Neck muscle fatigue alters the cervical flexion relaxation ratio in sub-clinical neck pain patients

- Fatigue effects on cervical flexion relaxation were compared in neck pain vs control.
- The flexion relaxation ratio decreased significantly for controls following fatigue.
- The ratio increased slightly for sub-clinical neck pain patients following fatigue.
- EMG onset and offset angles decreased significantly for both groups after fatigue.
- Neck pain impacts the ability of the neuromuscular system to adapt to fatigue.

BackgroundThe cervical flexion relaxation ratio is lower in neck pain patients compared to healthy controls. Fatigue modulates the onset and offset angles of the silent period in both the lumbar and cervical spine in healthy individuals; however, this response has not been studied with neck pain patients. The purpose of this study was to determine if cervical extensor fatigue would alter the parameters of the cervical flexion relaxation more in a neck pain group than a healthy control group.MethodsThirteen healthy and twelve neck pain patients participated. Cervical extensor activity was examined bilaterally and kinematics of the neck and head were collected. An isometric, repetitive neck extension task at 70% of maximum elicited fatigue. Participants performed 3 trials of maximal cervical flexion both pre and post fatigue.FindingsThe healthy controls and neck pain groups fatigued after 56 (41) and 39 (31) repetitions, respectively. There was a significant interaction effect for the flexion relaxation ratio between the control and neck pain groups from pre to post fatigue trials (F1,96 = 22.67, P = 0.0001), but not for onset and offset angles (F1, 96 = 0.017, P = 0.897), although the onset and offset angles did decrease significantly for both groups following fatigue (F1,96 = 9.26, P = 0.002).InterpretationIndividuals with mild to moderate neck pain have significant differences in their neuromuscular control relative to controls, experienced myoelectric fatigue with fewer repetitions in a shorter time, had a lower cervical flexion relaxation ratio at baseline and had an inability to decrease this ratio further in response to fatigue.