Back muscle activity while operating a vehicle

Abstract

Research and/or Engineering Questions/Objective: Low Back Disorder (LBD) is common in automobile drivers and prominent in truck drivers. Rate of LBD was found to be 40% among all truck drivers and 65% among professional drivers with 15 years behind the wheel. Whole-body vibration (WBV) has repeatedly been identified as a risk factor for LBD. Sitting in awkward postures while exposed to vibration increases the rate of LBD fourfold. However, the injury mechanisms that link vibration to LBD are still not completely understood. The long term purposes of our study are to determine muscle contribution to associated LBD while operating a vehicle. The specific aim of this study was to determine back muscle activity in response to lumbar inclination angles and vibrations from driving on different road surfaces. Methodology: The Surface Electromyography (sEMG) of latissimus dorsi and lumbar erector spinae muscles were recorded from eight adults (seven male, one female, age from 18-45) using Biopac Data Acquisition System (Model MP30, Biopac Systems Inc, Goleta, CA) and analysed using Acqknowledge software (Ver. 4.2). Two accelerometers (Model TSD109F, Biopac Systems Inc, Goleta, CA) were attached to the driver waist and vehicle floor respectively. sEMG and vibration data was recorded simultaneously under various operating conditions including: sitting with several lumbar inclination angles, engine idling, and driving on smooth, pebble, potholed roads, and freeway. Correlation between sEMG (normalized to individual Maximum Voluntary Contraction (MVC)) and vibration measures (mean, median, peak frequency; Root Mean Square (RMS); and Power (G2/Hz) was analyzed. ANOVA, Kruskal-Wallis, correlation and regression, and other statistical methods were used to analyse EMG and vibration variables under different operating conditions using SPSS software with p < 0.05 considered as a significant level. Results: A quadratic correlation between normalized sEMG (%MVC) and lumbar inclination angle was found. Each driver had a lumbar inclination angle that elicited only a lowest %MVC. This angle ranked from 0 to 23° (13.14 ± 4.14, Mean ± SEM). The inclination angle from the most desirable driving posture was not correlated with the inclination angle with the lowest %MVC (x2 test, p = 0.304). Driving on potholed road elicited a highest %MVC and highest acceleration power (G2/Hz) (ANOVA, p < 0.05). The highest %MVC was 18% in potholed road driving. The vibration acceleration power (G2/Hz) had a linear correlation with %MVC EMG activity (Pearson test, p < 0.00). Mean, median, or peak frequency of vibration did not have a linear correlation with EMG Power (V2/Hz) or RMS (Pearson test, p > 0.05). The vibration frequency, RMS, and power of vibration (G 2/Hz) recorded from lumbar region were lower than that recorded from the vehicle floor (Paired t test, p = 0.000). Limitations of this study: The limitation of this study is that the road testing time period was shorter than the realistic driving conditions which have a longer time period. Muscle fatigue or secondary pain over the long driving time period was not determined in this study. What does the paper offer that is new in the field including in comparison to other work by the authors: Currently, most research uses Root Mean Square (RMS) to measure the magnitude of and intensity of vibration, as well as EMG response. This study demonstrated that magnitude of vibration (G 2/Hz) corresponded to power (V2/Hz) of EMG better than other EMG measures including RMS and frequency analysis. In addition, various vibration curves under different operating conditions were obtained in this study; these vibration curves are required for input of vibration loading conditions during finite element analysis fatigue analysis. Conclusions: The probability for driver to develop muscle fatigue is higher when driving on potholed road because intermittent muscle contractions were more than 10% MVC under this condition. Sitting posture has effects on muscle activity. Driver's comfort did not show a direct correlation to the lumbar inclination angle that elicited the lowest %MVC. The seat may absorb some of the vibration energy from the vehicle, reducing the intensity of vibration transferred to the human body. In this study, power (G2/Hz in vibration and V2/Hz in EMG) was more sensitive and specific for analysis of the magnitude of vibration and corresponding EMGs. © Springer-Verlag 2013.