Recent studies have shown the encouraging effects of fitness training on human cognition, and brain structure and function. Such effects are of great interest both for what may they tell us about the nature of cognitive and brain aging and also for their public health implications. This study will test the hypotheses that: 1) improvements in aerobic fitness of older adults will lead to improved performance on a variety of cognitive processes, and especially those processes that are supported by frontal regions of the brain; 2) improvements in cognitive processes due to enhanced aerobic fitness will be visible on fMRI scans, and will be similar to those of young adults; 3) improvements in aerobic fitness, over the course of a 1 year intervention, will result in increases in gray and white matter volume.

One hundred forty sedentary older adults will be recruited for this study. Participants will be randomized to an aerobic exercise intervention group, or to a stretching and toning control group. Aerobic exercise sessions will be conducted three times a week for one year, beginning at a light to moderate intensity level over the first two months and progressing to a moderate to high level for the remainder of the year. The control group will meet on the same basis as the intervention group, and will participate in an organized program of stretching, limbering, and toning for the whole body that is specially designed for individuals 60 years of age and older.

During this time, participants will exercise, keep a daily exercise log detailing distance walked (routes will be measured and mapped for participants), time spent in aerobic activity, degree of intensity (rating of perceived exertion), general level of affect during exercise, resting and exercise heart rates. Participants will participate in the MRI/fMRI, physiological (cardiorespiratory) and psychosocial testing prior to the beginning of the fitness training intervention, following 6 months of fitness training, and at the conclusion of the 1 year of fitness training.

Inclusion Criteria:

• 60 to 75 years of age (for Sedentary Older Adults)

• Sedentary Older Adults: no physical activity in last six months; Young Comparison Sample: Moderately active lifestyle

• Capable of performing exercise

• Personal physician’s examination and consent to participate in testing and exercise or control intervention

• Successful completion of graded exercise test without evidence of cardiac abnormalities or responses

• Adequate performance on the Pfeiffer (1979) Mental Status measure - Corrected (near and far) vision 20/40 or better

• Right-handed

• Intention to remain in the local area over the study period

Exclusion Criteria:

• Sedentary Older Adults: self reported physical activity on regular basis (2 times or more per week) in last six months; Young Comparison Sample: sedentary or highly active/athletic lifestyle

• Any physical disability that prohibits mobility (walking), stretching etc.

• Depression score on GDS indicative of clinical depression

• Presence of any implanted devices such as cardiac pacemakers or autodefibrillators; neural pacemakers, aneurysm clips in the CNS; cochlear implants; metallic bodies in the eye or CNS; any form of wires or metal devices that concentrate radiofrequency fields

• Left-handed

• Individuals with chronic inflammation (e.g. severe arthritis, psoriasis, inflammatory bowel disease, asthma, polyneuropathies, Lupus)

• Intent to move or take an extended vacation (i.e. longer than 1 month during the study period)