How to train safely in the heat and humidity of Puerto Rico

In Puerto Rico it is hot almost all year, and the humidity makes it feel worse. You can train well, but you have to adjust the time, your hydration and the intensity, especially in summer.

Short answer: train early in the morning or late in the afternoon, drink water before, during and after, wear light-colored, lightweight clothes, and during the first days of strong heat lower the intensity. Stop right away if you feel dizzy, get a headache or feel nauseous, and call 911 if there is confusion or fainting.

Why does humidity make the heat feel worse?

Your body cools down when sweat evaporates from your skin. With high humidity, sweat barely evaporates: you sweat a lot but cool down little. That is why the heat index (what you feel with the humidity) can be several degrees higher than the thermometer reading. For example, at 90 °F (32 °C) and 70% humidity, the heat index is about 106 °F (41 °C).

The U.S. National Weather Service (NWS) uses these risk levels for people who spend a long time in the heat or exercise:

How much water should I drink when training in the heat?

• Before: arrive hydrated. Drink water through the day and a glass or two in the hours before training.
• During: take sips every 15 or 20 minutes, without waiting to be very thirsty.
• After: weigh yourself before and after training. For every pound you lost, drink about 20 to 24 ounces of fluid over the next hours.
• Electrolytes: if you train for more than an hour or sweat a lot, a drink with electrolytes or a meal with some salt helps replace what you lost.

Tip: check the color of your urine. If it is light, you are doing fine; if it is dark, you need more water.

What is the best time to train?

• The best times are early in the morning or after the sun goes down. Avoid the strong midday sun.
• If you train at home, open the windows, use a fan or the air conditioning. Training online has that advantage: you choose the coolest spot.
• If you run or walk outside, look for shade or the beach early in the day.

How long does the body take to get used to the heat?

Your body takes 1 to 2 weeks to adapt to the heat. If you are back from a trip, just starting to train or a heat wave arrives, keep the first sessions shorter and easier, with more rest, and build up.

What should I wear to train in the heat?

• Light-colored, lightweight, breathable clothes.
• A cap and sunscreen if you are outdoors.
• Be careful if you take medication or have a heart or blood pressure condition: ask your doctor how the heat affects you.

When should I stop?

• Heat exhaustion: heavy sweating, cool and clammy skin, dizziness, headache, nausea, cramps or extreme tiredness. Stop, move to the shade or a cool place, drink water and cool off. If you do not feel better within an hour, get medical help.
• Heat stroke (emergency): confusion, slurred speech, fainting, very hot skin or seizures. Call 911 and cool the person down with cold water while help arrives.

Want to start at home, in a cool spot? Try the 20-minute no-equipment workout or see how many days a week to train.

Sources

• Sawka M. N. et al. (2007). American College of Sports Medicine position stand: Exercise and fluid replacement. Medicine & Science in Sports & Exercise, 39(2):377-390. doi.org/10.1249/mss.0b013e31802ca597
• U.S. National Weather Service (NWS). Heat Safety and the heat index. weather.gov/safety/heat and weather.gov/ama/heatindex
• Centers for Disease Control and Prevention (CDC). Heat and Health. cdc.gov/heat-health