Computer Simulations of Planar Sports Motions

The computer simulation and the associated problem of the optimization of sports motions is a comparatively new field of biomechanical research. Until recently, the majority of investigations were concerned with the analysis of specific attributes of a certain discipline, usually neglecting all other facets of the investigated phenomenon. This view has now changed in favour of a more holistic one. However, very little experience has been gained up to now in the field of computer simulation of sports motions. One of the reasons for this lack is certainly to be found in the high degree of mathematical sophistication required to deal with the intricacies associated with the computer simulation of the human neuromusculoskeletal system. Only a team of mathematicians, numerical analysts and computer scientists is in a position to develop the necessary algorithms and computer programs. In this paper we shall present an overview of some of the major problems relating to the computer simulation of planar (2-D) motions and give an example of a long jump simulation. We shall deal mainly with the skeletal subsystem of the total neuromusculoskeletal system since a discussion of the complexities of the muscular and neural subsystem is beyond the scope of this presentation

BIOMECHANICS OF SPORTS - SELECTED EXAMPLES OF SUCCESSFUL APPLICATIONS AND FUTURE PERSPECTIVES

The performance criteria of physical activities, especially those of sport disciplines, can usually be defined in biomechanico-mathematical terms. This implies that sufficiently complex models of the human neuromusculoskeletal system can be used for the simulation and analysis of sports motions and, at least in principle, for the biomechanical optimization of the performance in the various sport disciplines. It is frequently forgotten that biomechanical optimization, in the widest sense, is the ultimate goal of the majority of all endeavors in sports biomechanics, even if this may not always be obvious. Examples of the successful generation of biomechanical models include adequate models of the human skeletal and muscular subsystem, and the creation of a functional racket-hand-arm system model for simulating tennis strokes. Simultaneously, anthropometrico-computational and dynamometric methods were developed for determining respectively the subject-specific segmental and myodynamic parameter sets. The models and methods just mentioned will be illustrated during the oral presentation. As regards the practical applications of the biomechanical modelling approach to sports, some selected examples also to be presented are: the complete optimization of a kicking motion; the successful computer simulation and analysis of a rock ' n roll Betterini somersault in connection with an accident requiring a biomechanical expert opinion; the development of an objective biomechanical method for testing the quality criteria of tennis rackets; the quantification of the variability of repeated sports motions; and investigations into the validity and reliability of vertical jumping performance testing methods. Needless to say that appropriate biomechanical models of the human neuromusculoskeletal system are indispensable in theoretical studies such as the demonstration of the comparatively high insensivity of skeletal motions to neural control perturbations. Considering the current state of the art it would appear that contemporary biomechanics of sports is still too pre-occupied with measurement, data collection, and the subsequent phenomenological description of an observed event instead of asking the (much more difficult) question concerning the causes and fundamental mechanisms underlying the observed phenomenon. The mere measurement and description of the ground reaction forces during the release phase of the javelin throw, for instance, without relating their significance to the musculoskeletal factors that determine the throwing distance, is meaningless and constitutes a futile exercise. As a future trend in sport biomechanics, the utilization of models for performance optimization may be expected to gain increasing importance

POWER ASSESSMENT OF INDIVIDUAL LEG MUSCLE GROUPS BY MULTISTRUCTURAL ANALYSIS OF SYMMETRIC VERTICAL MAXIMUM EFFORT JUMPS

A method is introduced which permits the quantification of individual muscle work contributions occurring in the joints of a segmented body model in all phases of bi-legged vertical jumping. In this way, the evolution in time of the performance criterion can be monitored and deficiencies in the muscle groups involved can be detected. It is also shown that point mass body models are inadequate for relating jumping performance and muscle power contributions

Biomechanics-based in silico medicine: The manifesto of a new science

In this perspective article we discuss the role of contemporary biomechanics in the light of recent applications such as the development of the so-called Virtual Physiological Human technologies for physiology-based in silico medicine. In order to build Virtual Physiological Human (VPH) models, computer models that capture and integrate the complex systemic dynamics of living organisms across radically different space–time scales, we need to re-formulate a vast body of existing biology and physiology knowledge so that it is formulated as a quantitative hypothesis, which can be expressed in mathematical terms. Once the predictive accuracy of these models is confirmed against controlled experiments and against clinical observations, we will have VPH model that can reliably predict certain quantitative changes in health status of a given patient, but also, more important, we will have a theory, in the true meaning this word has in the scientific method. In this scenario, biomechanics plays a very important role, biomechanics is one of the few areas of life sciences where we attempt to build full mechanistic explanations based on quantitative observations, in other words, we investigate living organisms like physical systems. This is in our opinion a Copernican revolution, around which the scope of biomechanics should be re-defined. Thus, we propose a new definition for our research domain “Biomechanics is the study of living organisms as mechanistic systems”

