The effects of cervical high-velocity low-amplitude thrust manipulation on resting electromyographic activity of the biceps brachii muscle

Abstract

There is a gap in the literature regarding the effects of spinal manipulation on extremity muscles that are unconnected to the vertebral column by an origin or insertion. This study investigated the effect of a right C5/6 high-velocity low-amplitude thrust (HVLAT) manipulation on resting electromyographic activity of the biceps brachii muscles bilaterally.

A placebo-controlled, single-blind, repeated measures design employed an asymptomatic convenience sample (n = 54) investigating three conditions: HVLAT, sham, and control.

HVLAT demonstrated an excitatory effect with increased EMG activity of 94.20% (P = 0.0001) and 80.05% (P = 0.0001) for the right and left biceps respectively. A one-way repeated measures ANOVA revealed a significant difference (P = 0.0001) in the mean percentage change of resting EMG activity, as did post hoc analyses (P = 0.0001) between all three conditions. Subjects not experiencing cavitation post HVLAT demonstrated greater EMG increases for both right (P = 0.0001) and left (P = 0.014) biceps than those experiencing cavitation. The magnitude of mean EMG change for the right biceps was significantly greater than the left (P = 0.011) post HVLAT.

This study demonstrates a single HVLAT to the right C5/6 zygapophyseal joint elicits an immediate increase in resting EMG activity of the biceps bilaterally, irrespective of whether or not cavitation occurs.

Introduction

Spinal mobilisation and manipulation have been used for more than 2000 years in the treatment of neuromusculoskeletal disorders (Curtis, 1988). The effects of mobilisation and high-velocity low-amplitude thrust (HVLAT) manipulation have been an area of focus for recent research. Several studies have demonstrated that mobilisation and HVLAT of the cervical spine produce hypoalgesic effects through increased pressure pain thresholds in symptomatic and asymptomatic subjects (Cassidy et al., 1992, Vicenzino et al., 1995, Vicenzino et al., 1998, Sterling et al., 2001, Fernandez-de-las-Penas et al., 2007). In addition, several studies have demonstrated mobilisation of the cervical spine in asymptomatic and symptomatic populations stimulates the peripheral sympathetic nervous system resulting in decreased blood flow and skin temperature, and increased skin conductance in the upper extremities (Petersen et al., 1993, Vicenzino et al., 1998, Sterling et al., 2001). However, there is conflicting evidence regarding the excitatory (Herzog et al., 1999, Suter et al., 1999, Keller and Colloca, 2000, Symons et al., 2000, Suter et al., 2000, Colloca and Keller, 2001, Dishman et al., 2002, Suter and McMorland, 2002) or inhibitory (Dishman and Bulbulian, 2000, Lehman and McGill, 2001, Lehman et al., 2001, DeVocht et al., 2005) nature of the neurophysiological response that occurs after HVLAT manipulation of the spine. The methodological quality of these studies is poor; with only three studies (Keller and Colloca, 2000, Suter et al., 2000, Dishman et al., 2002) utilising control or placebo groups. In addition, only two studies (Dishman and Bulbulian, 2000, Dishman et al., 2002) administered a single unilateral HVLAT manipulation to each subject; with the remaining studies administering multiple bilateral HVLAT manipulations, and in some studies to multiple spinal regions. Conclusions cannot therefore be made regarding the excitatory or inhibitory nature of reflexive muscular response post HVLAT.

HVLAT to segmentally associated zygapophyseal joints has demonstrated transient reflexic contractions of local paraspinal muscles using electromyography in asymptomatic (Herzog et al., 1999, Symons et al., 2000) and symptomatic subjects (Colloca and Keller, 2001). After lumbar HVLAT in LBP subjects, immediate increases in muscle strength of the erector spinae have been demonstrated (Keller and Colloca, 2000). Equally, however, an immediate reduction in paraspinal electromyographic activity post HVLAT in asymptomatic (Dishman and Bulbulian, 2000) and LBP patients (Lehman and McGill, 2001, DeVocht et al., 2005) has been demonstrated and again it remains unclear whether HVLAT produces an excitatory or inhibitory effect on paraspinal muscle activity.

There is a gap in the literature regarding the effects of HVLAT on extremity muscles unconnected to the vertebral column by an origin or insertion. Herzog et al. (1999) assessed the effects of HVLAT to the spine on resting EMG activity of deltoid and found an ipsilateral reflex muscle contraction of deltoid post HVLAT. However, this was a limited study (n = 10) with no control or placebo, and each subject received 11 HVLAT manipulations to the cervical, thoracic, lumbar and pelvic regions. In addition, Herzog et al. (1999) did not report the magnitude of the response, only the percentage of positive responses occurring when the signal increased to at least three times the baseline value. Suter and McMorland (2002) demonstrated an immediate 7–10 N.m increase in elbow flexor torque post HVLAT of the cervical spine; however, again the results must be interpreted cautiously because no control or placebo groups were utilised and multiple HVLAT manipulations were administered on all subjects.

Several authors (Indahl et al., 1997, Herzog et al., 1999, Symons et al., 2000, Pickar and Kang, 2006) have proposed that the neurophysiologic pathway of the observed electromyographic response following HVLAT involves activation of the mechanoreceptors in the zygapophyseal joint capsule, spinal ligaments, and intervertebral disc, the cutaneous receptors, and the muscle spindles and golgi tendon organs within the muscle belly and tendon of the associated muscles. Alteration in afferent discharge rates from the stimulation of these receptors following HVLAT manipulation is thought to cause changes in alpha motorneuron excitability levels with subsequent changes in muscle activity (Indahl et al., 1997, Dishman and Bulbulian, 2000, Suter et al., 2000, Symons et al., 2000). However, this proposal is not fully supported by their research (Herzog et al., 1999, Symons et al., 2000) as only Pickar and Kang (2006) directly measured mechanoreceptor or proprioceptor activity. Furthermore, Pickar and Kang (2006) only measured the muscle spindle discharge rates in non-human subjects.

There has been some debate in the literature surrounding the role of cavitation (an audible “pop” or “crack”) during HVLAT and the observed effects. Herzog et al. (1993a) found reflex responses in the paravertebral muscles irrespective of whether cavitation was achieved. Likewise, Dishman and Bulbulian (2000) found similar reflexic responses in the lumbar spine following either mobilisation without cavitation or manipulation with cavitation, and proposed that the velocity dependent facet joint mechanoreceptors were not implicated in the neurophysiologic response. In contrast, Suter et al. (1994) were not able to elicit electromyographic reflex responses from non-cavitation thrust manipulations given at a low-velocity, i.e. at a rate greater than 1 s compared with 100–150 ms for high-velocity thrusts; however, no control or placebo conditions were employed and the findings cannot be attributed to the intervention. The question therefore remains whether the cavitation phenomenon is required to facilitate a neurophysiological response in resting muscle activity post HVLAT.

To date, no controlled study has investigated the effects of cervical HVLAT manipulation on resting muscle activity more distal than the deltoid (Herzog et al., 1999, Suter and McMorland, 2002) or on contralateral upper extremity muscle activity. The purpose of this study was to characterise the nature (excitatory or inhibitory) and the magnitude of any change in resting electromyographic activity of the biceps brachii muscle post C5/6 HVLAT ipsilaterally and contralaterally. In addition, the relationship to joint cavitation was explored. The biceps brachii muscle was selected as it is anatomically unconnected to the area of intervention through origin or insertion, but is segmentally linked from a neurophysiological perspective.