If possible, take part in outdoor activities and even strenuous indoor tasks in the morning hours or postpone them until evening when temperatures are cooler. If you must work outdoors, stay hydrated. Wear lightweight, loose-fitting clothes and stay out of direct sunlight as much as possible. Take frequent breaks, and replace the salt and minerals you're losing through perspiration by drinking sports beverages.
Just because you're young and healthy doesn't mean you're immune to the effects of the heat. If you experience muscle spasms, abdominal pain or pain in the arms or legs, stop what you're doing. Relax for a while in a cool spot and drink plenty of liquids. You may be suffering from heat cramps. If the symptoms persist longer than an hour, seek medical attention. Either way, stop working outdoors for the day.
If you experience dizziness, confusion, fainting, excessive sweating, nausea, a rapid pulse, headache or your skin is hot but you've stopped sweating, you may be suffering from heat exhaustion or possibly even heat stroke. Both are more serious than heat cramps. Stop what you're doing immediately. If your body temperature is over 103 degrees F, seek medical attention as soon as possible. Heat exhaustion can lead to heat stroke, and heat stroke can be fatal. These are serious symptoms, so pay attention to what your body is telling you.