# Are Torque-Driven Simulation Models of Human Movement Limited by an Assumption of Monoarticularity?
## 3 Results
### Countermovement Jump  
The descent phase of the countermovement jump was matched with similar accuracy by both the SJ and TJ simulations, with no discernible differences in the techniques (9\({}^{\circ}\) differences between measured performance and matched simulations; Table 7, Figures 5 and 6). The results for the ascent phase of the countermovement jump highlighted similar characteristics for between-model differences as those of the squat jump, but with differences of typically larger magnitude. The overall difference between the SJ model and participant performance was 24.3%, and for the TJ model, 10.1% (Table 7). The TJ model closely matched the measured jump, with a peak mass centre height of 1.50 m, 6 cm smaller than the measured performance. The SJ model achieved a peak jump height of 1.38 m, 18 cm smaller than the measured performance, with most of this difference associated with the flight phase (14 cm), and therefore, the take-off velocity, rather than the mass centre height at take-off. The larger differences for the SJ model relate to a poorer capacity to match the measured joint kinematics at all joints. The optimised activation parameters of the full countermovement jump highlighted a requirement by both the SJ and TJ simulations for fewer than two ramps during the descent phase of the countermovement, and in the case of the ascent phase, often a single ramp was not required in the SJ simulation (Tables 5 and 6). In the case of the SJ simulation, during the ascent phase, either a uniform activation or a small ramp in activation was employed. The TJ simulation again demonstrated sequential timing of ramps for the biarticular and monoarticular plantar flexors and knee extensors. The TJ model was able to demonstrate different approaches to the application of the monoarticular and biarticular knee flexors, with a large activation of the biarticular component (also a hip extensor) and a small submaximal activation of the monoarticular component (less than 40% activation). The SJ simulation is incapable of having both large and submaximal activations of the knee flexors and so had a uniform large, but not maximal, knee flexor activation throughout much of the simulation. Hip flexor and hip extensor activation profiles were broadly similar for the SJ and TJ simulations, but despite the availability of multiple ramps, the SJ simulation employed far fewer than those available and adopted broadly single ramp profiles across the full descent and ascent phase. The duration of the simulation was markedly longer for the SJ model than the TJ model (SJ model 0.5 s, TJ model 0.4 s, measured 0.35 s), which enabled the SJ simulation to have a proportionally higher mass centre height at take-off. The ankle joint kinematics for both the SJ and TJ models had similar characteristics to those of the squat jump. At the knee and hip joints, there was a clear similarity between the kinematics adopted by the TJ model and the measured performance, but the SJ model adopted a very different technique at the knee and achieved much smaller velocities at the hip (Figures 5-7). In general, the errors in joint kinematics for the ascent phase differed by an additional 8-10\({}^{\circ}\) compared  
Figure 4: Squat jump; SJ (dashed black line), TJ (solid grey line), measured (solid black line); (a) orientation, (**b**) ankle, (**c**) knee, (**d**) hip angles. to the TJ model. As for the squat jump, the SJ countermovement jump achieved a smaller lower-limb joint extension than the TJ equivalent (Figure 7). At the ankle, the SJ model had 20\({}^{\circ}\) less extension at take-off than the measured performance, whilst this was 1\({}^{\circ}\) for the TJ model. At the knee, the SJ model had 30\({}^{\circ}\) less extension at take-off than the measured performance, whilst this was 6\({}^{\circ}\) for the TJ model. At the hip, the SJ model had 24\({}^{\circ}\) less extension at take-off than the measured performance, whilst this was 7\({}^{\circ}\) for the TJ model.