Reliability and Validity Assessment of the Hand Activity Level Threshold Limit Value and Strain Index Using Expert Ratings of Mono-Task Jobs

Abstract

This study evaluated two subjective assessment methods for physical work-related musculoskeletal disorder (WMSD) risk factors. A total of 567 participants from 12 companies in the manufacturing and health care industries were evaluated using the hand activity level (HAL) threshold limit value (TLV) and the Strain Index. Inter-rater reliability comparisons were performed on 125 selected cyclic tasks, with one novice and three experienced raters. Predictive validity was assessed by evaluation of relationships between measured exposure parameters and diagnosed WMSDs of the hand/wrist and elbow. HAL hand repetition ratings had a Spearman r value of 0.65 and a kappa value of 0.44 between raters. Subjective force (0–10 scale) estimates had a Spearman r = 0.28 and were not significantly different between raters (p > .05). The rating comparison for the four subjective components of the Strain Index had Spearman r correlations of 0.37–0.62 and kappa values of 0.25–0.44. The Strain Index and HAL TLV agreed on exposure categorization 56% of the time. Logistic regression showed, after adjustment for age, gender, and body mass index, that higher peak hand force estimates (odds ratio [OR] 1.14, confidence interval (CI) 1.02–1.27), most common force estimates (OR 1.14, CI 1.02–1.28), hand/wrist posture rating (OR 1.71, CI 1.15–2.56), and Strain Index scores ≥ 7 (OR 1.82, CI 1.04–3.18) were associated with distal upper extremity disorders in the dominant hand. HAL repetition ratings ≥ 4 (OR 2.81, CI 1.40–5.62) and hand/wrist posture ratings (OR 1.59, CI 1.01–2.49) were associated with disorders in the nondominant hand. These findings show moderate to good inter-rater agreement and significant relationships to health outcomes for the identified measures.