To reduce the risk of injuries and other adverse events while being physically active, people should choose to do types of physical activity that are appropriate for their current fitness level and health goals. Some activities are safer than others. If you have never run a mile, it’s not time to sign up to run a marathon.
Increase your hysical activity gradually over time intensifying how often and how long activities are done. Start walking 1 mile, 3 days a week, then 2 miles, 5 days a week, etc. Protect yourself by using appropriate gear and sports equipment, looking for safe environments, following rules and policies, and making sensible choices. For example, while riding a bike, a helmet should be worn and high traffic areas should be avoided.
Be under the care of a health-care provider if they have chronic conditions or symptoms. Your provider will determine the types and amounts of activity appropriate for you. For instance, there are concerns with those who have aggravating arthritis pain and causing further joint damage, and knowing which types and amounts of activity are safe for their joints.
Source: 2008 Physical Activity Guidelines for Americans