Interaction effects of stoop, full-squat, and semi-squat lifting techniques and hand-load position, magnitude, and asymmetry on knee and spine loads; a subject-specific musculoskeletal modeling investigation

Articles in Press

Document Type : Research Article

Authors

Department of Mechanical Engineering, Sharif University of Technology, Tehran, Iran

10.24200/sci.2026.66805.10257

Abstract

Main effects of three lifting techniques (LT: stoop, semi-squat, and full-squat) and their interaction effects with task-related parameters (hand-load positions/magnitudes) on spine/knee loads and directions were investigated. Previous studies have investigated the effects of stoop and full-squat LTs on spine/knee loads, ignoring their interaction effects with hand-load positions/magnitudes. Twenty-two individuals performed 36 load-handlings at twelve load positions adopting three LTs. Full-body posture was measured using a Vicon system. Musculoskeletal models in AnyBody software were derived to estimate L5-S1 and knee loads considering four hand-loads.  Hand-load magnitudes were simulated in the musculoskeletal model under identical kinematics; trials were recorded without hand-held loads to avoid fatigue. The adopted LT had a significant effect on the L5-S1 load magnitudes and knee load directions (p<0.05). All task-related parameters had significant interaction effects with the LT on both the spine and knee loads (p<0.05). Adopting a semi-squat technique generated the largest L5-S1 loads (5-20% higher than other LTs) and consequently the highest spine injury risk. The semi-squat LT generally generated similar/smaller knee loads magnitudes as compared to other LTs. Accurate knee injuries risk assessment between stoop and squat LTs, however, required finite element simulations due to the changes in knee load-bearing contact areas at different knee flexions. Semi-squat liftings should be avoided in real workplaces, especially for workers with spinal disorders. Semi-squat lifting was, however, a safer technique than full-squat for individuals with knee injuries. Depending on the hand-load position and magnitude, this study identified the safer lifting technique to prevent spine and/or knee injuries.

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Scientia Iranica

Articles in Press, Accepted Manuscript
Available Online from 24 July 2026

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History

  • Receive Date: 23 April 2025
  • Revise Date: 23 November 2025
  • Accept Date: 07 June 2026

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