Abstract

Although the medium latency EMG response (ML) to limb perturbation was observed in 1954 by Hammond, the physiological role of this response has remained a mystery. We hypothesize that this medium latency EMG response functions to pre-set stiffness of the limb to a constant initial level. A prediction from this hypothesis is that in the presence of an instruction calling for opposition to limb perturbation, a control signal, ML, will be observed and will lead to the establishment of a constant level of limb stiffness. This hypothesis was tested in experiments involving perturbation ofthe human forearm about the elbow joint. Surface EMG on the biceps and tricepswere simultaneously measured, and the limb stiffness function was computed. When subjects wereasked to oppose ramp perturbations, ML was observed, followed by a prolonged plateau of constant limb stiffness. These findings arein accord with the hypothesis put forth. Verf.-Referat