Post fatigue changes in the stability of cervical spine.

摘要

Musculoskeletal disorders (MSDs) of the neck or cervical spine are a common problem in the modern workforce. An annual prevalence of 30% to 50% for neck pain among the general adult population was reported by the Task Force of Bone and Joint Decade on Neck Pain. Physical work demands, such as sustained static postures, sub-maximal repetitive arm exertions, and forceful arm exertions are consistently identified as possible risk factors for cervical spine MSDs. Most of these exertions induce neck muscle fatigue which may affect the stability of the cervical spine. A less stable spine can be both a cause and consequence of spinal pain. The effect of muscle fatigue on the stability of the cervical spine is currently not well understood. The objective in this study was to quantify the post-fatigue changes and recovery of the cervical spine's stability. Specifically, the flexion-relaxation phenomenon (FRP) and sudden perturbations (SP) procedures were used to study the variables that influence the stability of the cervical spine. The FRP explains the synergistic load sharing between the muscles and viscoelastic elements (ligaments, discs, capsules, and fascia). The SP protocol allows quantification of the muscle reflex responses necessary to maintain spinal stability.;Twenty human participants (10 male and 10 female) were recruited for data collection and the Sorenson protocol was utilized to induce neck muscle fatigue. Surface electromyography and optical motion capture systems were used to measure neck muscle activation and head-neck posture, respectively. A six degree of freedom force torque sensor was used to record the force profile data during the SP procedure.;Localized muscle fatigue significantly reduced the flexion-relaxation ratio from 4.88 +/- 0.81 pre-fatigue to 3.33 +/- 0.57 post-fatigue. A post-fatigue decrease was also observed in the onset and offset angles by about 16% and 5%, respectively, resulting in an expansion of the myoelectric silence period by 17.2%. The intrinsic stiffness of cervical spine was reduced from 975.75 +/- 85.87 Kg/sec2 pre-fatigue to 826.31 +/- 90.76 Kg/sec2 post-fatigue. The corresponding change in the effective stiffness was from 1404.64 +/- 122.31 Kg/sec 2 to 1086.53 +/- 123.73 Kg/sec2. The temporal parameters related to the reflexive response of the neck extensors were also affected by fatigue. Onset delay, time to peak and peak to peak values increased from 92.81 +/- 21.06 to 127.07 +/- 30.45 msec, 231.08 +/- 39.55 to 325.54 +/- 49.99 msec, and 89.36 +/- 36.40 to 178.22 +/- 49.28 msec, respectively, post-fatigue. A slight but non-significant decrease in the reflex gain and reflex amplitude was also observed post-fatigue.;Post-fatigue recovery of the FRP and SP parameters was measured during the rest period at 15, 30, 45 and 60 minutes. Majority of the parameters showed close to full recovery in the first 30 minutes. A recovery of about 79% to 95% was observed during the first 15 minutes and during the next 15 minutes a recovery of about 5% to 11% was observed.