The Revised Strain Index: an improved upper extremity exposure assessment model.

Area of Science:

• Occupational Health
• Ergonomics
• Biomechanics

Background:

• The 1995 Strain Index (SI) is a model for assessing physical exposure in distal upper extremity (DUE) tasks.
• Existing models may lack precision in differentiating risk levels for certain task parameters.

Purpose of the Study:

• To introduce and evaluate the Revised Strain Index (RSI) as an improved model for DUE physical exposure assessment.
• To compare the risk predictions of the RSI against the 1995 SI.

Main Methods:

• The Revised Strain Index (RSI) incorporates continuous multipliers for exertion intensity, frequency, and duration, along with hand/wrist posture and daily task duration.
• A simulation involving 13,944 tasks was conducted to compare RSI and 1995 SI predictions.
• The models were evaluated based on their agreement and disagreement in risk predictions across different score ranges.

Main Results:

• The RSI and 1995 SI demonstrated good agreement for low (≤3) and high (>13.5) risk scores.
• Significant disagreements were observed for intermediate risk scores (scores >3 and ≤13.5), where the RSI showed greater discrimination.
• The RSI effectively differentiated between 'safe' and 'hazardous' tasks across various force, repetition, and duty cycle combinations.

Conclusions:

• The Revised Strain Index (RSI) represents a substantial improvement over the 1995 SI for DUE task analysis.
• The RSI is a valuable tool for designing and analyzing tasks to mitigate the risk of musculoskeletal injuries.
• The RSI is applicable to a broad spectrum of tasks, including those with low force and high repetition, such as keyboard use.