Are cervical multifidus muscles active during whiplash and startle? An initial experimental study

Area of Science:

• Biomechanics of the cervical spine
• Neuromuscular responses to trauma
• Musculoskeletal injury mechanisms

Background:

• Cervical multifidus muscles attach to facet capsular ligaments, which can be a pain source in chronic whiplash.
• Reflex activation of multifidus muscles during whiplash may injure these ligaments.

Purpose of the Study:

• To investigate the onset latency and activation amplitude of cervical multifidus muscles.
• To assess responses to simulated rear-end collisions and loud acoustic stimuli.

Main Methods:

• Wire electromyography (EMG) electrodes were placed in the cervical multifidus muscles (C4 and C6 levels) of 9 subjects.
• Subjects were exposed to forward acceleration (1.55 g, 1.8 km/h) and a loud acoustic tone (124 dB).

Main Results:

• Multifidus activity was observed in most subjects (8/9) after both stimuli.
• No significant differences in onset latency or EMG amplitude were found between stimulus types or spine levels.
• EMG activity occurred within 160 ms of stimulus onset in 7 subjects.

Conclusions:

• Cervical multifidus muscles exhibit early activation in response to whiplash-like stimuli.
• This rapid activation may enhance collision-induced stress on cervical facet capsular ligaments.
• These findings suggest a potential mechanism contributing to chronic whiplash pain.