Kinematic and electromyographic parameters of the cervical flexion–relaxation phenomenon: The effect of trunk positioning

Abstract

Background The cervical flexion–relaxation phenomenon (FRP) is a neck extensor myoelectric “silence” that occurs during complete cervical flexion. The aim of this study was to assess the presence of this phenomenon in the cervical region and to explore the kinematics and EMG parameters in two different experimental conditions. Patients and methods Nineteen young healthy adults (22.2 ± 2.4 years), without any cervical pain history, participated in this study and performed each of the experimental conditions. They had to accomplish a cervical flexion from a neutral seated position and from a 45° forward leaning seated position. Neck kinematics was assessed using a kinematic capture device in order to assess onset and cessation angle of the PFR. Cervical paraspinal and trapezius muscles EMG activities were also recorded. All data were compared in order to assess the differences between the two experimental conditions. Results Eighteen of the nineteen subjects showed a FRP. The phenomenon appears between 72.6 and 76.3% of maximal cervical flexion and disappears during the return to neutral position between 91.9 and 93.1% of maximal cervical flexion. The FRP was observed, at least unilaterally, in 84.2% (67.4% bilaterally) of tasks without forward bending of trunk, and 90.5% (79.0% bilaterally) of tasks with 45° forward bending of trunk. A significant increase in the flexion–relaxation ratio was observed in the 45° forward leaning condition. No significant difference could be observed between the two experimental conditions for the kinematics parameters. Conclusion The results of the present study indicate that cervical spine flexion in healthy subjects is characterized by a flexion–relaxation response. Moreover, the results indicate that trunk inclination might facilitate the evaluation of the cervical FRP.