Calibrating Borg scale ratings of hand force exertion

A study was conducted to assess the efficacy of calibrating subjective worker ratings of hand exertions to reduce error in estimates of applied force. Twenty volunteer subjects applied pinch and power grip forces corresponding to their perceptions of different Borg CR-10 scale levels using both "grip-to-scale" and "guided-grip" procedures. These data were used separately to define relationships between scale ratings and actual force application. Two gripping tasks were performed and corresponding subjective hand force ratings were calibrated using the grip-to-scale calibration data. Results showed that the mean estimation error for a 44.5 N (10 lb) power grip task was significantly reduced from 142.8 (+/-69.0) to 62.3 (+/-58.3) N. The guided-grip calibration method also significantly reduced rating error for the power grip task, however the estimates were biased toward zero. Neither calibration procedure improved rating accuracy of an 8.9 N (2 lb) pinch grip task. The study results indicate that calibration of hand force ratings using the grip-to-scale procedure may improve the accuracy of hand exertion measurements using the Borg CR-10 scale.