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This study examined the intraclass reliability of the latency and amplitude of the Hoffmann reflex (H-reflex) in the flexor carpi radialis (FCR). The stability and consistency of the latency and peak-to-peak amplitude of the H-reflex were assessed across four test sessions. The FCR H-reflex was evoked in 39 volunteers (20 males and 19 females) on four separate days. The maximum amplitude of the motor response (Mmax) was determined each day and 10 responses were recorded at that stimulus intensity. The H-reflex was then evoked at an intensity corresponding to 5% of Mmax (H5%) and 10 recordings were obtained. The latency of the H-reflex and the peak-to-peak amplitude of both Mmax and H5% were calculated for each trial. Determination of reliability involves the consideration of both the stability and consistency of the measures. The reliability of the measures in this investigation was assessed using an analysis of variance and corresponding Lindquist intraclass correlation coefficient (ICC) model. In contrast to previous investigations, the H-reflex was evoked without facilitation in 95% (37/39) of the subjects tested. Statistical evaluation revealed that the latency and amplitude of the H-reflex, as well as the amplitude of Mmax, were both stable and consistent across the four test days. The ICC for Mmax was 0.97. The ICC for H5% was 0.92, and for latency of the H-reflex was 0.89. It was shown that the H-reflex can be easily evoked in the FCR and that the latency and amplitude of these recordings are highly reliable. The demonstration that the H-reflex can be easily and consistently evoked in the FCR has important clinical implications. It provides a tool for clinicians to assess the C7 level of the spinal cord and median nerve function.

Objective: To measure the effects of manual segmental vibration (MSV) on motoneuron pool excitability., Methods: Seven healthy subjects were tested under five conditions: pretest, upholding static knee position (USKP), MSV, posttest 1 and posttest 2. Each test lasted 2 min, and a 2-min rest was given between pretest, USKP and MSV, whereas the last two tests were consecutive. Cutaneous pressure and vibration frequency were stabilized through training periods. The effects of MSV on motoneuron excitability were investigated by measuring the H-reflex peak-to-peak amplitude., Measures: The H-reflex and M response were taken from the medial gastrocnemius electromyogram and elicited every 7 sec by a 1 ms square wave pulses to the tibial nerve. Fifteen trials were recorded for each condition. Stimulation intensity was set at 10% (+/- 2.5%) of Mmax stimulus., Results: Repeated-measures analysis of variance comparing conditions revealed no significant differences in M response [F(4,24) = 2.37, p > .05, beta = .35]. H-reflex comparisons revealed significant differences [F(4,24) = 30.39, p < .05, beta = .01] between conditions. Duncan post hoc analysis showed that MSV produced the greatest inhibition (decreases 95%) and USKP also elicited a significant inhibition (decreases 41%)., Conclusions: The inhibition may be the result of the following mechanisms: the reflex inhibition, the implication of cutaneous afferences and the higher control mechanism. Because MSV produces a reduction in neuromuscular excitability, it could also play a role in predisposing the system for changes to occur and therefore be used as an adjunct for other therapeutic applications.

Objective: Determine the electrophysiological effects of anterior knee pain using monosynaptic and polysynaptic reflexes., Design: A pretest/posttest control group experimental design with repeated measures., Setting: All tests were performed in a university laboratory., Participants: Six subjects suffering from patello-femoral dysfunction (PFD) composed the experimental group. These patients were diagnosed and referred by medical and chiropractic doctors. Six healthy subjects were recruited for the control group., Intervention: Pain relief by cold application (10 minutes) on the knee., Main Outcome Measures: Monosynaptic reflex: H reflex of the superficial portions of the quadriceps femoris. Polysynaptic reflexes: nociceptive flexion response (NFR) of the long head of the biceps femoris., Results: Cold application, producing significant pain relief (p < 0.05), did not change H-reflex amplitude (p > 0.05) for both groups and did not show modulation of the NFR. However, the PFD group showed significantly lower pain (p < 0.05) and NFR thresholds (p < 0.05) than the control group. Finally, nociceptive stimulation was applied at the sural nerve during an isometric extension of the knee (20% of maximum electromyographic contraction). After this stimulation, uni-articular extensors, especially the distal fibers of the vastus medialis, showed a longer and stronger inhibition than the bi-articular rectus femoris., Conclusions: Pain episodes do not appear to affect monosynaptic responses. NFR threshold differences found between PFD and control group could be explained by the increased excitability of the nervous system in subjects experimenting painful bouts. Functional implications of these findings are discussed.