Figure 4.

Selection of load cases for L4, for seven activities involving spine movements ((A) forward flexion from upright standing to maximum flexion, (B) forward flexion from upright sitting, (C) in a seated position, twisting and lifting a box from the floor, from the right side to a table in front, (D) in a standing position, twisting and lifting a box from the floor, from the left side to the right side, and (E) in a standing position, lifting a box from the floor in front to the chest). Total reaction force at L4–L5 joint derived from the musculoskeletal model and normalised to body weight (BW) are shown as black lines. Dots indicate the frames selected for the finite element analysis. Load cases obtained with activities (C,D) were mirrored through the sagittal plane to obtain loading on the other side. Red, green, and blue dashed lines show X, Y, and Z components of the reaction force expressed in the vertebra coordinate system.