Introduction:​ In British Columbia, whiplash injuries and its associated disorders are serious economical and social burdens to society. Despite affecting less than 1 percent of the population, whiplash injuries costs of over 850 million dollars annually (ICBC 2007). In recent studies, the startle response was shown to form part of the neuromuscular response to whiplash-like perturbations (Blouin et al. 2006a and b). In non-whiplash experiments, a weak or startling pre-stimulus tone presented before a subsequent startling stimulus can inhibit the startle response (Ison and Krauter 1974;​ Valls-Sole et al. 2005). The objective of the present study was to investigate how different pre-stimulus tones (weak and startling) affected the amplitude of muscle responses and the peak magnitude of head kinematics observed in human volunteers during whiplash-like perturbations.

Methods:​ Twenty healthy subjects experienced five consecutive whiplash-like perturbations presented simultaneously with a loud collision sound (109 decibels (dB)). The three experimental conditions differed with the intensity of pre-stimuli tone presented 250 milliseconds prior to the onset of the perturbation:​ 1.) no pre-stimulus tone (Control), 2.) a weak pre-stimulus tone (85dB) and 3.) a startling pre-stimulus tone (105dB). Electromyography (EMG) of neck and distal limb muscles, and kinematics of the head and trunk were simultaneously collected. Mixed model ANOVAs and post-hoc Tukey’s honest significant difference test were used to analyze each EMG and kinematic variable (alpha=0.05).

Results:​ Presenting a startling pre-stimulus tone before the whiplash-like perturbation decreased muscular (sternocleidomastoid:​ ~16%, C4 paraspinal:​ ~26%, biceps brachii:​ ~66%, triceps brachii:​ !62%, first dorsal interosseous:​ ~68%, and rectus femoris:​ 78%) and kinematic (peak retraction:​ ~17%, peak horizontal acceleration of the head:​ ~23%, and peak head angular acceleration in extension:​ ~23%) responses from Control condition (p<0.05). A weak pre-stimulus tone decreased only the muscular responses of triceps brachii (~38%), first dorsal interosseous (~48%) and rectus femoris (~57%) from Control condition (p<0.01).

Conclusion:​ A startling tone presented prior to a whiplash-like perturbation alters the head-neck responses in ways that are consistent with reducing neck tissue strains. This study is an initial step in the development of preventive devices to decrease the whiplash injury potential during low-speed, rear-end automotive collisions.