Take a really steamy bath
A recent study found that sitting in a 105 degree Fahrenheit imagine just below scalding bathtub after a treadmill workout six days in a row helped athletes slice time off a 5-K. The superhot water trains your body to deal with heat in real time.
Wearing layers during your gym workouts or when it's mild outside say, low 70s, also teaches your body to embrace a higher core temperature, which you'll face outdoors. Pile on enough so that you're sweaty within five to 10 minutes of your workout, then call it quits after 30 minutes. Stop is you feel dizzy or your heart is racing.
Hang out in the steam room
The moisture helps adjust your body to humidity. The H word can doubly kill your energy because it causes you to lose more water via sweat. Training in a dry climate? Hit the sauna for dry heat.