The hoffmann reflex: methodologic considerations and applications for use in sports medicine and athletic training research

Abstract

Objective: To discuss the proper methods used to elicit the Hoffmann reflex (H-reflex) and to present different situations in which this tool can be used in sports medicine research.

Data sources: We searched MEDLINE and SPORT Discus from 1960 to 2004 using the key words Hoffmann reflex, H-reflex, and methodology. The remaining citations were collected from references of similar papers.

Data synthesis: Numerous authors have used the H-reflex as a tool to examine neurologic conditions. However, few have used the H-reflex to examine neuromuscular impairments after sport injuries. Several studies were available describing the appropriate methods to elicit the H-reflex and examining the reliability of this measurement in different muscles.

Conclusions/recommendations: The H-reflex is a valuable tool to evaluate neurologic function in various populations. However, because of the sensitivity of this measurement to extraneous factors, care must be taken when eliciting the H-reflex. We discuss recommendations on how to elicit the H-reflex and how to appropriately present methods in a manuscript.

Figures

Figure 1

Hoffmann reflex (H-reflex) and muscle response (M-wave) pathways. When a short-duration, low-intensity electric stimulus is delivered to the tibial nerve, action potentials are elicited selectively in sensory Ia afferents due to their large axon diameter (response 2). These action potentials travel to the spinal cord, where they give rise to excitatory postsynaptic potentials, in turn eliciting action potentials, which travel down the alpha motor neuron (αMN) axons toward the muscle (response 3). Subsequently, the volley of efferent action potentials is recorded in the muscle as an H-reflex. Gradually increasing the stimulus intensity causes action potentials to occur in the thinner axons of the αMNs (response 1), traveling directly toward the muscle and recorded as the M-wave. At the same time, action potentials propagate antidromically (backward) in the αMN toward the spinal cord (response 1) to collide with action potentials of the evoked reflex response (response 3), thereby resulting in partial cancellation of the reflex response. At supramaximal stimulus intensities, orthodromic (toward the muscle) and antidromic (toward the spinal cord) action potentials occur in all MN axons; the former gives rise to a Mmax, whereas the latter results in complete cancellation of the H-reflex. Figure adapted with permission from Aagaard P, Simonsen EB, Andersen JL, Magnusson P, Dyhre-Poulsen P. Neural adaptation to resistance training: changes in evoked V-wave and H-reflex responses. J Appl Physiol. 2002;92:2309–2318.

Figure 2

Recruitment curve. The stimulus intensity is set at 0 and gradually increased until maximum Hoffmann reflex amplitude and maximum muscle response amplitude are achieved.

Figure 3

Summary of events leading to the appearance of the Hoffmann reflex (H-reflex) and muscle response (M-wave) and to the disappearance of the H-reflex. A, Electric stimulus elicits a response in only Ia afferent fibers, causing orthodromic impulses toward the spinal cord and resulting in the firing of alpha motor neurons and appearance of the H-reflex on the electromyograph (EMG). B, Electric stimulus elicits a response in Ia afferents and also directly activates the motor axons. The stimulus does not activate all motor axons, and, thus, the antidromic impulses do not collide with all action potentials that resulted from the orthodromic activity. The H-reflex is still apparent (it would be considered on the descending part of the recruitment curve) on the EMG, and the M-wave is now apparent. C, Electric stimulus results in activation of all motor axons. Antidromic collision blocks all action potentials that were the result of orthodromic activity, and, therefore, only the maximum M-wave appears on the EMG.

Figure 4

A. Example of a unipolar electrode setup used to elicit the soleus Hoffmann reflex. The cathode (active electrode) is placed in the popliteal fossa over the posterior tibial nerve, whereas the cathode (inactive or dispersive electrode) is placed superior to the patella. This setup allows for the current to be delivered through the active electrode in the direction of the dispersive electrode. B. Example of a bipolar setup. Both the anode and cathode are contained in one electrode. The current travels back and forth between the negative and positive poles.