Neck muscle activation patterns in humans during isometric head stabilization

Abstract

A musculoskeletal system with more muscles than there are motions could be programmed in alternative ways to produce a single movement. In this case, the muscles would have the potential to be maximally responsive in multiple directions rather than responding preferentially in a single direction. To determine the response patterns of muscles in the head-neck motor system, the simultaneous activation of four of the 23 neck muscles acting on the head was recorded with both surface and intramuscular electrodes. Fifteen human subjects were tested during an isometric head stabilization task. When the EMG response patterns were plotted, each muscle demonstrated a preferred direction of activation. This preferred activation direction was consistent in all of the subjects for three of the muscles tested. The fourth muscle, splenius, was preferentially activated during neck flexion in half of the subjects and during neck extension in the other half. Increasing the force parameters of the task suggested a linear relationship between force and the EMG output in the preferred response directions. Responses in the nonpreferred directions were produced by a nonlinear change in EMG activation of the muscle. This finding could have implications for theories of how reciprocal activation and cocontraction patterns of response are elicited. Results from this study, that the CNS programs neck muscles to respond in specific orientations rather than generating an infinite variety of muscle patterns, are in agreement with our findings in the cat.

Patterns of neck muscle activation in cats during reflex and voluntary head movements

“…Second, although the pattern of muscle activation in each cat was consistent within a task, axes of maximal activation differed between the reflex and voluntary responses (e.g., splenius exhibited greater activation in the pitch and roll rotations during voluntary tracking, and in the yaw and pitch rotations during reflex testing). Third, as found in decerebrate cats (Baker and Wickland 1988) and humans (Keshner et al 1989), the best excitation of the muscle was not always in the plane that would produce a maximum mechanical advantage for the muscle based on its line of pull.…”

“…The cervicocollic reflex (CCR) also counteracts unplanned head movements, but as a result of movements of the head relative to the trunk which stimulate proprioceptive inputs at the neck . Descending signals can occur prior to movement as preprogrammed motor commands, or can modify stimulus-response relations according to the specific task constraints (Guitton et al 1986;Keshner et al 1989). Finally, head position is influenced by biomechanical forces arising within the head-neck motor plant which has a unique morphology with its inertial mass sitting atop a flexible column composed of multiple joints and ligaments (Vidal et al 1986).…”

Changes in Dorsal Neck Muscle Function in Individuals with Chronic Whiplash-Associated Disorders: A Real-Time Ultrasound Case–Control Study

“…Healthy individuals exhibit different preferred activation of the splenius as a neck extensor or flexor , Keshner et al 1989, synchronized neuronal drive between deep and superficial muscles , and different activation strategies among individuals during a reflexive task ). Individuals with WAD had less defined activity in the deep semispinalis capitis (Schomacher et al 2012) and higher activity in the superficial neck extensor has been reported (Juul-Kristensen et al 2013), but when controlling for movement velocity, the acceleration or deceleration peak in the splenius was not different from that of healthy controls (Vikne et al2013).…”

“…Different EMG tests result in different neck muscle activation patterns; if the head is firmly clamped and force applied to the head, preferred activation was seen in the neck muscles except for the splenius capitis (Keshner et al 1989, whereas more individual muscle responses occur during reflexive movements ).…”

“…Functional MRI studies have reported altered neck muscle activity after induced pain in healthy individuals ) and in individuals with neck pain ). Electromyography (EMG) studies have shown that not all dorsal muscles act synergistically as extensors; the splenius capitis muscle can activate during neck flexion in some healthy individuals (Keshner et al 1989) and higher levels of extensor muscle co-activation in neck pain have been reported (Lindstrom et al 2011). Surface EMG has demonstrated increased activity in superficial neck extensors in WAD (Bexander et al 2012, Juul-Kristensen et al 2013), but when controlling for differences in movement velocity, no differences were found between WAD and healthy controls (Vikne et al 2013).…”