Characteristics of the triceps brachii tendon reflex in man

The quantitative characteristics of the triceps brachii tendon reflex have been investigated in nine healthy adults. Particular consideration was given to the normal latency and amplitude values in response to a standardized tendon percussion. The effects of Jendrassik maneuver, head position (tonic neck reflex influences) and elbow joint angle were also evaluated. The latency of the triceps brachii reflex (mean = 11.2 msec) under normal conditions was found to be substantially shorter than previously reported values for the monosynaptic response. These differences are apparently attributable to the different methods that have been used to elicit the reflex. The present results are shown to be quite compatible with the known conduction velocity properties of the radial nerve. The mean amplitude of the reflex (means = 1.6 mV) was shown to be significantly (p less than 0.05) influenced by head position and Jendrassik maneuver. The magnitude of these effects are interpreted with respect to the proportion of the motoneuron pool activated by Ia inputs. Their neurophysiological basis and clinical usefulness are also discussed briefly.