Effects of Cervical Flexion on the Flexion-relaxation Ratio during Smartphone Use

[Purpose] The purpose of this study was to measure the cervical flexion-relaxation ratio(FRR) and intensity of neck pain and identify the differences according to posturesadopted while using smartphones. [Subjects] Fifteen healthy adults with no neck pain,spinal trauma, or history cervical surgery participated in this study. [Methods] Theactivity of the cervical erector spinae muscle was recorded while performing astandardized cervical flexion-extension movement in three phases (flexion, sustained fullflexion, extension). And neck pain intensity was recorded using a visual analog scale(VAS) with values between 0 and 10. Postures held while using a smartphone aredistinguished between desk postures and lap postures. The FRR was calculated by dividingthe maximal muscle activation during the extension phase by average activation during thecomplete flexion phase. [Results] No significant differences were found in the FRR betweendesk posture, lap posture, and baseline, though the intensity of the neck pain increasedin the lap posture. [Conclusion] The FRR could be a significant criterion of neuromuscularimpairment in chronic neck pain or lumbar pain patients, but it is impossible todistinguish neck pain that is caused by performing task for a short time. Prolonged lapposture might cause neck pain, so the use of smartphones for a long time in this postureshould be avoided.Key words: Smartphone, Cervical flexion-relaxation ratio, Electromyography