A Comparison of Two Landing Styles in a Two-foot Vertical Jump

In team sports, such as basketball and volleyball, the players use different takeoff styles to make the vertical jump. The two-foot vertical jump styles have been classified according to the landing style and identified as hop style, when both feet touch the ground at the same time, and step-close style, when there is a slight delay between the first and second foot making contact with the ground. The aim of this research is to identify the differences between the two styles. Twenty-three subjects participated in the study, of whom 14 were volleyball players and 9 were basketball players. The jumps were video recorded and synchronized with two force platforms at 250 Hz. Two temporal periods of the takeoff were defined according to the reduction or increase in the radial distance between the center of gravity (CG) and the foot support (T - RDCG and T + RDCG, respectively). The findings produced no specific advantages when both styles were compared with respect to takeoff velocity and, consequently, to jump height, but takeoff time was significantly shorter (p < 0.001) in the hop style takeoff. However, this reduction was compensated for by the greater time employed in the last step of the approach run (p < 0.001). When the step-close style was used, the vertical velocity of CG at the beginning of the takeoff is significantly lower. Moreover, the mean vertical force developed during T - RDCG was reduced by -627.7 ± 251.1 N, thus lessening impact on landing. Horizontal velocity at the end of the takeoff is less when the step-close style is used (p < 0.005), suggesting that this style is better for jumps where it is necessary to move horizontally during the flight against an opponent

Jet Spaces in Modern Hamiltonian Biomechanics

In this paper we propose the time-dependent Hamiltonian form of human biomechanics, as a sequel to our previous work in time-dependent Lagrangian biomechanics [1]. Starting with the Covariant Force Law, we first develop autonomous Hamiltonian biomechanics. Then we extend it using a powerful geometrical machinery consisting of fibre bundles and jet manifolds associated to the biomechanical configuration manifold. We derive time-dependent, dissipative, Hamiltonian equations and the fitness evolution equation for the general time-dependent human biomechanical system. Keywords: Human biomechanics, covariant force law, configuration manifold, jet manifolds, time-dependent Hamiltonian dynamicsComment: 16 pages, 3 figure

The effect of barbell load on vertical jump landing force-time characteristics

The aim of this study was to quantify the effect that barbell load has on the jump height and force-time characteristics of the countermovement jump (CMJ). Fifteen strength-trained men (mean ± SD: age 23 ± 2 years, mass 84.9 ± 8.1 kg, height 1.80 ± 0.05 m) performed three CMJ with no additional load, and with barbell loads of 25%, 50%, 75%, and 100% of body mass on two force plates recording at 1000 Hz. Propulsion and landing force-time characteristics were obtained from force-time data and compared using analysis of variance and effect sizes. Jump height decreased significantly as load increased (26 to 71%, d = 1.80 to 6.87). During propulsion, impulse increased with load up to 75% of body mass (6 to 9%, d = 0.71 to 1.08), mean net force decreased (10 to 43%, d = 0.50 to 2.45) and time increased (13 to 50%, d = 0.70 to 2.57). During landing, impulse increased as load increased up to 75% of body mass (5 to 12%, d = 0.54 to 1.01), mean net force decreased (13 to 38%, d = 0.41 to 1.24), and time increased (20 to 47%, d = 0.65 to 1.47). Adding barbell load to CMJ significantly decreases CMJ height. Furthermore, CMJ with additional barbell load increases landing phase impulse. However, while mean net force decreases as barbell load increases, landing time increases so that jumpers are exposed to mechanical load for longer. Practitioners should exercise caution when implementing loaded CMJ to assess their athletes

Control of position and movement is simplified by combined muscle spindle and Golgi tendon organ feedback

Whereas muscle spindles play a prominent role in current theories of human motor control, Golgi tendon organs (GTO) and their associated tendons are often neglected. This is surprising since there is ample evidence that both tendons and GTOs contribute importantly to neuromusculoskeletal dynamics. Using detailed musculoskeletal models, we provide evidence that simple feedback using muscle spindles alone results in very poor control of joint position and movement since muscle spindles cannot sense changes in tendon length that occur with changes in muscle force. We propose that a combination of spindle and GTO afferents can provide an estimate of muscle-tendon complex length, which can be effectively used for low-level feedback during both postural and movement tasks. The feasibility of the proposed scheme was tested using detailed musculoskeletal models of the human arm. Responses to transient and static perturbations were simulated using a 1-degree-of-freedom (DOF) model of the arm and showed that the combined feedback enabled the system to respond faster, reach steady state faster, and achieve smaller static position errors. Finally, we incorporated the proposed scheme in an optimally controlled 2-DOF model of the arm for fast point-to-point shoulder and elbow movements. Simulations showed that the proposed feedback could be easily incorporated in the optimal control framework without complicating the computation of the optimal control solution, yet greatly enhancing the system's response to perturbations. The theoretical analyses in this study might furthermore provide insight about the strong physiological couplings found between muscle spindle and GTO afferents in the human nervous system. © 2013 the American Physiological Society