Upper extremity strength: Normative reference data among uninjured employees

Abstract

BACKGROUND: Extremity strength testing is used to determine the ability of industrial employees to perform a physically demanding occupation safely, evaluate post-injury impairment, and monitor return to function after injury. There is an unmet clinical need for a robust and granular source of normative reference values to serve as a resource for baseline data on upper extremity isometric strength. OBJECTIVE: Develop normative reference data for upper extremity strength among industrial employees and investigate associations between strength and physical job demands. METHODS: Upper extremity strength data from 107,102 industrial employees were collected post-hire. In this study, isometric tests for pinch; hand grip; wrist pronation and supination; and flexion of the wrist, elbow, and shoulder strength were retrospectively analyzed in relationship to sex, age, and job level. Associations between strength scores and five levels of work, defined the United States Department of Labor’s Dictionary of Occupational Titles by level of physical difficulty (1–5), were determined. RESULTS: Higher strength scores were positively associated with more physically demanding job levels (P < 0.001), and there was a progressive increase in strength scores with increased physical job demands for both sexes (P = 0.0002). All strength scores differed significantly by decade of age (P < 0.001). All scores except for pinch strength demonstrated a moderate or high positive correlation with job level (r≥0.50). CONCLUSIONS: The normative reference upper extremity strength data collected in this study for industrial employees may be useful for evaluating rehabilitation and recovery following injury or illness. In order to utilize normalized strength data as a post-injury reference, it is important to consider job level in addition to age and sex, as these variables are highly correlated with baseline upper extremity strength.