Immediate local fatigue effects on sensorimotor cervical activity and proprioception in individuals with and without neck pain history
Background: Fatigue may perpetuate a vicious cycle of cervical muscle dysfunction and altered proprioception. This study investigated fatigue effects on deep cervical muscle activity measured as tissue stiffness and superficial cervical muscle electromyography (EMG) activity during the deep neck flexor endurance (DNFE) test and neck retraction in a four-point kneeling position in individuals with and without history of neck pain (hxNP). The secondary purpose was to investigate fatigue effects on joint position sense (JPS) errors in individuals with and without a hxNP. Methods: Thirty-four subjects (hxNP=17, healthy controls=17) between the ages of 18-55 years completed the study. Deep cervical muscle shear wave elastography (SWE) measurements and superficial cervical muscle electromyography were recorded during the DNFE test, neck retraction during a four-point kneeling position, and JPS error testing prior to and immediately following fatigue. Within and between-group comparisons were analyzed with mixed ANOVAs for fatigue effects on cervical muscle SWE stiffness measures and EMG activity, and JPS errors in individuals with and without hxNP. Results: The hxNP group demonstrated reduced deep cervical flexor and extensor SWE stiffness measures compared to healthy controls prior to fatigue. In addition, both groups demonstrated decreased deep cervical flexor (p<.001) and extensors(p<.001) SWE stiffness measures following fatigue. The superficial cervical flexor (p>0.05) remained unchanged following fatigue, while superficial extensors (p=.017) EMG activity reduced following fatigue. The JPS errors (p>.05) were found to be similar in both groups regardless of the local muscle fatigue condition. Conclusion: Overall, the hxNP groups exhibited decreased deep cervical flexor and extensor SWE stiffness measures compared to healthy controls prior to fatigue. Fatigue affected both groups similarly irrespective of cervical flexor and extensor fatigue protocol. The superficial flexors and extensors EMG activity exhibited inconsistent muscle activation pattern following fatigue. Further, the JPS errors remained unaffected with fatigue. It seems that fatigue might not play a significant role in the high recurrence and chronic symptoms in neck pain patients.