"266 contact. Walking for exercise, gardening or yard work, bicycling or exercise cycling, dan cing, swimming, and golf are activities with the lowest injury rates. In the amounts commonly done by adults, walking (a moderate – intensity and low - impact activity) has a third or less of the injury risk of running (a vigorous - intensity and higher impact a ctivity). The risk of injury for a type of physical activity can also differ according to the purpose of the activity. For example, recreational bicycling or bicycling for transportation leads to fewer injuries than training for and competing in bicycle r aces. People who have had a past injury are at risk of injuring that body part again. The risk of injury can be reduced by performing appropriate amounts of activity and setting appropriate personal goals. Performing a variety of different physical activit ies may also reduce the risk of overuse injury. The risk of injury to bones, muscles, and joints is directly related to the gap between a person’s usual level of activity and a new level of activity. Increase Physical Activity Gradually Over Time Scientif ic studies indicate that the risk of injury to bones, muscles, and joints is directly related to the gap between a person’s usual level of activity and a new level of activity. The size of this gap is called the amount of overload. Creating a small overloa d and waiting for the body to adapt and recover reduces the risk of injury. When amounts of physical activity need to be increased to meet the Guidelines or personal goals, physical activity should be increased gradually over time, no matter what the perso n’s current level of physical activity. Scientists have not established a standard for how to gradually increase physical activity over time. The following recommendations give general guidance for inactive people and those with low levels of physical acti vity on how to increase physical activity: • Use relative intensity (intensity of the activity relative to a person’s fitness) to guide the level of effort for aerobic activity. • Generally, start with relatively moderate - intensity aerobic activity. Avoid relatively vigorous - intensity activity, such as shoveling snow or running. Adults with a low level of fitness may need to start with light activity, or a mix of light - to moderate - intensity activity. • First, increase the number of minutes per session (durat ion), and the number of days per week (frequency) of moderate - intensity activity. Later, if desired, increase the intensity. • Pay attention to the relative size of the increase in physical activity each week, as this is related to injury risk. For example, a 20 - minute increase each week is safer for a person who does 200 minutes a week of walking (a 10 percent increase), than for a person who does 40 minutes a week (a 50 percent increase). The available scientific evidence suggests that adding a small and c omfortable amount of light - to moderate – intensity activity, such as 5 to 15 minutes of walking per session, 2 to 3 times a week, to one’s usual activities has a low risk of musculoskeletal injury and no known risk of severe cardiac events. Because this ran ge is rather wide, people should consider three factors in individualizing their rate of increase: age, level of fitness, and prior experience. The amount of time required to adapt to a new level of activity probably"