Physical exercise is increasingly being advocated as a means to maintain and enhance good mental health. In general, findings from research indicate that exercise is associated with improvements in mental health including mood state and self-esteem, although a causal link has not been established. Research on acute exercise indicates that 20 to 40 minutes of aerobic activity results in improvements in state anxiety and mood that persist for several hours. These transitory changes in mood occur in both individuals with normal or elevated levels of anxiety, but appear to be limited to aerobic forms of exercise.