A biomechanical analysis of hip compression loading during lifting

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Abstract
The aims of the present study were (i) to calculate the magnitude and direction of the hip joint compressive force, (ii) to determine the influence of hip flexion angle on the compressive force and (iii) to design a diagram for easy predictions of hip extensor muscular forces. A biomechanical analysis was performed using data from dissection, combined with data from our previous investigations into hip load moments during lifting, and into length of hip extensor muscular moment arms. Waters' load-sharing data were also included in the biomechanical model. The compressive force during lifting a 126 N ( 12.8 kg) box in the sagittal plane with flexed and with straight knees was calculated to be between 2.6 and 3.2 times body weight and the force was found to be directed medially and slightly dorsally. At a constant hip joint loading moment, the degree of hip flexion greatly influenced the compressive force, the least force being obtained at 35° hip flexion. The use of the force prediction diagram developed is described. This diagram is proposed for practical use when assessing different work postures.