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.