[Pinch assessing in bio mechanical analysis: methodological and applicative aspects dealt by using the new P force...

Definition and significance of term pinch and related force exerted are still open outside the ergonomic field of interest too. The lack of consent appears relevant in upper limb biomechanical risk assessment. Aim of this study is to focus methodological aspects and applications of pinch, analyzing four actions by a new portable instrument able to measure strain exertion during pinch action.

A portable apparatus named P-forceMet, produced by OT bioelettronics, Turin (Italy) had been used. It measures the force generated by voluntary muscle contraction both in maximal condition (MCV) and in specific working conditions (Spontaneous Force, SF). We examined four groups of 27 subjects exerting forces of different entity required in 4 technical actions: tightening bolts, writing with a pen, use a brush to spread sealer, wiring cables. The workers were asked to exert the MCV and value was registered to be compared with force simulated on the instruments taking into account the specific experienced action. Data from force analysis by Borg scale and data about upper limb disorders had also collected, as well as the results of risk assessment by checklist OCRA application.

Comparing MCV and SF we demonstrated different levels of measured forces: from 2-3% when using the pen to write to 8-12% for cabling and brushing activities to 31% for manual tightening. These results were in good agreement with evaluations by Borg scale, while risk assessment by check list OCRA were discordant (sealing and cable wiring were sometimes at level of mild to medium risk mainly due to posture evaluation of pinch). Workers engaged in writing, sealing and cabling did not suggest disorders to wrist-hand.

Actions with pinch are numerous in working activities and if defined "at risk" only because they require posture of opposition of the first two fingers, we could not classify correctly to the real bio mechanical overload. This study carried out using an instruments able to measure the force exerted during pinch operations demonstrates that the force (and then of possible strain) is diferent in the four activities. It confirms the importance of critical evaluation of different hazards and of their interaction in causing the functional or organic disorder. In our case a remarkable difference of force was demonstrated by instrument p-force in actions involving the same hazard related to posture. Further investigation appears to be necessary to eliminate the residual subjective component of this force measurement method due to the necessity of simulating the force requested by specific action.