Advances in the development of whole body computer simulation modelling of sports technique

© ACAPS, EDP Sciences, 2013. Computer simulation models have been used to address a range of research questions in sports biomechanics related to understanding the mechanics of sports movements, contributions to performance, optimisation of sports technique and control of sports movements. This paper will describe how theoretical models used in sports biomechanics have been developed at Loughborough University over the last 20 years, detailing their various components, subject-specific parameters, model evaluation, key findings and the strengths / limitations and how models could be further progressed in the future. With each model a four stage methodology has been used to answer specific research questions: development of the simulation model, determination of subject-specific parameters, evaluation of the model, and application of the model. These computer simulation models have provided insight into the mechanics behind sports movements that would not be possible through observing performance and have established the factors that limit optimal performance. In the future computer simulation models of sports movements will continue to develop in terms of sophistication to include elements such as joint compression and will provide further insight into the mechanics underlying sports movements

The mechanics of the contact phase in trampolining

During the takeoff for a trampoline skill the trampolinist should produce sufficient vertical velocity and angular momentum to permit the required skill to be completed in the aerial phase without excessive horizontal travel. The aim of this study was to investigate the optimum technique to produce forward somersault rotation. A seven-segment, subject-specific torque-driven computer simulation model of the takeoff in trampolining was developed in conjunction with a model of the reaction forces exerted on the trampolinist by the trampoline suspension system. The ankle, knee, hip, and shoulder joints were torque-driven, with the metatarsal-phalangeal and elbow joints angle-driven. Kinematic data of trampolining performances were obtained using a Vicon motion capture system. Segmental inertia parameters were calculated from anthropometric measurements. Viscoelastic parameters governing the trampoline were determined by matching an angle-driven model to the performance data. The torque-driven model was matched to the performance data by scaling joint torque parameters from the literature, and varying the activation parameters of the torque generators using a simulated annealing algorithm technique. The torque-driven model with the scaled isometric strength was evaluated by matching the performance data. The evaluation produced close agreement between the simulations and the performance, with an average difference of 4.4% across three forward rotating skills. The model was considered able to accurately represent the motion of a trampolinist in contact with a trampoline and was subsequently used to investigate optimal performance. Optimisations for maximum jump height for different somersaulting skills and maximum rotation potential produced increases in jump height of up to 14% and increases of rotation potential up to 15%. The optimised technique for rotation potential showed greater shoulder flexion during the recoil of the trampoline and for jump height showed greater plantar flexion and later and quicker knee extension before takeoff. Future applications of the model can include investigations into the sensitivity of the model to changes in initial conditions, and activation, strength, and trampoline parameters

All Spun Out - Limits of aerial techniques when performing somersaults

The somersault is a key skill in gymnastics and diving. Almost all the rotation required must be performed while the athlete is airborne; whilst airborne the athlete’s angular momentum is constant. The postures chosen, and any postural change that occurs while airborne, will determine the rotation achieved by the athlete. Equations are derived that describe the possible rotational states in terms of the somersault and twist rotation, thereby determining which rotational states are possible and useful for performing somersaults and twisting somersaults. Equations describing the results of idealised postural changes intended to initiate twist in a somersault are also derived. Inertial property data was both collated from the literature and estimated from measurements of current athletes. The data thus represented a range of ‘possible athletes’ which were applied to the derived equations of motion to predict which skills are achievable using different postures and actions. Recommendations were made as to the ‘best’ twist initiation actions and postures to use for different somersault skills. For twisting somersaults it was shown that previously published aerial techniques, and slight variations of these, are inadequate to allow the majority of athletes to achieve the highest numbers of twists per somersault observed in current international competition. It was concluded that contact twist or aerial techniques yet to be mathematically described must be used. Based on the predictions of skills achievable it was clear that some athletes have a natural advantage over others. Further, it was found that the postures or techniques which were the ‘best’ for one athlete were not necessarily the ‘best’ for all athletes. Differences in predicted skill achievement and which posture or technique was most suitable varied with the gender and squad (related to age and years of training) but these categories did not explain all of the variation

