If the temperature starts to rise, and you're sweating quite a bit, then have some salty foods. If you have high blood pressure speak with your doctor first. After an hour of activity, you need to start replenishing your carbohydrates (glycogen), but also essential electrolytes, like sodium. Foods like pretzels, chips, crackers, salt tabs and some bars will have enough sodium and carbohydrates to provide your body with the amounts needed to get you through the activity.
More: 6 Best Hydrating Foods for Athletes
Urine Color Levels
You always want to start your morning with a clear to light yellow urine color. This means you're properly hydrated prior to your race or sporting event. If your urine color is a dark yellow or even sort of brownish, then you are not properly hydrated and you need to start drinking fluids before you get out there in the heat. You want to start off on a positive note, and this is one way of doing that.
More: What Your Urine Says About Your Health
Practice Ahead of Time
If your sporting event is out of town, try to go at least a week in advance to that destination so your body can start to adjust to the temperature conditions. If that's not possible, then during your training schedule, try to find days that will be similar to the event and practice that day with the proper clothing, hydration and your food requirements. This will give you an idea on what you need to improve on or how your body will react under these conditions.
When you're done with either your practice or event, make sure you take time to cool down. Even in those hot temperatures, walk around (don't sit) to make sure you re-circulate the blood throughout your body. You can go inside to a cooler room to cool off, but don't sit—keep moving. There's a lot of blood in your legs from the activity you just did (blood pooling), so if you don't cool down properly and get the blood to all the necessary parts of your body, you will get dizzy, nauseous, and possibly pass out and injure yourself in the process. Spend at least 15 to 20 minutes drinking fluids, eating small snacks, and cooling down before you sit.
More: Importance of Cool Down
Many people will bonk or their bodies will just give out during these hot and humid conditions because they fail to prepare and plan. You set yourself up for success when you plan ahead of time. Practice and prepare so you're aware of the dangers that go with exercising in hot temperatures. If you're running a race where the conditions are just horrible because of high temperatures and humidity, there will be a lot of medical attention available. But, listen to your body and make sure you're drinking enough fluids, staying cool and eating the correct foods.
Find a fitness class.