Aerobics is a form of exercise that comprises rhythmic aerobic exercise with stretching and strength training components in order to improve all elements of fitness (flexibility, muscle strength, and cardio-vascular fitness). It is typically performed to music in a group setting with a leader, although it can be practiced solo and without musical accompaniment. Physical Illness being targeted, practitioners go through variable routines comprising a number of different exercises. Proponents of aerobics cite staving off boredom and working out the whole body as two of the advantages of aerobics over other types of exercise. The reputedly higher safety factor inherent in a fitness routine led and overseen by a trained professional is another.