Functional analysis of stability and variability in multiple forward somersaulting dives from the 3m springboard

Springboard diving is an evolving sport, with the degree of difficulty increasing for competition success. Understanding the underlying coordination strategies associated with performing complex dives is important to optimise performance. The overall aim of this body of work was to implement modern technology to investigate within-participant variability of springboard divers. Following accuracy testing, IMUs were used to measure multiple forward somersault dives. Discrete angular kinematic analysis demonstrated that divers achieved consistent Total Flight angular displacements by using a feedback control strategy to link and adapt the timing and rate of angular deceleration during the Opening phase. fPCA was employed to more definitively examine structural differences and magnitude of repetitive technical movement characteristics of angular velocity time-series. fPCA demonstrated that lower skill was associated with a random structure of angular velocity performance, larger magnitudes of variability and a larger number of significant correlations between angular velocity and performance kinematics. This was associated with learning to link the multiple phases of dive flight. Divers performing at a higher level of proficiency were more stable in their repeated performances, exhibiting greater aerial awareness and utilising a prospective feedback strategy. This allowed the more experienced divers to functionally adapt and control their angular velocity throughout the entire movement sequence. Within-participant study designs are important to preserve and understand the underlying nature, technique and strategies of individuals. It is recommended that future research should move from between-participant study designs, which produce normative values of performance, to within-participant designs to more proficiently examine individual performance, optimise technique, reduce performance error and improve overall skill

Computer simulation of the takeoff in springboard diving

A computer simulation model of a springboard and a diver was developed to investigate diving takeoff techniques in the forward and the reverse groups. The springboard model incorporated vertical, horizontal and rotational movements based on experimental data. The diver was modelled as an eight-segment link system with torque generators acting at the metatarsal-phalangeal, ankle, knee, hip and shoulder joints. Wobbling masses were included within the trunk, thigh and shank segments to allow for soft tissue movement. The foot-springboard interface was represented by spring-dampers acting at the heel, ball and toes of the foot. The model was personalised to an elite diver so that simulation output could be compared with the diver's own performance. Kinematic data of diving performances from a one-metre springboard were obtained using high speed video and personalised inertia parameters were determined from anthropometric measurements. Joint torque was calculated using a torque / angle / angular velocity relationship based on the maximum voluntary torque measured using an isovelocity dynamometer. Visco-elastic parameters were determined using a subject-specific angledriven model which matched the simulation to the performance in an optimisation process. Four dives with minimum and maximum angular momentum in the two dive groups were chosen to obtain a common set of parameters for use in the torque-driven model. In the evaluation of the torque-driven model, there was good agreement between the simulation and performance for all four dives with a mean difference of 6.3%. The model was applied to optimise for maximum dive height for each of the four dives and to optimise for maximum rotational potential in each of the two dive groups. Optimisation results suggest that changing techniques can increase the dive height by up to 2.0 cm. It was also predicted that the diver could generate rotation almost sufficient to perform a forward three and one-half somersault tuck and a reverse two and one-half somersault tuck.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

