The mercury is rising, and temperatures are pushing into the 90-plus-degree range. Summer is in swing and a little heat ought not slow our active population down. Heat exhaustion, dehydration, and the discomfort of physical activity in the heat can, so read on and avoid being waylaid this season.

The body is an efficient cooler; humans have "breathable" skin with little hair, and a respiratory system not many other mammals have. It appears that humans are designed to be active in hot temps and avoid cold temps. Once the body begins moving, the byproduct of energy expenditure is heat. The heat is dissipated through the skin, and perspiration keeps the skin cool.

But this system can only handle so much before the body will self-regulate by causing nausea and exhaustion symptoms - prompting the body to slow down.

These symptoms can be managed with proper hydration. It would be easy to write "just drink more water" but that isn't always true. When you perspire, you excrete minerals as well as fluids. Sodium, mainly, needs to be replenished. Is the drink you are drinking absorbed readily? Osmolality is important to consider: Once liquid is in the stomach, it is either hypo or hypertonic. This means that it requires additional fluid to balance the proportions of sodium or sugar in the drink to that of the body. A very dense sports drink is hypertonic, meaning that water will be taken out of the body and into the gut in order to process the liquid.

It's easy to see how this is a problem.

Examples of hypertonic solutions: juice, soda, sports drinks (at regular density), beer. Hypotonic solutions: half-strength sports drinks, water with sea salt, coconut water (unsweetened), low calorie sports drinks. It's also important to consider gels and bars which can produce the same symptoms. A bar that's oats, chocolate, and nuts will take a lot to digest the carbohydrate and will zap any means of hydrating. On a hot day, stick to light drinks and drink plenty - a good idea is 8 ounces every 20 minutes of activity.

Heat exhaustion is another concern. This is when the body cannot cool itself as needed in the heat. Usually nausea, headache, dizziness, shortness of breath and higher-than-average heart rate show heat exhaustion. If it's ignored, the body will fall into a heat stroke. This is where the body will stop sweating, in order to keep fluids. Delirium, confusion, irritability are commonly observed. It's important to cool the body off if overheated, as heat stroke can lead to serious medical emergencies, such as heart attacks and other complications.

Avoid this by keeping cool - both literally and figuratively. Sometimes if it's too hot, exercise intensity ought to be scaled back. Also, keeping the sun off the skin is effective; this could be accomplished with loose sleeves or light pants. A hat with a brim will also keep the sun at bay. Of course, use cold beverages to cool the internal temperature. A frozen towel, ice pack, or other measure can also be handy.

The symptoms of heat exhaustion are very similar to general fatigue. Don't let heat exhaustion slow down activity and pleasure outdoors this summer. Combat with proper hydration and replenishment. Use cooling techniques, and scale back according to conditions.