The Use of Short- and Long-Latency Reflex Testing in Leg Muscles of Neurological Patients

Hammond [27, 28] originally described electromyographic (EMG) responses of long latency, which were evoked 50 ms later than the stretch reflex, when the biceps brachii muscle was suddenly extended and the subject was instructed to resist the displacement. These EMG responses were considered to be “automatic” in nature, for their latency was 40 ms shorter than the fastest voluntary reaction to a mechanical stimulus. There has been a long controversy as to the possible pathway and generators as well as the function of “long-loop reflexes” (for reviews see [8, 12, 13, 57]). Despite the fact that different types of EMG responses can be evoked from finger, hand, arm, and leg muscles labelled with a varying terminology, there are some common features of these long-latency responses. The best way to generate them is a sudden angular displacement of the joint with a certain minimal velocity and duration [5, 8, 34]. Prestretching or loading of the stretched muscle is required but can be replaced by an instruction given to the subject to resist the imposed displacement. Functional requirements obviously determine strength and temporal pattern of these responses [15, 30].