Comparison of three psychophysical techniques to establish maximum acceptable torques of repetitive ulnar deviation

This study represents a continuation of a series of psychophysical studies on repetitive motions of the wrist and hand conducted at the Liberty Mutual Research Center for Safety and Health. The purpose of this study was to compare maximum acceptable torques of ulnar deviation determined after a replicated training protocol from an earlier single-movement study of ulnar deviation with maximum acceptable torques of ulnar deviation from both the previous single-movement study and two multi-movement studies. A psychophysical methodology was used in which the subject adjusted the resistance on the handle, and the experimenter manipulated or controlled all other variables. After the 1-week training protocol, 14 subjects performed a ulnar deviation task for six 7-hour work days, 2 days at each repetition rate of 15, 20 and 25 motions per minute. The subjects were instructed to work as if they were on an incentive basis, getting paid for the amount of work they performed. The subjects recorded symptoms during the last 5 minutes of each hour. By replicating the training protocol of a previous single-movement study, the results of this experiment revealed that maximum acceptable torque of ulnar deviation in this study (1.65Nm or 22% of maximum isometric torque) approached a similar level of torque to that reported in the previous single-movement study for a frequency of 15 per minute. However, when further accommodation was shortened in the 20 and 25 per minute conditions, the acceptable torque levels departed from the previous single-movement study and approached lower levels achieved in the multiple-movement studies which had shorter accommodation times for each movement. These results suggests that the maximum acceptable torque determined through psychophysical methods is dependent upon accommodation time in the protocol and that effect of experimental design (single- vs multi-movement) needs to be further explored.

[1]  W Karwowski,et al.  Beyond psychophysics: the need for a cognitive engineering approach to setting limits in manual lifting tasks. , 1999, Ergonomics.

[2]  M W Riley,et al.  The Effects of Handle Shape and Size on Exerted Forces , 1986, Human factors.

[3]  P G Dempsey,et al.  Ergonomics investigation of retail ice cream operations. , 2000, Applied ergonomics.

[4]  S H Snook,et al.  Psychophysical studies of repetitive wrist flexion and extension. , 1995, Ergonomics.

[5]  D B Chaffin,et al.  Ergonomics guide for the assessment of human static strength. , 1975, American Industrial Hygiene Association journal.

[6]  S H Snook,et al.  Psychophysical study of six hand movements , 2001, Ergonomics.

[7]  Stover H. Snook,et al.  Maximum acceptable forces for repetitive wrist extension with a pinch grip , 1999 .

[8]  S H Snook,et al.  Maximum acceptable forces for repetitive ulnar deviation of the wrist. , 1997, American Industrial Hygiene Association journal.

[9]  G. J. Gouw,et al.  A study of hand grip pressure distribution and EMG of finger flexor muscles under dynamic loads. , 1995, Ergonomics.

[10]  Vincent M Ciriello,et al.  Maximal acceptable torques of highly repetitive screw driving, ulnar deviation, and handgrip tasks for 7-hour workdays. , 2002, AIHA journal : a journal for the science of occupational and environmental health and safety.

[11]  R Kadefors,et al.  Tool design, user characteristics and performance: a case study on plate-shears. , 1993, Applied ergonomics.

[12]  Raymond W. McGorry,et al.  Experimental appraisal of a manual task evaluator , 2000 .

[13]  S H Snook,et al.  Psychophysical considerations in permissible loads. , 1985, Ergonomics.

[14]  T K Courtney,et al.  Length of disability and cost of work-related musculoskeletal disorders of the upper extremity. , 1998, Journal of occupational and environmental medicine.