Effect of neck-specific exercises on trapezius muscle function in chronic whiplash-associated disorders: a longitudinal case–control study using ultrasound and speckle-tracking analyses

Neck-specific exercises can improve the function of deep neck muscles in individuals with chronic whiplash-associated disorders (WAD), but it remains unclear whether these exercises also enhance the function of superficial neck muscles. The superficial trapezius muscle is frequently painful in WAD, yet effective conservative treatments are lacking. In total, 34 individuals with WAD and 34 healthy controls were recruited to assess upper trapezius function. Five participants from each group were excluded due to blurry ultrasound image or extreme outliers, resulting in 29 participants per group. Of the participants with WAD, 25 were reassessed after completing a 3-month neck-specific exercise program. Real-time, non-invasive ultrasound with speckle tracking was used to measure muscle deformation, enabling the detecting of subtle functional changes in the trapezius muscle that might not be captured by other methods. Participants rated neck disability, neck pain, and muscle fatigue at baseline and at 3-month follow-up (WAD group only). A significant group difference in trapezius deformation was observed at baseline (F[1,55] = 5.6, p = 0.022, ηp² = 0.09), with larger deformation in the WAD group. After three months, no significant group difference remained (F[1,47] = 2.3, p = 0.137, ηp² = 0.05). However, no significant within-group changes in deformation were found in the WAD group. In contrast, neck disability, neck pain, and muscle fatigue improved significantly following the intervention indicating a clear clinical benefit of the exercises. These findings suggest improved deformation of trapezius through neck-specific exercises, but the non-significant within-group change in muscle deformation warrants cautious interpretation. Trial registration number and date of registration: The protocol was registered before data collection started at Clinicaltrial.gov (Protocol ID: NCT03664934, first posted date 11/09/2018).