The mechanics of the table contact phase of gymnastics vaulting

A computer simulation model of the table contact phase of gymnastics vaulting was developed to gain an understanding of the mechanics of this phase of the vault. The model incorporated a gymnast and a vaulting table, and used a novel two-state contact phase representation to simulate the interaction between these two bodies during the table contact phase. The gymnast was modelled in planar form using seven segments, with torque generators acting at the wrist, shoulder, hip and knee joints. The model also allowed for shoulder retraction and protraction, displacement of the glenohumeral joint centre and flexion/extension of the fingers. The table was modelled as a single rigid body that could rotate. The model was personalised to an elite gymnast so that simulation outputs could be compared with the gymnast's performance. Kinematic data of vaulting performances were obtained using a optoelectronic motion capture system. Maximal voluntary joint torques were also measured using an isovelocity dynamometer, and a torque - angle - angular velocity relationship was used to relate joint torques to joint angles and angular velocities. A set of model system parameters was determined using a gymnast-specific angle-driven model by matching four simulations to their respective performances concurrently. The resulting parameters were evaluated using two independent trials, and found to be applicable to handspring entry vaults. The torque-driven model was successfully evaluated, and shown to produce realistic movements, with mean overall differences between simulations and recorded performances of 2.5% and 8.6% for two different handspring entry vaults. The model was applied to further understanding of the mechanics of the table contact phase of gymnastics vaulting. Optimisation showed that there was limited potential (1.3%) for the gymnast to improve performance through technique changes during the table contact phase. However, with additional changes in configuration at table contact post-flight rotation could be increased by 9.8% and post-flight height could be increased by 0.14m. Angular momentum was found to always decrease during the table contact phase of the vault, although the reductions were less when maximising post-flight rotation

The mechanics of twisting somersaults

Twisting movements are categorised into three mechanical types, named as DIRECT, COUNTER-ROTATION and TILT TWIST. Twisting techniques are studied using mathematical models. A mathematical inertia model is constructed to enable the determination of segmental inertia parameters from anthropometric measurements. A film analysis program is developed so that the angles, which specify the orientation and configuration of the body, may be derived from digitised film data. A computer simulation model, comprising 11 segments and 17 degrees of freedom, is constructed to represent the human body in free fall. The combined use of the three computer programs results in maximum errors of 3% for somersault and 9% for twist in ten filmed movements. The mechanics of twisting techniques are explained using simple mathematical models. An analysis of rigid body motions shows that there are two distinct modes of motion, named as the ROD MODE and the DISC MODE. It is shown that it is possible to change from one mode to the other by varying the angle of pike and this permits the twist to be increased or stopped or even reversed. The capacities of twisting techniques are determined using simulations. For twists from a piked position, delaying the extension from the pike can increase the twist rate although this does depend upon the particular technique used and the initial direction of somersault. The contributions of twisting techniques used in the filmed movements are determined using simulations based upon modifications of the film data. It is found that counter-rotation techniques made small contributions and that aerial techniques, which increased the angle of tilt, were the major contributors, even in movements where the twist was apparent at take off. Using the simulation model it is shown that the build up of twist in the unstable double layout somersault may be controlled by means of small asymmetrical arm movements during flight

Developing agile motor skills on virtual and real humanoids

Demonstrating strength and agility on virtual and real humanoids has been an important goal in computer graphics and robotics. However, developing physics- based controllers for various agile motor skills requires a tremendous amount of prior knowledge and manual labor due to complex mechanisms of the motor skills. The focus of the dissertation is to develop a set of computational tools to expedite the design process of physics-based controllers that can execute a variety of agile motor skills on virtual and real humanoids. Instead of designing directly controllers real humanoids, this dissertation takes an approach that develops appropriate theories and models in virtual simulation and systematically transfers the solutions to hardware systems. The algorithms and frameworks in this dissertation span various topics from spe- cific physics-based controllers to general learning frameworks. We first present an online algorithm for controlling falling and landing motions of virtual characters. The proposed algorithm is effective and efficient enough to generate falling motions for a wide range of arbitrary initial conditions in real-time. Next, we present a robust falling strategy for real humanoids that can manage a wide range of perturbations by planning the optimal contact sequences. We then introduce an iterative learning framework to easily design various agile motions, which is inspired by human learn- ing techniques. The proposed framework is followed by novel algorithms to efficiently optimize control parameters for the target tasks, especially when they have many constraints or parameterized goals. Finally, we introduce an iterative approach for exporting simulation-optimized control policies to hardware of robots to reduce the number of hardware experiments, that accompany expensive costs and labors.Ph.D