Mirror Neurons in Older Participants (Project MNOP): Acute Effects of Action Observation on Muscle Strength/Weakness and Neurophysiological Factors in Older Adults

A critical problem facing aging adults is muscle weakness. Whereas scientists have traditionally attributed the loss of muscle strength with aging to atrophic effects, emerging evidence suggests that impairments in the neuromuscular system's ability to voluntarily generate force plays a more central role than previously appreciated. One area that has not yet been investigated includes the role that observing another's actions - thereby activating mirror neurons - plays in muscle force generation. Therefore, the purpose of this study is to examine the acute effects of action observation on muscular strength, voluntary activation, and cortical excitability and inhibition in older adults. Following a thorough familiarization visit, twenty-five men and women ≥60 years of age will complete three action observation sessions in a randomized, counterbalanced manner: 1) observation of very strong hand/wrist contractions, 2) observation of very weak hand/wrist contractions, and 3) a control condition. Maximal voluntary contractions (MVCs) of the wrist flexors will be performed before and after observation sessions. Percent voluntary activation will be determined via the interpolated twitch technique. Single-pulse transcranial magnetic stimulation (TMS) and electromyographic (EMG) recordings from the flexor carpi radialis and first dorsal interosseous will be used to quantify cortical excitability and inhibition, via motor evoked potential amplitude and silent period duration, respectively. The hypothesis of this study is that observation of strong muscle contractions will acutely increase muscle strength, and such changes will be facilitated by enhanced corticospinal excitability and decreased inhibition. In contrast, it is hypothesized that observation of very weak contractions will cause no such efforts or even acute muscle weakness. Collectively, we propose that manipulation of mirror neurons is a worthwhile strategy for clinicians hoping to induce neuromuscular adaptations in older adults, particularly in settings where movement of a joint is painful or infeasible (e.g., bedrest or immobilization).