Effects of Exercise Intervention on Aging-related Motor Decline

The U.S. Census reports over 14 million U.S. Veterans (>63%) are beyond mid-life (>55 years). Declines in upper extremity motor performance respective of strength and dexterity are well documented within this age cohort). Recent cross-sectional research has discovered that aging related motor deficits may be influenced by a loss of interhemispheric inhibition (IHI) between primary motor cortices. However, this loss may not be an inevitable consequence of aging. Work from previous VA OAA Predoctoral and CDA-1 awards have shown that aerobic fitness may serve to mitigate losses in interhemispheric inhibition assessed by both functional magnetic resonance imaging (fMRI) and transcranial magnetic stimulation (TMS). That is, individuals who are aerobically fit show higher levels of IHI and improved dexterity and reaction times.

In light of new evidence from the investigators' lab's recent cross-sectional studies, physical activity over the long term (at least 2-5 years) may serve to alter levels of IHI and improve motor performance in the upper extremity. Aerobic exercise may provide a mechanism (reduced loss of interhemispheric inhibition) that could serve to improve motor function, but the neural mechanism responsible for such effects remains unclear. Previous investigations of interhemispheric communication and exercise have been limited by nature of inquiry, as cross-sectional research cannot measure changes over time in participants. As such, it is currently unknown how exercise may directly affect levels of interhemispheric communication and motor performance.

Behavioral interventions (motor strength and coordination) have been shown to be effective in improving upper extremity motor performance in older adults, however the duration of these gains appear to be short-lived. After as little as a few weeks of detraining, motor strength and coordination in the upper extremity rapidly begins to return to pre-intervention levels. Evidence from exercise interventions assessing gait and locomotion have shown that exercise programs over a longer term (>6 months) are associated with improved proprioception, fewer falls and better balance. However, the comparison of outcomes of upper extremity function in elderly adults respective of exercise duration remains largely unexplored. In addition to comparing the effects of short-term exercise (3 months) versus behavioral training (3 months) on upper extremity function, the current proposal will evaluate if a longer-term (6 months) exercise program can maintain or enhance upper extremity function and associated levels of interhemispheric inhibition.

The current study proposes the next logical step in my line of research and directly investigates the effects of exercise in an intervention with sedentary older Veterans (50-80 years), a group most likely to exhibit aging-related motor deficits. The investigators propose to enroll 40 Veterans into an upper extremity dexterity improvement program involving behavioral and exercise components. The behavioral intervention is a muscle coordination training previously shown to improve unimanual motor performance in older adults. The exercise intervention is a supervised group cycling regimen. The figure below shows the study design. Interhemispheric communication will be assessed with fMRI, and TMS.

Inclusion criteria

• Living persons between 60 and 85 years of age

Exclusion criteria

• unmanaged diabetes
• participants completing vigorous exercise per week
• participants whose profession requires vigorous physical labor
• contraindication to magnetic resonance imaging