Combined musculoskeletal finite element modeling of femur stress during reactive balance training.

The purpose of this study was to determine the material stresses experienced in the femoral neck during the stepping phase of recovery from a forward loss of balance achieved both using release from a static forward lean and rapid treadmill accelerations in 8 older adults. A scalable musculoskeletal model with 23 degrees of freedom and 92 force actuators was used to calculate joint reaction forces. A finite element model of the femur used joint reaction forces calculated by the musculoskeletal model to calculate the material stresses during stepping. Balance recovery from a static forward lean angle had a greater joint contact force and greater maximum tensile stress than a recovery from treadmill induced perturbations both before and after a training session. Hip joint contact loads were found to be large in magnitude, however, all stresses experienced by the bone are less than critical yield stresses for trabecular bone. We suggest that stepping balance recovery is safe for older adults with no obvious loss of bone density or strength and that analyses such as finite element analysis are necessary to understand stresses in the material at the joint level.