Abstract
Subject-specific torque-driven computer simulation models employing single-joint torque generators have successfully simulated various sports movements with a key assumption that the maximal torque exerted at a joint is a function of the kinematics of that joint alone. This study investigates the effect on model accuracy of single-joint or two-joint torque generator representations within whole-body simulations of squat jumping and countermovement jumping. Two eight-segment forward dynamics subject-specific rigid body models with torque generators at five joints are constructed—the first model includes lower limb torques, calculated solely from single-joint torque generators, and the second model includes two-joint torque generators. Both models are used to produce matched simulations to a squat jump and a countermovement jump by varying activation timings to the torque generators in each model. The two-joint torque generator model of squat and countermovement jumps matched measured jump performances more closely (6% and 10% different, respectively) than the single-joint simulation model (10% and 24% different, respectively). Our results show that the two-joint model performed better for squat jumping and the upward phase of the countermovement jump by more closely matching faster joint velocities and achieving comparable amounts of lower limb joint extension. The submaximal descent phase of the countermovement jump was matched with similar accuracy by the two models (9% difference). In conclusion, a two-joint torque generator representation is likely to be more appropriate for simulating dynamic tasks requiring large joint torques and near-maximal joint velocities.
Highlights
An understanding of optimal sporting technique has been derived from subjectspecific torque-driven computer simulations of human movement
The aim of this study was to investigate whether the incorporation of TJ torque generators in addition to SJ torque generators in a computer simulation model improves accuracy when simulating maximal squat jumps and countermovement jumps
It was found that the use of subject-specific TJ representations of lower-limb joint torques rather than SJ representations resulted in smaller differences between the simulation model and measured performances for both squat and countermovement jumps
Summary
An understanding of optimal sporting technique has been derived from subjectspecific torque-driven computer simulations of human movement (e.g., tumbling takeoff [1], high jumping take-off [2], triple jumping [3], vaulting [4]). The torque-driven approach lumps synergistic muscle forces together and typically has fewer unknown parameters that must be sourced from the literature as compared to individual muscle-model simulations [5]. The two distinct modelling approaches have different fundamental strengths: the torque-driven approach enables a focus on the technique or movement coordination with accurate strength representation, whilst the muscle-driven model enables the investigation of individual muscle and tendon properties, but with reduced accuracy of the strength capabilities of the system [6]. An added benefit of the torque-driven approach is that the simulation model can represent a specific individual, and simulations may be evaluated against a measurable performance to assess model accuracy [7]. Torquedriven simulation models have achieved differences from performance measures of 10%
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