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Thur, August 5

Speaker: Daniel Ludvig, M.Eng.

Title: Task-Dependent Modulation of Joint Stiffness

Abstract: Joint stiffness defines the dynamic relationship between the position of the joint and torque acting about it; hence it is important in the control of movements and posture. Joint stiffness consists of two components: intrinsic stiffness, which is due to the viscoelastic properties of the joint, muscle, and connective tissue and the inertia of the limb; reflex stiffness, which arises due to the torque produced by the stretch reflex response. Numerous studies have investigated whether subjects can modulate their reflex stiffness voluntarily but have produced contradictory results; a possible reason for this uncertainty is the lack of a proper feedback to provide to subjects. Using intrinsic and reflex stiffness estimates generated by a novel algorithm as feedback, subjects showed the ability to control reflex stiffness independently of intrinsic stiffness. However, when given a task that would be performed optimally by modulating their joint stiffness, subjects produced voluntary torques based on visual feedback, rather than modulating their joint stiffness. These voluntary torques were found to be correlated to the velocity of the visual feedback. Thus, subjects can modulate their joint stiffness is numerous ways—by altering intrinsic stiffness, reflex stiffness or voluntary components. However, it remains to be determined whether there exist tasks, which would motivate subjects to modulate their stiffness in a task-dependent manner.

Host: Eric Perreault