GYM exercise, even after age 50, can add healthy and active years to one's life. Studies continue to show that it is never too late to start exercising and that even small improvements in physical fitness can significantly lower the risk of death. Simply walking regularly can prolong life in the elderly. Moderately fit people, even if they smoke or have high blood pressure, have a lower mortality rate than the least fit. Resistance training is important for the elderly, because it is the only form of exercise that can slow and even reverse the decline in muscle mass, bone density, and strength. Adding workouts that focus on speed and agility may be even more protective for older people. Flexibility exercises help reduce the stiffness and loss of balance that accompanies aging. Inactivity is one of the four major risk factors for heart disease, on par with smoking, unhealthy cholesterol, and even high blood pressure. Like all muscles, the heart becomes stronger and larger as a result of exercise so it can pump more blood through the body with every beat. Exercise does not increase the maximum heart rate, but a fit heart can pump more blood at this maximum level and can sustain it longer with less strain. The resting heart rate of those who exercise is also slower, because less effort is needed to pump blood. For preventing heart disease frequency of exercises may be more important than duration. Exercise even helps reverse some of the effects of smoking. Children should be especially encouraged to exercise every day to prevent heart disease later in life.