Optimisation of performance in running jumps

Running jumps such as the high jump and the long jump involve complex movements of the human body. The factors affecting performance include approach conditions, strength of the athlete and the muscle activation timings at each joint. In order to investigate the mechanics of jumping performances and the effect of these factors, an eight-segment, subject specific, torque-driven computer simulation model of running jumps was developed, evaluated and used to optimise performances of jumps for height and distance. Wobbling masses within the shank, thigh and trunk segments, and the ground-foot interface were modelled as non-linear spring-damper systems. The values for the stiffness and damping constants were determined through optimisation. The inertia data were obtained from anthropometric measurements on the subject using the inertia model of Yeadon (1990b). Joint torques predicted by the simulation model were expressed as a function of angular velocity and angle using data collected from an isovelocity dynamometer. The simulation model was evaluated by comparing the actual performances with simulations using kinematic and kinetic data collected. Movement of the wobbling masses was found to be in the region of 40 mm in the shank and thigh and 90 mm in the trunk. This movement resulted in a lower, more realistic initial peak in the ground reaction force. Co-contraction was found to occur at the joints during impact in order to increase the initial level of eccentric activation and also the rise time to maximum eccentric activation. Differences of 2% and 1% in the height and distance achieved were obtained between actual performances and simulations. An optimisation procedure was used to maximise the height reached and distance travelled by the mass centre, in simulations of jumps for height and distance respectively, by varying the torque generator activation time histories at each joint. An increase of 12% in the height reached by the mass centre in the jump for height and 14% in the distance reached by the mass centre in the jump for distance were achieved

Determination of subject-specific model parameters for visco-elastic elements

The determination of subject-specific model parameter values is necessary in order for a computer simulation model of human motion to be evaluated quantitatively. This study used an optimisation procedure along with a kinematically-driven simulation model of the contact phase in running jumps to determine the elastic parameters of segmental wobbling masses and the foot-ground interface. Kinetic and kinematic data were obtained on a running jump for height and a running jump for distance performed by an elite male high jumper. Stiffness and damping coefficients of the visco-elastic elements in the model were varied until the difference between simulation and performance was minimised. Percentage differences of 6% and 9% between the simulated and recorded performances were obtained in the jumps for height and distance respectively. When the parameters obtained from the jump for height were used in a simulation of the jump for distance (and vice versa) there was poor agreement with the recorded jump. On the other hand a common set of visco-elastic parameters were obtained using the data from both recorded jumps resulting in a mean difference of only 8% (made up of 7% and 10%) between simulation and performance that was almost as good as the individual matches. Simulations were not overly sensitive to perturbations of the common set of visco-elastic parameters. It is concluded that subject-specific elastic parameters should be calculated from more than a single jump in order to provide a robust set of values that can be used in different simulations

Evaluation of a torque-driven model of jumping for height

This study used an optimisation procedure to evaluate an 8-segment torque-driven subject-specific computer simulation model of the takeoff phase in running jumps for height. Kinetic and kinematic data were obtained on a running jump performed by an elite male high jumper. Torque generator activation timings were varied to minimise the difference between simulation and performance in terms of kinematic and kinetic variables subject to constraints on the joint angles at takeoff to ensure that joints remained within their anatomical ranges of motion. A percentage difference of 6.6% between simulation and recorded performance was obtained. Maximising the height reached by the mass centre during the flight phase by varying torque generator activation timings resulted in a credible height increase of 90 mm compared with the matching simulation. These two results imply that the model is sufficiently complex and has appropriate strength parameters to give realistic simulations of running jumps for height

Considerations that affect optimised simulation in a running jump for height

This study used a computer simulation model to investigate various considerations that affect optimum peak height in a running jump. A planar eight-segment computer simulation model with extensor and flexor torque generators at five joints, was formulated and customised to an elite male high jumper. A simulation was matched to a recorded high jumping performance by varying the activation profiles of each of the torque generators giving a simulated peak height of 1.99 m compared to the recorded performance of 2.01 m. In order to maximise the peak height reached by the mass centre in the flight phase the activation profiles were varied, keeping the same initial conditions as in the matching simulation. Optimisations were carried out without any constraints, with constraints on the angular momentum at takeoff, with further constraints on joint angles, and with additional requirements of robustness to perturbations of activation timings. A peak height of 2.37 m was achieved in the optimisation without constraints. Introducing the three constraints in turn resulted in peak heights of 2.21 m, 2.14 m and 1.99 m. With all three types of constraint included the peak height was similar to that achieved in the recorded performance. It is concluded that such considerations have a substantial influence on optimum technique and must be included in studies using optimised simulations

The effects of initial conditions and takeoff technique on running jumps for height and distance

This study used a subject-specific model with eight segments driven by joint torques for forward dynamics simulation to investigate the effects of initial conditions and takeoff technique on the performance of running jumps for height and distance. The torque activation profiles were varied in order to obtain matching simulations for two jumping performances (one for height and one for distance) by an elite male high jumper, resulting in a simulated peak height of 1.98 m and a simulated horizontal distance of 4.38 m. The peak height reached / horizontal distance travelled by the mass centre for the same corresponding initial conditions were then maximized by varying the activation timings resulting in a peak height of 2.09 m and a horizontal distance of 4.67 m. In a further two optimizations the initial conditions were interchanged giving a peak height of 1.78 m and a horizontal distance of 4.03 m. The four optimized simulations show that even with similar approach speeds the initial conditions at touchdown have a substantial effect on the resulting performance. Whilst the takeoff phase is clearly important, unless the approach phase and the subsequent touchdown conditions are close to optimal then a jumper will be unable to compensate for touchdown condition shortcomings during the short takeoff phase to achieve a performance close to optimum

Modelling the maximum voluntary joint torque / angular velocity relationship in human movement

The force exerted by a muscle is a function of the activation level and the maximum (tetanic) muscle force. In “maximum” voluntary knee extensions muscle activation is lower for eccentric muscle velocities than for concentric velocities. The aim of this study was to model this “differential activation” in order to calculate the maximum voluntary knee extensor torque as a function of knee angular velocity. Torque data were collected on two subjects during maximal eccentric–concentric knee extensions using an isovelocity dynamometer with crank angular velocities ranging from 50 to 450°s−1. The theoretical tetanic torque/angular velocity relationship was modelled using a four parameter function comprising two rectangular hyperbolas while the activation/angular velocity relationship was modelled using a three parameter function that rose from submaximal activation for eccentric velocities to full activation for high concentric velocities. The product of these two functions gave a seven parameter function which was fitted to the joint torque/angular velocity data, giving unbiased root mean square differences of 1.9% and 3.3% of the maximum torques achieved. Differential activation accounts for the non-hyperbolic behaviour of the torque/angular velocity data for low concentric velocities. The maximum voluntary knee extensor torque that can be exerted may be modelled accurately as the product of functions defining the maximum torque and the maximum voluntary activation level. Failure to include differential activation considerations when modelling maximal movements will lead to errors in the estimation of joint torque in the eccentric phase and low velocity concentric phase

Coordination variability as a % of leg extension phase for the ankle-knee coupling.

<p>Coordination variability as a % of leg extension phase for the ankle-knee coupling.</p

Participants’ characteristics.

<p>Participants’ characteristics.</p

Coordination variability as a % of leg extension phase for the knee-hip coupling.

<p>Coordination variability as a % of leg extension phase for the knee-hip coupling.</p

Peak Power and velocity (at 40% resistance) during the leg extension phase.

<p>Peak Power and velocity (at 40% resistance) during the leg extension phase.</p