Summary

Exposure to vibration is a significant issue in the prevention of musculoskeletal disorders of the upper limbs. Hand-arm vibration is specifically recognized as the cause of vibration syndrome, a disease of the fingers and hand with vascular, musculoskeletal and neurosensory components. Long-term and high-intensity vibration can hasten the onset of symptoms.

This study, which included two components, explored variables that can affect the transmission of vibration to the upper limbs as well as muscle load. Twelve participants divided into two somatotypes (six ectomorphs and six mesomorphs) participated in each component. A vibrator was used to control specific variables and expose the subjects to various combinations of vibration amplitude (2.5 m/s2, 5 m/s2 and 10 m/s2) and frequency (20, 40 and 65 Hz) for the two components. The subjects were asked to hold the vibrator’s instrumented handle for ten seconds.

The purpose of this study was to  measure the transmission of vibration and muscle load based on different biomechanical variables. For the first component, these variables were gripping force (25 N, 50 N and 100 N) and wrist deviation (neutral, abduction and adduction). The second component evaluated the effect of moments of force (1. 2 and 4 Nm) exerted in the wrist and different thrusting forces (0. 20 and 40 N) exerted on the wrist.

Electromyography was used to measure the myoelectric activity of several major muscles. In addition, two triaxial accelerometers attached to the wrist and elbow were used to determine vibration transmission amplitude based on the different variables studied.
The findings indicated that stronger gripping force increased the transmission of vibration to the upper limb. Moreover, the ectomorph subjects tended to transmit more vibration and make greater use of certain muscles (extensor digitorum communis). An increase in moment of force and thrusting force generally led to greater vibration transmission and muscle demand. The vibration variables indicated the presence of a significant but minor tonic vibratory reflex. Lastly, it seems that the combination of high amplitude (10 m/s2) and low frequency (20 Hz) of vibration was the one with the highest upper limb muscle constraints.