When the air conditioning broke down, the average temperature rose to 78 degrees. It didn't seem like much, but what happened to people working in that environment was amazing. At 75 degrees, people who were clothed start becoming more lethargic and sleepy. People in gym shorts and a workout shirt didn't much notice, but anyone wearing long pants and a long-sleeve shirt started to feel warm.
At 78 degrees, people had to stop much more frequently, cold water consumption rose dramatically and we started using chilled towels during the workouts instead of just at the end. When we looked at the research, if temperature rose just two more degrees to 80, we could expect the effectiveness of the workouts to drop by as much as 40-50%!
Now here's the really odd part. Some of the people who weighed themselves after a session in the heat saw their weight drop by as much as 1 to 1.5 pounds. Yet they hadn't been able to lift as much or run as far. What was going on? Was the heat helping their bodies burn more fat?
No, the heat just made them sweat more. The weight loss was all dehydration that they put right back on the moment they drank some water. They didn't drop a pound of fat, just fluid. What's worse is that because they didn't exercise at their full capacity, they didn't burn as much fat or build as much muscle as they would have in a cooler environment. The long-term benefit of their exercise was reduced.
For a couple of days, it really makes no difference in long-term health. But if you're constantly working out in a hotter environment, your workouts may be 50% less effective. Over time that number is dramatic.
That doesn't mean everyone should workout in 72 degree temperature. In fact, the ideal number changes depending on the type of workout you're doing. According to OSHA (The Occupational Safety & Health Administration) cardio is best at about 68 degrees. The International Fitness Association recommends that when doing yoga the temperature should be kept at about 80.
Competitions held in extreme environments are also different. If you plan on running a marathon in Death Valley, you should be training in temperatures that more closely match what you'll experience during the race. The same is true if you're entering a cold weather competition.
For half your workouts, get used to the clothing and environment you'll experience during the race so you'll know what to expect when hit with the temperature extremes. The rest of the time, exercise in the appropriate temperature range for your workout type.
The next time you workout, check the thermostat. If you're doing cardio or weight training it should be between 68 and 72 degrees Fahrenheit. For yoga expect it to be a warmer 80.