Background <p>The neck muscles play a crucial role in maintaining cervical spine stability. A thorough understanding of the changes in neck muscles during cervical instability (CI), along with an analysis of their correlation with lifestyle habits, can provide valuable data for the prevention and treatment of CI.</p> Methods <p>A total of 98 patients with CI and 88 healthy subjects were included in the study. Their cervical MRI images and lifestyle habits information were collected. The relative cross-sectional area (RCSA) and fat signal fraction (FSF) of the neck muscles were obtained from the MRI images. Correlation analysis was conducted between the muscle parameters, CI, and lifestyle habits information.</p> Results <p>CI subjects spent more time working (<i>P</i> =.026) and using computers daily than the healthy subjects (<i>P</i> =.023). The cervical curvature of the CI subjects was significantly smaller compared to healthy subjects (<i>P</i> =.004). CI subjects had significantly smaller RCSA (<i>P</i> =.003) and greater FSF (<i>P</i> =.011) in the deep muscles at the back of the neck compared to healthy subjects. FSF in the deep muscles at the back of the neck (OR = 2.343, 95%CI = 1.261–4.352) and cervical curvature (OR = 0.904, 95%CI = 0.848–0.965) were risk factors for CI. Keeping head down time per day (r = - 0.286) and using the computer time per day (r = - 0.230) were negatively correlated with the RCSA in the deep muscles at the back of the neck.</p> Conclusions <p>Changes in the deep muscles at the back of the neck are key factors in the development of CI. Prolonged maintenance of a single downward head posture is closely related to changes in the deep muscles at the back of the neck.</p> Trial registration <p>The study protocol is registered with Chinese Clinical Trial Registry (registration number: ChiCTR2100053525, registration date: November 24, 2021).</p>