Exercising outdoors is usually a fun way to get in shape, but you need to make sure you don’t expose yourself to undue risk when the weather gets hot. But when exactly is it warm enough to worry about the safety of exercising outdoors?

Humidity actually plays a vital role here. If you’re not used to the conditions, high humidity can make even temperatures of 70 degrees dangerous. When you’re dealing with both heat and humidity, your sweat does not evaporate the way it’s supposed to. Gauging the combination of heat and humidity is not a natural instinct, and many people don’t recognize dangerous conditions until it’s too late.

A hard workout creates heat in the muscles being exercised. If that heat can’t be efficiently carried to the extremities and dumped into the surrounding atmosphere, it will stay inside the body. The result is a dangerous spike in core temperature that can lead to organ damage and other severe injuries. Exercising in extremely hot conditions is not something you can make safe with willpower or endurance. The issues are the immutable rules of physics and physiology.

Heat illness has some common symptoms to watch out for. These include headaches, nausea, vomiting, weakness, and altered mental states. (Examples of the latter phenomenon would be incoherent speech, confusion, or aggression.) Internal temperatures can reach levels of 105 or even 114 degrees when the body’s sweating mechanism shuts down. Without the cooling it vitally needs, the body will eventually start to cook. This is where heat stroke begins. If it is not treated and relieved, it can be fatal.

Working out tends to add significantly to the stress that causes heat injuries. When you experience exercise exhaustion in an outdoor workout, the factor pushing you over the edge is certain to be the exercise rather than the weather.

Stay Hydrated

Hot-weather exercise will bring up your body temperature. The body has a built-in cooling mechanism in the form of perspiration, but there are limits to how much heat it can carry away. Under the influence of sustained high temperatures, heat exhaustion or even heat stroke can set in.

It’s not a good idea to prepare for a hot weather exercise session with calorie-packed juices or sports drinks. Water is the safer hydration option when the temperatures are high.

Hydration is absolutely essential to keep your body’s cooling system in order. During even moderate physical activity in hot weather, you can lose up to three percent of the water in your body to perspiration. Make sure you drink copiously to replace that lost moisture.

One good way to keep yourself hydrated during high-temperature workouts is to eat electrolyte-rich snacks during breaks. Small pieces of fruit (e.g. oranges and apples) or water-rich vegetables (carrots or celery sticks) will make it easier to stay hydrated.

How Much Water Is Enough?

Your body has a handy mechanism for letting you know whether or not you’re properly hydrated. Check the color of your urine when you engage in hot weather exercise. You want to keep it clear or light yellow, roughly the shade of lemonade. If your urine starts coming out darker, up your water intake.

Note that there are certain forms of medication that alter the color of your urine, so this hydration check is not always foolproof. As a good general rule, make sure you’re taking in eight to 10 ounces of water every 20 minutes while you’re exercising.

The Danger Of Overhydration

Unfortunately, there is such a thing as too much water, even on the hottest of days. Over-hydrating leads to low blood sodium, a condition known as hyponatremia. Drink only when you’re thirsty when you’re not being active. When you are engaging in strenuous exercise, increase your intake.

Avoid sports drinks in order to steer clear of excess calories. The amount of nutrition they supply is far in excess of your needs if you’re also using them to fulfill all your hydration requirements.

Remember that sports drinks are designed for professional athletes who engage in high-intensity training for very long periods. Even if you are very fit and working out for long periods, you may need to water down sports drinks to keep their calorie counts healthy.

As suggested above, you can get the spare electrolytes you need by having a modest snack of fruits or vegetables during an extended workout.

Pace Yourself

If you’re not used to exercising in hot temperatures, ease up on your workout plans at the start. You’re not going to be capable of doing as much or moving as quickly as normal. Even if you can complete a four-mile run on the beach in Los Angeles without a strain, a half-mile stroll in New York with high humidity and 103-degree temperatures will feel a lot different.

Substitute lower-intensity exercises while you’re acclimating to the climate. If you run, try jogging instead. If your preferred exercise is walking, take your pace down slower. You can increase the intensity and duration of workouts slowly as your body gets used to the heat. Note that it’s an excellent idea to discuss high-temperature exercise with your doctor if you have any long-term medical concerns or take prescription drugs.

Don’t Work Out In The Hottest Hours

Schedule your workouts as early or as late as possible (first thing in the morning or near dusk) to avoid the hottest hours of the day. If the hot midday hours are the only time you can work out, try hitting the pool for some aqua-aerobics.

Dress In Lightweight Clothing And Light Colors

Darker clothes absorb heat and that energy can end up transferring to your body. Wear the loosest, lightest clothes (both in terms of color and weight) you feel comfortable with. The more air you can get over your skin, the easier it will be to get rid of unwanted heat.

Eat With An Eye Toward Your Energy Levels

Summer workouts are an excellent time to bring out your juiciest snacks. Fruit is ideal; dry and salty snacks (crackers, nuts, energy bars) should be avoided. Note that these dry snacks are also frequently too calorie-dense to line up with your weight-loss goals.

Don’t Push Yourself Too Far

If you think cutting your four-mile run short is going to feel bad, let us assure you it’s not nearly as nasty as a case of sunstroke. Listen to what your body tells you. You may need to call 911 if you experience the any of the following symptoms:

• Lightheadedness
• Weakness
• Headache
• Dizziness
• Pale skin
• Nausea/Vomiting
• Rapid Heartbeat
• Muscle Cramps

If you do have to call 911, get to a shady area, take off any excess clothing and use anything that may be available to cool down. If you are able to get indoors, a cold shower or even ice packs may help.

Just remind yourself that even a brief workout is good for your body and it is getting exercise on a regular schedule that matters the most. If you’re working out every day, it’s perfectly alright to cut a session short.

When temperatures rise over 90 degrees, work out indoors rather than outdoors.