A decreased ability to relax between repetitive muscle contractions in patients with chronic symptoms after whiplash trauma of the neck

Objectives: The aim was to investigate if patients with common chronic symptoms after whiplash trauma had an inability to relax certain neck and shoulder muscles in pauses between repetitive shoulder forward flexions. Methods: The control group [27 clinically healthy females] and the patient group [22 female patients with chronic symptoms after whiplash trauma] performed maximum isokinetic shoulder flexions [100 contractions scheduled]. Surface-electromyography [EMG] was obtained from four neck/shoulder muscles. Peak torque and the signal amplitude ratio [SAR] of each contraction were determined. The SAR was calculated as the ratio [%] between root mean square [RMS] of the EMG of the passive extension and the RMS of the active flexion. The subjects rated their perceived fatigue of the shoulder flexors throughout the test. Results: The majority of the patient group was not able to perform the number of contractions scheduled. Significantly higher SAR of trapezius two portions and infraspinatus for the patient group than for the control group were found. Conclusions: The results confirm the clinical experience of increased stiffness/tension in patients with chronic symptoms after whiplash trauma. Damage to sensory structures in ligaments and joints causing alterations in the regulation of muscle stiffness around the joints and/or secondary effects of chronic pain might be responsible for the increased tension.