Incorporating joint compliance within a rigid body simulation model of drop jumping

Abstract

Impact forces of up to 13 times bodyweight have been observed in dynamic jumping activities such as the triple jump [1]. It has long been accepted that the human skeletal system is capable of damping such impact shock waves and avoiding direct transmission of impact forces to internal structures. The force attenuating mechanisms responsible, including foot arch and heel pad compliance; lower extremity joint compression; and spinal compliance, have previously been overlooked in forward-dynamics whole-body simulation models in aid of simplistic representations. Indeed, a general assumption of the existing models has been the simplistic modelling of frictionless pin joints and fixed segment lengths. Pin joint representations have therefore resulted in unrealistic dissipation of force and acceleration throughout the body following impact and hence difficulty in accurately reproducing experimentally measured ground reaction forces [1]. Previous studies have attempted to overcome this limitation by modelling excessive wobbling mass movement or compression at the foot-ground interface to compensate for the lack of compression and thus force dissipation within the joint structures [1, 2, 3]. Allen et al.[1] stated that whilst unrestricted ground compression was appropriate for simulating performance, accurate internal force replication would require compliance elsewhere within the rigid link system. The purpose of this study was therefore to investigate the effect of incorporating joint compliance on the ability of a computer simulation model to accurately predict ground reaction forces during dynamic jumping activities.