The number of older Americans will double in the next 4 decades to nearly 90 million, placing an unprecedented financial and resource burden on the health care system. Exercise has clear and demonstrable physical benefits, but a more precise understanding of how exercise supports cognitive function is essential. Demonstrating definitively that exercise as recommended by public health entities has benefits for cognition would have enormous public health implications, encourage the public to adapt more active lifestyles, and stimulate the development of effective exercise delivery programs.

Older adults often experience physical decline that can be directly ameliorated by physical activity and exercise. Evidence is building that exercise prevents cognitive decline or delays the onset of debilitating dementia (e.g. Alzheimer's disease) yet, the optimal dose and combination of exercise modalities for promoting brain health, however, remains unknown and essentially untested.

The long-term research goal of this project is to develop and test strategies to support successful aging and prevent Alzheimer's disease. The study will enroll 280 individuals, age 65 to 80 years without cognitive impairment, into a 26-week exercise intervention to test the combined and independent effects of aerobic and resistance training on cognition, brain structure, and physical function. The project will also explore underlying biological mechanisms that may link exercise with brain health.

Participants will be randomized into 1 of 4 groups: flexibility, toning and balance (control), aerobic exercise training, progressive resistance training, or combined aerobic and resistance training. All intervention groups represent the most common modalities of exercise and directly reflect the public health recommendations for aerobic and resistance training. Exercise training will occur in a community setting through the network of Greater Kansas City Young Men's Christian Association. It is hypothesized that 26 weeks of exercise will improve 1) cognitive performance, 2) regional brain volume, 3) cardiorespiratory fitness and strength 4) biomarkers.

This will be the largest study to assess the combined and independent effects of the two most recommended forms of exercise. Demonstrating specific exercise effects on cognitive function and brain health in older adults would have enormous public health implications. The study's results will also impact public health policy and education by providing evidence towards the specific or synergistic effects of aerobic and resistance training on cognition and brain structure. Encouraging the public to adapt more active lifestyles and stimulate the development of effective exercise delivery programs to enhance initiation and maintenance of physical activity interventions is key to increasing the number of quality years of life for America's aging population.

Inclusion Criteria:

• Age 65-80 yrs (inclusive at time of consent).
• Conversant English speaking and reading ability.
• Medical clearance by a health care provider.
• Reliable means of transportation.
• Telephone Interview of Cognitive Status score > 25 and adjudication of normal cognition based on cognitive test data by a study medical monitor.

Exclusion Criteria:

• Intention to move out of the area or travel for more than 4 weeks in the next year.
• Use of an assistive device for ambulation.
• Joint pain severe enough to prevent taking walks in community, lifting objects over your head due to pain or restriction of movement, or that is worsened by increasing physical activity.
• Any MRI contraindications or refusal to attempt MRI.
• Treatment for alcohol or substance abuse in the last 2 years.
• Treatment for cancer (other than non-metastatic, localized cancer) in the last 2 years.
• Currently taking insulin.
• Diagnosis of heart disease, heart failure, heart attack, or heart surgery or chest pain with effort in the last 2 years.
• Untreated atrial fibrillation, valve replacements, angioplasty or stent placement in the last 2 years regardless of physician clearance.
• History of major psychiatric illness including schizophrenia (not including general anxiety disorder or depression), multiple sclerosis, Parkinson's, Dementia, mild cognitive impairment, brain injury (traumatic or clinically evident Stroke), or similar, likely to negatively impact cognitive testing.
• Head injury with loss of consciousness for more than a few minutes.
• Change in blood pressure medication in the last 2 months.
• Considered "Active" or engaging in a progressive resistance training 2 or more times a week.
• reported condition likely to compromise ability to safely perform exercise as determined by study medical monitor (e.g. chronic obstructive pulmonary disease, Lupus, end stage renal disease, etc.)

All data generated during the project will be entered into a secure database. This database will be housed on a secure network drive that is routinely backed-up to an offsite data storage location. Upon completion of the project, all data will be de-identified and available for other investigators at their request, in compliance with the NIH guidelines. It is not anticipated that unique resources will be developed and thus a plan for resource sharing is not provided.

Raters (psychometrician, exercise physiologist) who perform outcome assessments will be blinded to the participant's intervention group. The study medical monitor and investigators will be unblinded to assist with safety assessments and address safety concerns or adverse events.