Study Design
Muscle use evoked by exercise was determined by quantifying shifts in signal relaxation times of T2-weighted magnetic resonance images. Images were collected at rest and after exercise at each of two intensities (moderate and intense) for head movements: 1) extension, 2) flexion, 3) rotation, and 4) lateral flexion.
Objective
This study examined the intensity and pattern of neck muscle use evoked by various movements of the head. The results will help elucidate the pathophysiology, and thus methods for treating disorders of the cervical musculoskeletal system.
Summary of Background Data
Exercise-induced contrast shifts in T2 has been shown to indicate muscle use during the activity. The noninvasive nature of magnetic resonance imaging appears to make it an ideal approach for studying the function of the complex neuromuscular system of the neck.
Methods
The extent of T2 increase was examined to gauge how intensely nine different neck muscles or muscle pairs were used in seven subjects. The absolute and relative cross-sectional area of muscle showing a shift in signal relaxation was assessed to infer the pattern of use among and within individual neck muscles or muscle pairs.
Results
Signal relaxation increased with exercise intensity for each head movement. The absoluta and relative cross-sectional area of muscle showing a shift in signal relaxation also increased with exercise load. Neck muscles or muscle pairs extensively used to perform each head movement were: extension-semispinalis capitls and cervicis and splenius capitis; flexion-sternocleidomastold and longus capitis and collirotation-splenious capitis, levator scapulae, scalenus, semispinalis capitis ipsilateral to the rotation, and sternocleidomastold contralateral; and lateral flexion-sternocleidomastoid.
Conclusion
The results of this study, in part, agree with the purported functions of neck muscles derived from anatomic location. This also was true for the few selected muscles that have been examined in human electromyographic studies. Neck muscle function and morphology can be studied at a detailed level using exercise-induced shifts in magnetic resonance images.
