Is the clinical cervical extensor endurance test capable of differentiating the local and global muscles?

Differential alterations have been reported in the local and global cervical muscles in the presence of chronic neck pain (CNP), including the endurance alterations of these muscles. Identifying the involved muscles is crucial to the assessment and rehabilitation of patients with CNP.

To assess the relationship between clinical endurance test results, pain and disability indices, and ultrasonographic (US) measurements of the neck extensor muscles; to compare the deep and superficial cervical extensor muscle endurance and size of CNP patients with those of asymptomatic subjects and to compare the relationship between local and global extensor endurance with US measures, pain intensity, and disability.

Cross-sectional correlational analysis with a case-control design.

Thirty patients with CNP and 30 asymptomatic subjects participated in this study.

Endurance, thickness, cross-sectional area, and shape ratio of the cervical extensor muscles (splenius capitis [SpCap], semispinalis capitis [SSCap], semispinalis cervicis [SSCer], and multifidus [MF]); pain intensity measured by the visual analog scale (VAS); neck disability index (NDI); correlation between US measures, pain intensity and NDI and extensor endurance; and correlation of US measures with pain intensity and NDI.

The deep and superficial cervical extensor muscle endurance and dimensions were measured via a clinical test and by US, respectively. Participants were asked to hold the neutral chin-tuck position while lying prone. The test would be terminated if the head moved into either flexion or extension, which would yield "global" or "local" extensor muscle endurance, respectively.

The CNP patients showed lower global extensor endurance levels than the control participants (p<.05). The US measures of the deep extensor muscles were also smaller in the CNP group (p<.05). There were no significant correlations between extensor endurance test results and US measures in either group except for the SSCap muscle size with local and total endurance (p=.04 for both) of CNP and control participants, respectively. NDI was correlated with SpCap and SSCer muscle thicknesses in a positive and negative manner, respectively (p=.03 for both). There was also a significant correlation between MF size and VAS (p<.05).

The findings showed higher levels of global muscle fatigability and smaller size of deep neck extensor muscles in CNP patients. Disability and extensor endurance were found to be associated with extensor muscle size. The results challenge the validity of the clinical extensor muscle endurance test in the differentiation of the deep and superficial extensor muscle endurance and the use of US in the assessment of cervical muscle endurance. Further investigations are needed to judge the superficial and deep muscle endurance in CNP patients.