BIEWENER, Andrew A.; Harvard University: Neuromuscular dynamics: passive versus active control of locomotion and stability.

Neuromuscular control of movement depends on matching neural commands to the time-varying requirements of muscle force generation and length change of multiple muscle groups within an animal�s limbs and body. In addition to motor unit characteristics, muscle-tendon architecture is likely key to the roles that particular muscle groups play in the support and movement of the body. Direct recordings of muscle force, length change, and activation (EMG) enable the in vivo dynamics of muscles to be examined while animals perform a range of motor tasks. Recent studies show that whereas more distal muscles may favor economical force generation with minimal length change and little net work output, more proximal muscles shorten or lengthen to modulate overall limb work. Current work examines how regional patterns of work modulation are achieved with respect to differing motor tasks (grade vs level, steady vs acceleration) and how these are controlled by the pattern of neural activation. Perturbations to an animal�s stability (maintenance of center of mass trajectory) require rapid, dynamic adjustments to correct and control the motion of limb segments and the body. While intrinsic biomechanical properties of muscle-tendon units (force-length and force-velocity), sometimes referred to as �preflexes�, may facilitate neuromuscular control, rapid neuromuscular feedback via muscle-tendon afferents is also likely to be important, and integrated with the animal�s passive dynamics, to stabilize movement at faster speeds. (Supported by NIH AR047679).