Cervical Spine Range of Motion Reliability with Two Methods and Associations with Demographics, Forward Head Posture, and Respiratory Mechanics in Patients with Non-Specific Chronic Neck Pain

<b>Objectives</b>: New smartphone-based methods for measuring cervical spine range of motion (CS-ROM) and posture are emerging. The purpose of this study was to assess the reliability and validity of three such methods in patients with non-specific chronic neck pain (NSCNP). <b>Methods</b>: The within-day test-retest reliability of CS-ROM and forward head posture (craniovertebral angle-CVA) was examined in 45 patients with NSCNP. CS-ROM was simultaneously measured with an accelerometer sensor (KFORCE Sens^®) and a mobile phone device (iHandy and Compass apps), testing the accuracy of each and the parallel-forms reliability between the two methods. For construct validity, correlations of CS-ROM with demographics, lifestyle, and other cervical and thoracic spine biomechanically based measures were examined in 90 patients with NSCNP. Male-female differences were also explored. <b>Results</b>: Both methods were reliable, with measurements concurring between the two devices in all six movement directions (intraclass correlation coefficient/ICC = 0.90-0.99, standard error of the measurement/SEM = 0.54-3.09°). Male-female differences were only noted for two CS-ROM measures and CVA. Significant associations were documented: (a) between the six CS-ROM measures (R = 0.22-0.54, <i>p</i> < 0.05), (b) participants' age with five out of six CS-ROM measures (R = 0.23-0.40, <i>p</i> < 0.05) and CVA (R = 0.21, <i>p</i> < 0.05), (c) CVA with two out of six CS-ROM measures (extension R = 0.29, <i>p</i> = 0.005 and left-side flexion R = 0.21, <i>p</i> < 0.05), body mass (R = -0.39, <i>p</i> < 0.001), body mass index (R = -0.52, <i>p</i> < 0.001), and chest wall expansion (R = 0.24-0.29, <i>p</i> < 0.05). Significantly lower forward head posture was noted in subjects with a high level of physical activity relative to those with a low level of physical activity. <b>Conclusions</b>: The reliability of both CS-ROM methods was excellent. Reductions in CS-ROM and increases in CVA were age-dependent in NSCNP. The significant relationship identified between CVA and CWE possibly signifies interconnections between NSCNP and the biomechanical aspect of dysfunctional breathing.