RISK ASSESSMENT OF REPETITIVE TASKS: A COMPARATIVE ANALYSIS AMONG DIFFERENT METHODS TO UPDATE THE MAXIMUM FREQUENCY ALLOWED

A comparison in terms of the maximum frequency of movement allowed in the no-risk area, when the force and the duty cycle, was made among some of the most used methods for assessing distal upper extremity (DUE) work-related musculoskeletal disorders (WMSDs). The methods investigated are as follows: Strain Index (SI) (1995 version), Revised Strain Index (RSI), Occupational Repetitive Action (OCRA) Index and American Conference of Governmental Industrial Hygienists Threshold Limit Values ACGIH (TLV). Even though the RSI algorithm introduces important modifications compared to the previous version, marked differences still remain among those methods analyzed. The RSI provides similar results to the OCRA Index and ACGIH (TLV) in less than 1/3 of the overall pre-set combinations of force (measured in Borg Scale (BS)) and duty cycle (DC). Some of the highlights are as follows: the ACGIH (TLV) method allows 6 exertions per second in the net time of the cycle, while the RSI less than 1 (0.86), in the hypothesis of BS = 1 and DC = 60%; in the same conditions, but for a DC = 100%, the ACGIH (TLV) method allows almost 2 exertions per second (1.7), while the RSI and the OCRA Index do not consider any frequency of movement as ‘safe’ in this circumstance; in the same conditions as above, but when DC = 20% and BS = 5, the RSI method allows less than 0.5 (0.31) exertions per second, while using the OCRA Index it is possible to stay in the ‘safe’ area even if the number of exertions per second is over 4 (4.68). What can be considered noteworthy, beyond the relative differences among the results, is that in some particular circumstances the methods seem to start from different boundary conditions. A greater amount of epidemiological data would be desirable in order to better define t