Endurance and fatigue characteristics of the neck flexor and extensor muscles during isometric tests in patients with postural neck pain.

Sustained postural loading of the cervical spine during work or recreational tasks may contribute to the development of neck pain. The aim of this study was to compare neck muscle endurance and fatigue characteristics during sub-maximal isometric endurance tests in patients with postural neck pain, with asymptomatic subjects. Thirteen female patients with postural neck pain and 12 asymptomatic female control subjects completed timed sub-maximal muscle endurance tests for the neck flexor and extensor muscles. Muscle fatigue, defined as the time-dependent decrease in median frequency electromyography (EMG), was examined using surface EMG analysis during the tests. The median extensor test holding time was lower but not significantly different in the neck pain group (165 s) that the control group (228 s) (p = 0.17). There was no difference between groups in the flexor test holding time (neck pain = 36 s, controls = 38 s) (p = 0.96). The neck pain group was characterised by greater variability in neck flexor (p = 0.03) and extensor (p = 0.006) muscle endurance. For both tests, the rate of decrease in median frequency EMG was highly variable within and between groups with no significant difference between groups for the flexor or extensor test (p = 0.05-0.82). Patients with postural neck pain did not have significant impairment of neck muscle endurance or accelerated fatigue compared to control subjects. However, the greater variability in these indices of muscle function may reflect patient-specific changes in muscle function associated with neck pain disorder.