Exploring the Use of Biomechanical Metrics in the Validation of Physical Employment Standards

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Moull, Kimberley
physical employment standard , ergonomics , biomechanics
Physical Employment Standards (PES) are applied to test candidates’ abilities as required to perform a job safely and efficiently. Ability in this context refers to capacity (e.g., sufficient strength) and movement competency (e.g., technique). From the perspective of construct validity, physiological, psychophysical, and strength-based metrics are often applied as they reflect important constructs of capacity. However, objective metrics related to movement competency seem to be lacking in the context of PES. Two types of PES-based tests are commonly applied to assess candidates’ abilities: task predictive tests (TPT), where candidate’s actions are designed to predict job performance, and task simulation tests (TST), where candidate’s actions are directly simulated from the actual job. The current study explores if the use of movement-based metrics reveals meaningful information about the validity of a TPT relative to a TST. Participants were sixteen former manual materials handling employees. Participants performed a TPT and a TST, where each was designed based on the same underlying job description (box and container lifting tasks). Three-dimensional trunk and upper limb motion, and electromyography (EMG) of the back and shoulders were collected during each test. Joint angles and maximum voluntary isometric contractions were processed from raw motion and EMG data, respectively. Cross-correlation was applied to all data to assess the differences in the movement-based waveforms between the two types of tests. Kinematic and EMG outcomes were generally similar between the tests (R > 0.8) with two exceptions: Trunk flexion/extension angles were the least similar between TPT and TST during container tasks (R < 0.8) compared to other tasks, and EMG at the shoulders were the least similar during the heavier box tasks (R < 0.8) compared to other tasks. The TPT generally elicited similar movement-based patterns compared to the TST, demonstrating construct validity with respect to movement competency. However, the TST required participants to adopt different movement strategies, particularly when the use of actual containers changed the grip demands relative to the TPT. The TPT should consider handle characteristics if the test is being used to assess both capacity and competency with respect to actual job demands.
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