Isometric Strength During Scaffold End Frame Disassembly

Overexertion injuries comprise the largest category of nonfatal injuries among construction workers. These injuries typically occur when the biomechanical stresses associated with tasks such as lifting, carrying, pushing, etc., exceed the worker’s strength capacity. Two studies were conducted to measure the whole-body isometric strength capability of 56 construction workers. The first study examined the effect of four typical postures (2 symmetric lifts and 2 asymmetric lifts) associated with scaffold end frame disassembly. The effect of posture on isometric strength capability was significant; the strength capability ranged from 366 N to 676 N. The second study evaluated the effect of hand separation distance (46 cm, 86.4 cm, and 116.8 cm) and vertical hand placement (knuckle, elbow, and acromial heights) on isometric force during symmetric lifting postures. The interaction effect of hand separation distance - vertical hand placement on isometric strength capability was significant. The strength capability ranged from 334 N to 644 N. The data collected from these two studies are unique from other human strength databases because the data set includes the human strength data while handling large-size materials. This information will be useful for human-modeling software developers to validate their models, and will be invaluable for safety practitioners in designing jobs which will protect workers from injury or fatigue.