Prosocial Behavior and Exercise Among Older Adults

Inclusion Criteria: * Between 55 and 80 years of age * Physically underactive (moderate or vigorous physical activity for less than 2 days per week for the preceding 3 months) * No evidence of any major psychological illness * Written permission from the participant's primary care physician with specific certification of no severe risk of cardiovascular disease * Participant resides within a 35-mile radius of the study site * Participant will remain in the area for the duration of the study Exclusion Criteria: * Self-reported evidence of cardiovascular disease risk, or documentation by the primary care physician of at least one of the following within the past 5 years: * Myocardial infarction (MI) * Percutaneous transluminal coronary angioplasty (PTCA) * Chronic or unstable angina at rest or during physical exertion * New York Heart Association (NYHA) Type I through Type IV congestive heart failure * Unstable ventricular arrhythmias * Cardiovascular surgery (coronary artery or valvular heart disease) * Ischemic or hemorrhagic stroke * Intermittent claudication during physical activity * Edema in feet * Self-reported or documented evidence of rheumatoid arthritis * Self-reported or physician-reported evidence of current cigarette or cigar smoking * Self-reported treatment for psychiatric illness within the past 5 years: * Treatment for major depression or schizophrenia * Currently receiving lithium or neuroleptics * Hospitalization with the last 5 years for depression, or clinical judgment of treatment for major depression * Hearing or sight impairments * Cognitive impairment * Alcohol consumption greater than 21 drinks per week, or self-reported alcoholism * Inability to speak or read English * Judgment of clinical staff * Current participation in another medical intervention study