The Effect of Hand-held Vibrating Tools on Muscle Activity and Grip Strength

Many vibration-exposed workers have been found to suffer from muscle fatigue and decreased grip strength. Therefore in order to quantify and determine safe levels of human exposure to vibration, measurements and analysis of significance vibration factors are necessary. There are three main objectives in this study. The first one is to investigate the characteristics of vibration factors (vibration level and exposure duration) produced by vibrating tools that affect to muscle activity. The second objective is to analyze the effects of vibration exposure on muscle activity and grip strength and the third one is to determine the relationship between objective and subjective measurements for muscle activity. The study is a laboratory experimental study which was involved eighteen subjects (nine male and nine female). The experiments were performed with two exposure times, five and 15 minutes. Subjects were required to drill wood specimen using an electric drill and a bench drill. Electromyography (EMG) and Vernier LabPro with a three axis accelerometer and a hand dynamometer were used in the experiment. Vibration level that produced during drilling with bench drill and electric drill for five and 15 minutes were 10.24 m/s, 10.45 m/s, 10.38 m/s and 10.69 m/s respectively. The most affected muscle was found to be the right extensor carpi radials. The results of bench and electric drill showed that right extensor carpi radialis muscle had the highest percentage of Maximum Voluntary Contraction (MVC) with values of 12.43%MVC and 23.50%MVC, respectively. Subjective measurement results showed similar results with objective measurement. It indicated that lower arm part is the most affected area by vibration factors compared to the other body part. Drilling wood material/specimen with an electric drill resulted in higher vibration levels (3.01%), percentage decrease ratio (29.22%) and percentage MVC (88.38%) than using a bench drill for the extensor carpi radialis muscle. The findings of the study indicated that as the level of vibration increases the muscular activity and the percentage decrease ratio of grip strength also increases. Thus, vibration may be a contributory factor to arm disorders such as muscle fatigue among operators with power hand tool.