Physical activity is good for your health, but it can stress and strain your body if not done right. If it's done too suddenly or without basic precautions, exercise can lead to injury or illness.

Even if you have long been active and are fit, keep safety in mind. Do not assume that basic precautions do not apply to you.

The most important ways to avoid injury and illness are to:

• Learn about the risks of any new activity you begin. Take lessons, if appropriate.
• Wear clothing that is right for your activity, including shoes that have good support for your feet.
• Always use the safety gear that is recommended for your chosen activity, such as helmets and knee pads. Learn about the use and proper fit of safety equipment.
• Begin an exercise routine slowly and gradually increase intensity.
• Pay attention to your body's signals, such as pain and fatigue, when starting a new activity or when increasing the intensity of your physical activity. General muscle soreness is common when you try a new activity, but pain can mean you're injured. If you are very tired, you may be doing too much too soon.

Some injuries and illnesses related to physical activity include the following:

• Dehydration may result from losing too much water through sweating and failing to replace it by drinking as you exercise. Follow these guidelines for avoiding dehydration when exercising.
• Heat exhaustion, heatstroke, or dehydration may result from exercising in heat and humidity. Review these guidelines for exercising in hot and humid weather.
• Overhydration (hyponatremia) is having too much fluid in the body. It's possible to become overhydrated from drinking too much fluid. This is rare, but it can happen to people who do strenuous exercise for a long time, such as long-distance runners. You can avoid overhydration by learning to match your fluid intake to how much fluid you lose through sweat, and by noticing if you have symptoms of overhydration. Symptoms can include feeling bloated (your watch band or race bracelet may become tight), sick to your stomach, or confused. Overhydration during exercise is unusual, but it is a medical emergency when it happens.⁸
• Overuse injuries can happen to anyone who overuses certain joints or muscles. Doing too much too soon or intensive exercise and sports can lead to overuse injuries. Not using the proper form for the activity or wearing poorly fitting shoes can also cause injury.
• Exercise-induced asthma can occur regardless of whether you have asthma at any other time.
• Overtraining can cause fatigue and irritability as well as increased risk for injury and illness.
• Heart attack is rare, but you should be aware of its symptoms.