Effects of vibration on muscles in the neck and upper limbs : with focus on occupational terrain vehicle drivers

Sammanfattning: Introduction: Occupational drivers of terrain vehicles are exposed to several risk factors associated with musculoskeletal symptoms in the lower back as well as in the neck and upper limbs. Vibration has been suggested to be a main risk factor. These drivers are exposed to both whole-body vibration (WBV) and hand-arm vibration (HAV). Aim: This study establishes the association between driving terrain vehicles and musculoskeletal disorders (MSDs) in the neck and upper limbs as well as hand-arm vibration syndrome (HAVS). In addition, this study examines the effect on muscles in the neck and upper limbs of the type of vibration exposure that occurs in occupational driving of terrain vehicles. Methods and results: In Paper I, a cross-sectional questionnaire study on occupational drivers of terrain vehicles, increased Prevalence Odds Ratios (POR) were found for numbness, sensation of cold and white fingers (POR 1.5-3.9) and for MSDs in the neck (POR 2.1-3.9), shoulder (POR 1.8-2.6) and wrist (POR 1.7-2.6). For the shoulders, neck and elbow, there appears to be a pattern of increased odds with increasing exposure time. In Paper II, an experimental study on the trapezius muscle, which included 20 men and 17 women, the mean frequency of the electromyography signal (EMGMNF) decreased significantly more in a three minute sub-maximal contraction without vibration (-3.71Hz and -4.37Hz) compared to with induced vibration (-3.54Hz and -1.48Hz). In Paper III, a higher initial increase of the mean of the root-mean-square of the electromyography signal (EMGRMS) was seen in a three minute sub-maximal contraction with vibration exposure compared to without vibration (0.096% vs. 0.045%). There was a larger mean EMGMNF decrease for NV compared to V in the total three minutes, and a larger decrease also in the first time period was seen for the NV compared to V. A small gender effect was also noticed. In Paper IV, the combination of HAV and WBV was studied in laboratory settings and resulted in a higher trapezius EMGRMS compared to the HAV and WBV separately. Conclusion: Occupational drivers of terrain vehicles are likely to experience symptoms related to HAVS and musculoskeletal symptoms in the neck and upper limbs. Local vibration does not seem to have any negative acute effects on trapezius muscle fatigue. Vibration exposure seems to cause an initial increase in muscle activity in the trapezius that could be related to recruitment on new motor-units. A combination of HAV and WBV causes a larger muscular demand on the trapezius muscle.