It is important to start your activity sessions with a warm-up period for 2 to 5 minutes. The purpose of a warm-up is to get your cardiovascular system and muscles ready to do the more strenuous activity. Doing a warm-up will help you avoid muscle injury. Warm-up activities include fast walking, jogging in place, skipping rope or cycling on a stationery bicycle. These are considered "big muscle" activities because they use the big muscles in the legs and arms. Warm-up activities should be done in a smooth, continuous way.