The H-reflex as a tool in neurophysiology: its limitations and uses in understanding nervous system function.

The Hoffmann reflex (H-reflex) is extensively used as both a research and clinical tool. The ease with which this reflex can be elicited in several muscles throughout the body makes it an attractive tool. This review discusses some of the important limitations in using the H-reflex. In particular, the inaccurate but widely held assumptions that the H-reflex (1). represents the monosynaptic reflex of the Ia afferent onto homonymous motoneurons, and (2). can be used to measure motoneuronal excitability are addressed. The second part of this review explores the utility of the H-reflex as a neural probe in neurophysiology and motor control research. Applications ranging from the investigation of the functional organization of neural circuitry to the study of adaptive plasticity in spinal structures in health and disease suggest that the H-reflex will continue to be an extensively used tool in motor control neurophysiology.