Models incorporating pin joints are suitable for simulating performance but unsuitable for simulating internal loading

Abstract

Additional Information:• This article was published in the Journal of Biomechan- AbstractSimulation models of human movement comprising pin-linked segments have a potential weakness for reproducing accurate ground reaction forces during high impact activities. While the human body contains many compliant structures such a model only has compliance in wobbling masses and in the foot-ground interface. In order to determine whether accurate GRFs can be produced by allowing additional compliance in the footground interface, a subject-specific angle-driven computer simulation model of triple jumping with 13 pin-linked segments was developed, with wobbling masses included within the shank, thigh, and trunk segments. The foot-ground interface was represented by spring-dampers at three points on each foot: the toe, ball, and heel. The parameters of the spring-dampers were varied by a genetic algorithm in order to minimise the differences between simulated GRFs, and those measured from the three phases of a triple jump in three conditions: (a) foot spring compression limited to 20 mm; (b) this compression limited to 40 mm; (c) no restrictions. Differences of 47.9%, 15.7%, and 12.4% between simulation and recorded forces were obtained for the 20 mm, 40 mm, and unrestricted conditions respectively. In the unrestricted condition maximum compressions of between 43 mm and 56 mm were obtained in the three phases and the mass centre position was within 4 mm of the actual position at these times. It is concluded that the unrestricted model is appropriate for simulating performance whereas the accurate calculation of internal forces would require a model that incorporates compliance elsewhere in the link system.

Trade-offs between horizontal and vertical velocities during triple jumping and the effect on phase distances

“…A 13-segment planar torque-driven computer simulation model ( Figure 1) was developed to investigate triple jumping technique (Allen et al, 2010;Allen et al, 2012). The 13 segments comprised: head + trunk, two upper arms, two forearms and hands, two thighs, two shanks, two 2-segment feet, with wobbling masses within the shanks, thighs, and torso.…”

“…Each foot had three points of contact with the ground at the heel, ball (metatarsophalangeal joint), and toe. The foot-ground interface was modelled using horizontal and vertical non-linear springdampers situated at the heel, ball, and toe of each foot (Allen et al, 2012). Thirteen-segment simulation model with wobbling masses within the shank, thigh, and trunk segments, torque drivers at the ball, ankle, knee, hip, and shoulder joints (grey circles), angle drivers at the elbow joints (white circles), and spring-dampers at three points on each foot.…”

“…Wobbling mass parameters were taken from Allen et al (2012). Ground reaction forces were found to be relatively insensitive to wobbling mass parameters, so only the viscoelastic parameters representing the springs at the foot were included in the optimisation.…”

“…In order to do this a genetic algorithm (GA) (Carroll, 1996) minimised an objective function by varying 264 parameters: 12 stiffness and damping coefficients at the foot; 21 initial kinematic conditions comprising the orientation angle and angular velocity, configuration angles at the ankle, knee, and hip, and the horizontal and vertical COM velocities in each of the three phases; and 231 parameters comprising 77 torque generator parameters in each of the three phases. The objective function was composed of the percentage RMS differences between simulation and performance in: takeoff velocity, time of contact, time to peak force, magnitude of peak force, and overall RMS differences between the orientation, configuration, and force time histories (Allen et al, 2012).…”

The effect of increasing strength and approach velocity on triple jump performance

“…A 13-segment planar torque-driven computer simulation model was used to investigate triple jumping technique (Allen et al, 2010;Allen et al, 2012). The equations of motion for the system were developed using Autolev TM which generated code in Fortran using Kane's method.…”