LAUSR

BACKGROUND Neck pain is one of the most common musculoskeletal complaints. Evidence suggests that increased activities of neck and trunk muscles are one of the mechanisms related to neck pain. Jaw clenching and sitting posture may modulate the muscle activity in neck and trunk muscles during typing. OBJECTIVE The present study aimed to assess the effects of different postural positions and clenching conditions on neck and trunk muscle activities. METHODS Thirteen healthy adults (39.8 ± 5.0 years) performed computer typing tasks in four conditions (two postural positions [upright vs. slouched] and two jaw clenching conditions [clenching vs. non-clenching]). Integrated surface electromyography (iEMG) was measured in sternocleidomastoid (SCM), upper trapezius (uTP), and middle trapezius (mTP) muscles and compared between conditions. Friedman and Wilcoxon signed-rank tests with Bonferroni corrections were used to estimate the condition-specific differences in the iEMG data. The statistical significance level was set at 5%. RESULTS In both postural positions, iEMGSCM was significantly greater under the jaw clenching than under the non-clenching condition (χ2 = 21.700, p < 0.01). Under both jaw clenching conditions, iEMGuTP was significantly greater in the slouched than in the upright postural position (χ2 = 23.182, p < 0.01). No significant differences in iEMGmTP were seen across conditions (χ2 = 5.018, p = 0.10). CONCLUSION Sitting posture and jaw clenching appear to influence activities of different muscles.