Dr. Eric J. Perreault’s upcoming seminar will discuss how the nervous system flexibly coordinates shoulder muscle activity to maintain stability while simultaneously providing the mobility required to complete everyday tasks.

Abstract

The neural and musculoskeletal systems are intimately linked in the control of movement and posture. The musculoskeletal system serves as a mechanical interface between the computations of our nervous system and our ability to physically interact with the world around us. Our laboratory works at the intersection of biomechanics and motor systems neuroscience. Our engineering focus is on developing tools to noninvasively quantify the mechanisms underlying the neural control of limb mechanics, and our scientific focus in on using those tools to better understand neuromechanical control in healthy and impaired populations. This talk will review some of our recent work on the human shoulder.

The shoulder is the most complex and mobile joint in the human body, but this mobility comes at a cost as it is also the joint most likely to dislocate. Appropriately regulating the mechanical properties of the shoulder therefore is critical for maintaining stability and controlling motion of the upper limb during activities of daily living. We have been conducting experiments to quantify the neural and biomechanical factors contributing to shoulder mechanics for both the rotations that underly function and the translations that contribute to impairment. These have demonstrated global increases in the rotational impedance of the shoulder during the generation of even single degree-of-freedom isometric torques. This broad mechanical coupling subserving shoulder rotations is reinforced by distributed feedback control in which the stretch-sensitive reflexes to any given muscle exhibit complex patterns of gain-scaling that extend the functional concept of a myotatic unit to the three dimensions relevant to shoulder use. In contrast, simpler patterns of reflex coordination occur when the humeral head is translated within the glenoid, serving predominantly to activate the rotator cuff muscles and maintain joint stability. Together, these results highlight how the nervous system acts to facilitate shoulder mobility while also maintaining stability.