Dear Doctors: I don't enjoy exercise, but it's important for your health, so I do it. We've had really humid weather, and I'm having trouble staying active. I run and, in this weather, I just can't go as far or as fast. My roommates are teasing me and say it's all in my head. Are they right?
Dear Reader: First, congratulations on your commitment to staying active. You're investing in both your current and your future good health. Regular exercise benefits not only the body, but the mind as well. Staying active bolsters cardiovascular health, helps with blood sugar control and helps maintain bone strength. It supports mobility, flexibility and balance, and it aids in weight management. Regular exercise can also improve mood, contribute to high-quality sleep and is associated with a lower risk of cognitive decline.
We're glad we can reassure you that no, your struggles to exercise in high humidity are not all in your head. That moisture-laden air has a real and measurable effect on physical performance. Marathon race data show that hot and humid weather conditions can slow a runner's performance by up to 5%. It may not sound like much, but for someone running a marathon, that adds about 10 minutes to their finish time.
Muscle movement generates heat. When it's enough to raise core body temperature, the body takes steps to cool itself off. It sends blood to the surface of the skin. This prompts the sweat glands to produce perspiration. In dry conditions, the evaporative effect carries heat away from the body. But high humidity derails the process. Because the air already contains moisture, sweat evaporates more slowly. The higher the humidity, the lower the cooling.
Maintaining core temperature is crucial, so your body does not give up. Trying to shed heat, it sends even more blood to the blood vessels near the surface of the skin. Your heart rate goes up and your lungs work harder. With less blood flowing to working muscles, the oxygen and nutrients it would deliver are in shorter supply. The end result is the fatigue that can make exercising in humidity feel like a literal uphill climb.
You can't control the weather, but you can adapt to it. Slow down, shorten your distance and pay attention to how you feel. Rather than distance, let your goal become continuity. Run in the coolest part of the day. Wear lightweight, light-colored and breathable clothes. And be sure to pay close attention to hydration.
Believe it or not, your body adapts with each muggy run. Sweating begins sooner and becomes more copious. The sweat itself changes and gets more diluted. Your body's blood volume increases. This allows the workload of the heart to decrease. As these changes take place, core body temperature begins to rise more slowly. Our bodies gradually acclimate to heat and humidity. In as little as two weeks, you may find that exercise begins to feel easier again.
(Send your questions to [email protected], or write: Ask the Doctors, c/o UCLA Health Sciences Media Relations, 10960 Wilshire Blvd., Suite 1955, Los Angeles, CA, 90024. Owing to the volume of mail, personal replies cannot be provided.)
