can also help improve performance and overall comfort.
Drink up
Hydration is essential year-round, but it becomes especially critical during summer training. Higher temperatures increase sweat loss, which means your body needs more fluids—and electrolytes—to function properly.
Start by drinking one to two glasses of water before you run. During longer or hotter workouts, consider carrying water or using a hydration pack so you can sip regularly—about every 10–15 minutes—even if you don’t feel thirsty. Dr. Fox also notes the importance of replenishing glucose and electrolytes.
“When sweat loss increases on long, hot runs, your body loses key minerals like sodium and potassium much faster,” says Dr. Fox. “This can lead to muscle cramps, fatigue, and dizziness. Replacing those electrolytes helps maintain fluid balance, nerve function, and performance.”
She notes that drinking water is sufficient for workouts that are shorter than 60 minutes. If your workout lasts longer than an hour, you need a sports drink or electrolyte mix.
Stay weather wise
Summer weather can bring unpredictable—and sometimes dangerous—conditions for runners. Staying aware of the forecast is an important part of protecting your health.
Avoid running during thunderstorms, when lightning, slick surfaces, and reduced visibility increase the risk of injury. Heat and humidity also require careful attention.
When humidity rises above 70%, sweat evaporates more slowly, making it harder for your body to cool itself. This can significantly increase your risk of heat-related illnesses.
“Pay attention to the heat index, which combines temperature and humidity to show how hot it actually feels,” said Dr. Fox. “For many runners, a heat index of 90 degrees or higher is too extreme for safe outdoor exercise.”
On these days, consider shortening your workout, adjusting intensity, or moving training indoors.
Know your limits
Even with the best preparation, some runs won’t go as planned—and that’s okay. Recognizing your body’s warning signs and knowing when to stop is key to preventing more serious conditions like heat exhaustion or heat stroke.
If you experience any of the following symptoms, stop running immediately and find a cool place to rest:
- Pale or clammy skin
- Headache
- Dizziness or lightheadedness
- Nausea
- Unusual fatigue or weakness
- Muscle cramping
- Rapid breathing or elevated heart rate
- Confusion
These are common signs of heat exhaustion, which occurs when your body struggles to balance fluid levels and temperature. Acting quickly can prevent progression to more serious heat illness.
It’s important to understand that exertional heat illness can build up over consecutive days of exercise. If you’re not giving your body enough recovery time or rehydrating enough on a very hot day, you can increase your risk for heat-related illness the next day. Sleep deprivation can also compound these effects, so make sure your training includes adequate sleep.
If you’re wondering if you’re dehydrated, Dr. Fox says daily weight monitoring is an easy way to check. Because most sudden weight changes are due to water loss or gain, rapid drops can indicate dehydration. Athletes should be within one percent of the previous day’s weight before starting the next training session.
Finish strong
Adjusting or cutting a run short due to the heat isn’t a setback—it’s smart, responsible training. Building flexibility into your plan helps you stay consistent over time, which ultimately matters more than any single workout.
By incorporating these strategies—smart scheduling, proper hydration, weather awareness, and listening to your body—you can train safely through the summer and arrive at race day strong, confident, and ready to perform.
Need more personalized tips? Find an SSM Health sports medicine practitioner.
