There are essentially four different categories of exercise, and, according to the National Institute on Aging (NIA), participation in all four types is necessary for full health benefits: endurance / aerobics, strength training / weight lifting, balance, and stretching / flexibility.
The NIA states that strength-training / weight-lifting exercises should be performed two to three days per week with a rest day between sessions. Strength training activities should include exercises for all major muscle groups – shoulders, arms, chest, abdomen, back, hips, and legs.