Test-retest reliability of longus colli muscle size using musculoskeletal ultrasound during craniocervical flexion test

Background Musculoskeletal ultrasound is a safe, non-invasive technique for evaluating muscle morphology, yet its dynamic reliability in cervical muscles requires further validation. This study examined the test–retest reliability of longus colli muscle assessment using ultrasound during the craniocervical flexion test (CCFT).Methods Forty healthy participants (21 men, 19 women; mean age 21.6 ± 1.7 years, range 18–35) underwent two sessions of transverse ultrasound evaluation of the longus colli at the C5–C6 level during CCFT at rest (20 mmHg) and during contraction at 22 mmHg, 24 mmHg, and maximal acceptable effort (≤30 mmHg).Results Cross-sectional area (CSA) of the longus colli demonstrated good reliability (ICC = 0.80–0.86). Dimensions showed moderate to good reliability (ICC = 0.50–0.76 and 0.12–0.76). CSA changes across CCFT stages exhibited poor reliability (ICC = 0.24–0.37)Conclusions CSA demonstrates acceptable test-retest reliability for assessing longus colli during the CCFT in healthy young adults. Further research is needed to establish inter-rater reliability, examine test-retest reliability over longer intervals, and determine whether these findings are applicable to clinical populations with neck pain.