Application of a Kinematics-Driven Approach in Human Spine Biomechanics During an Isometric Lift

Eective prevention and treatment management of spinal disorders can only be based on accurate
estimation of muscle forces and spinal loads during various activities such as lifting. The
infeasibility of experimental methods to measure muscle and spinal loads has prompted the use of
biomechanical modeling techniques. A major shortcoming in many previous and current models
is the consideration of equilibrium conditions only at a single cross section, rather than along
the entire length of the spine, when attempting to compute muscle forces and spinal loads. The
assumption of extensor global muscles with straight rather than curved paths and of the spinal
segments as joints with no translational degrees-of-freedom, are additional issues that need to be
critically evaluated when simulating lifting tasks. The kinematics-driven approach, which satises
equilibrium conditions in all spinal directions and levels and yields spinal postures compatible with
external loads, muscle forces and nonlinear passive properties, while also taking into account the
wrapping of trunk muscles, is employed. Results demonstrate that, regardless of the method
used (optimization or EMG-assisted), single-level free body diagram models yield estimations
that grossly violate equilibrium at other levels. The computed results are also markedly leveldependent.
The crucial eects of the proper consideration of global muscles with curved paths
and of spinal segments with translational degrees-of-freedom when attempting to estimate muscle
forces and spinal loads in isometric lifting tasks are also demonstrated.