Montreal, April 10, 2014 - Workers using vibrating tools are subject to effects that progress slowly and may result in musculoskeletal injuries or disorders in their upper limbs. For that reason, a research team set about measuring, among other things, the effects of factors such as the wrist deviation and grip strength exerted on tool handles, on vibration transmission and on muscle load.

To this end, they recruited twelve right-handed subjects (volunteers) and divided them into two groups according to their body type: the ectomorphic type (thin frame with lean muscle mass and little body fat), and the mesomorphic type (solid frame with considerable muscle mass and little fat). Each type was tested on a laboratory vibration generator to measure muscle load and vibration transfer to their upper limbs.

Results

Using electromyography and accelerometers, the researchers demonstrated, among other things, that the greater the strength of the grip on the tool, the greater the transmission of the vibration. They also found that there was greater transmission of vibration to the wrists and elbows of the ectomorphic subjects, and that some of these subjects’ muscles were more stressed than those of the mesomorphic subjects. The study also examined vibration-related parameters, and established that tools whose vibration amplitude was high (10 m/s2), and that emitted low frequencies (20 Hz), generated greater muscle stress.

"This study is very useful, because the studies that will follow on from it will serve as benchmarks for manufacturers of impact tools and hammer tools. For example, one would need only to design lighter tools whose centre of mass was closer to the hand to reduce the grip force required to use them and thus reduce the vibration transmitted to the muscles of the upper limbs. Manufacturers could help prevent musculoskeletal disorders (MSDs) by changing the amplitude of vibration of their tools and making sure that their operating frequencies were more appropriate", said lead author, Denis Marchand, Professor in the Department of Anthropokinetics at UQAM.

The study, entitled Vibrating Tools – Biomechanical and Sensorimotor Parameters Affecting the Biodynamic Response of the Hand-Arm System, has been published by the Institut de recherche Robert-Sauvé en santé et en sécurité du travail (IRSST), and may be consulted free of charge at http://www.irsst.qc.ca/media/documents/PubIRSST/R-815.pdf (French only).

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Source
Jacques Millette
Head of Public Affairs
IRSST