Myofascial trigger points: does recent research gives new insights into the pathophysiology? by ProQuest


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                                                                                                    soleus muscle). The electrical stimulus over
Myofascial trigger points: does recent                                                              the nerve is increased until the H-reflex

research gives new insights into the                                                                appears (typically 4–10 mA), which corre-
                                                                                                    sponds to stimulation of the Ia muscle

pathophysiology?                                                                                    spindle afferents (MSAs)—Ia MSAs are the
                                                                                                    largest diameter and fastest conducting
                                                                                                    nerves. A monosynaptic (or oligosynaptic)5
Mike Cummings                                                                                       reflex results in stimulation of the asso-
                                                                                                    ciated Aa motor nerves. At higher stimulus
                                                                                                    intensities the M-wave appears—this is
                                                                                                    caused by direct stimulation of the Aa
The paper by Ge et al1 (see page 150) may be      nerve stimulus) appears to be significantly       motor nerves to the muscle. The H-reflex
an important milestone in the investigation       greater when elicited from within an              appears before the M-wave because the Ia
of the pathophysiological substrate of the        MTrP than from within normal muscle               MSAs have a lower electrical threshold
myofascial trigger point (MTrP). The paper        tissue (non-MTrP).                                than the Aa motor nerves.
appears to show that there is a significantly        The H-reflex was first described in 1910          In the paper by Ge et al the M-wave
reduced threshold and increased amplitude         by the German physiologist Paul                   was stimulated from within muscle,
of an electrophysiological reflex (similar to     Hoffmann.2 It is an electrophysiological          either by intramuscular stimulation of
the Hoffman (H-) reflex) when it is stimu-        equivalent of the stretch reflex (usually         Aa motor nerves or by direct depolarisa-
lated electrically from within an MTrP            elicited as a tendon jerk in the physical         tion of muscle cell walls. Despite this, the
compared with normal muscle nearby.               examination), but it bypasses the muscle          latency of the M-wave recorded from
   It appears to be the first paper in which      spindle.3 It is used in research as a non-        surface EMG was similar whether elicited
an electrophysiological reflex similar to         invasive neurophysiological probe to              by stimulation of the tibial nerve or
the H-reflex has been recorded following          study the neural control of movement.3 4          elicited by intramuscular stimulation—
an intramuscular electrical stimulus. The         The H-reflex is stimulated by a transcu-          presumably because the speed of trans-
important finding of the paper is that the        taneous electrical impulse (square wave of        mission of a muscle action potential is
amplitude of this reflex as a proportion of       short duration, ie, 0.5–1 ms) over a major        some 13 times slower than the nerve
the maximum direct muscle stimulus                nerve (eg, the tibial nerve behind the            action potential in the Aa motor nerves.6
effect (measured peak to peak from the            knee) and recorded with EMG electrodes               We need to be cautious in our inter-
M-wave—the electromyography (EMG)                 over a muscle in the motor distribution of        pretation of the result in Ge et al, since the
recording of the direct muscle or motor           the same nerve (eg, the gastrocnemius or          H-reflex is not generally stimulated from

Figure 1 This figure shows a monosynaptic reflex arc including a muscle spindle Ia afferent nerve (green) and a Aa motor efferent nerve (blue). The
insulated EMG needle is likely to be closer to muscle spindle Ia afferent nerves when placed in an MTrP than when placed in non-MTrP muscle.

148                                                                                                          Acupunct Med December 2009 Vol
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