# Are Torque-Driven Simulation Models of Human Movement Limited by an Assumption of Monoarticularity?
###### Abstract
Therefore, concurrent joint actions at the joints crossed by biaarticular muscles allow them to have lengthening and shortening velocities that may differ from synergistic monoarticular muscles. A second proposed advantage of biariticality is to enable a wider range of torque generating solutions at each joint [23; 24; 25; 26], which may further allow biaarticular muscles to modulate torques and offer fine control of human movement [27; 28]. Mathematical representation of the torques measured at the ankle, knee and hip joints using a function of the kinematics of two-joints has provided a more accurate representation of torques across a wider range of multi-joint kinematics [11; 29; 30]. Furthermore, it has been mathematically demonstrated that a two-joint approach that accounts for biaarticular effects results in different joint torques than a model using a single-joint approach, and these differences could be large in magnitude [11]. In summary, the monoarticularity assumption incorporated in torque-driven simulation models of human movement, may incur errors in the work generated or the movement solutions employed to achieve a dynamic task. It has been previously proposed [31] that if a simulation had initial conditions with large amounts of kinetic energy, the assumption of monoarticularity might result in only small errors, since the additional work contribution by torque generators would be relatively small. The triple-jumping model by the authors of [3] offers a good example of the distribution of initial energies at the initiation of a simulation model of a dynamic task. At touchdown, the matched simulation model had an initial net energy of 3240 J and this comprised about 2600 J of kinetic energy. Also, the tumbling model by the authors of [1] had an initial touchdown energy of 2014 J and a final take-off energy only 4% larger using small ranges of joint motion during take-off. Therefore, the authors of [31] suggest that single-joint (monoarticular) assumptions for some tasks may be unwarranted when a greater proportion of the final energy of the simulation must be derived during the simulation rather than from the initial conditions. This implies that larger ranges of joint motion must be employed. Squat and countermovement jumps are two examples of dynamic activities that start from a stationary position and are frequently modelled using an individual-muscle modelling approach. The final energy of the system is generated wholly between the start of the motion until the take-off, and the ranges of joint motion are large. As such, modelling and simulating vertical jumps using subject-specific torque-drivensimulation models will allow the suitability of single-joint assumptions for modelling multi-joint activities to be critiqued. The purpose of this study was to investigate whether monoarticular and biarticular based simulation models achieve similar accuracy when simulating maximal squat jumps and countermovement jumps and when simulating submaximal movements, such as those involved in the initial downward movement of a countermovement jump.