Sean R. Mitchell

Human perceptions of sports equipment under playing conditions

Assessment of the ‘performance’ of sports equipment is generally derived from physical and technical parameters, such as power, speed, distance and accuracy. However, from a psychological perspective, players need to feel comfortable with their equipment and confident in its properties. These factors can only be measured through the subjective assessment of individual perceptions. Focusing on a group of elite golfers, this study presents a formalized approach for eliciting and structuring players’ descriptions of their perception of sports equipment. Qualitative methods of inquiry were used to generate perceptions from a group of professional golfers ( n = 15) during play testing. The equipment characteristics of significance to the golfers emerged from an inductive analysis of their responses. However, although this method of representation of the results helped to identify the key components or dimensions of a players subjective perception, it was unable to determine potential relationships between the dimensions. With this in mind, a new technique, called structured relationship modelling’, was developed. Ten general dimensions emerged from the analysis, of which three are presented here together with a section of the relationship model. The results demonstrate the effectiveness of qualitative techniques for eliciting human perceptions and of structured relationship models for representation of the associations found.

The evaluation of new multi-material human soft tissue simulants for sports impact surrogates

Previous sports impact reconstructions have highlighted the inadequacies in current measures to evaluate the effectiveness of personal protective equipment (PPE) and emphasised the need for improved impact surrogates that provide a more biofidelic representation of human impact response. The skin, muscle and subcutaneous adipose tissues were considered to constitute the structures primarily governing the mechanical behaviour of the human body segment. A preceding study by Payne et al. (in press) investigated the formulation and characterisation of muscle tissue simulants. The present study investigates the development of bespoke blends of additive cure polydimethysiloxane (PDMS) silicones to represent both skin and adipose tissues using the same processes previously reported. These simulants were characterised mechanically through a range of strain rates and a range of hyperelastic and viscoelastic constitutive models were evaluated to describe their behaviour. To explore the worth of the silicone simulants, finite element (FE) models were developed using anthropometric parameters representative of the human thigh segment, derived from the Visible Human Project. The multi-material silicone construction was validated experimentally and compared with both organic tissue data from literature and commonly used single material simulants: Dow Corning Silastic 3480 series silicones and ballistics gelatin when subject to a representative sports specific knee impact. Superior biofidelic performance is reported for the PDMS silicone formulations and surrogate predictions.

Feature-based systems for the design and manufacture of sculptured products

Many products having free form of sculptured surfaces are designed by traditional methods by crafting prototypes. This requires skill. Analysis of these products often reveals that they have an established general form and are designed around a number of dominant features. A feature-based design system is proposed based on extended surfaces and blends that provides designers with considerable flexibility for feature replacement and manipulation. The implications of this approach on the rapid production of prototypes for both design appreciation and manufacturability is discussed. A range of golf clubs has been used as the example around which the methodology has been developed.

The effects of ball impact location and grip tightness on the arm, racquet and ball for one-handed tennis backhand groundstrokes

A torque-driven, 3D computer simulation model of an arm-racquet system was used to investigate the effects of ball impact location and grip tightness on the arm, racquet and ball during one-handed tennis backhand groundstrokes. The stringbed was represented by nine point masses connected to each other and the racquet frame with elastic springs and three torsional spring-dampers between the hand and the racquet were used to represent grip tightness. For each perturbation of nine impact locations and grip tightness, simulations were run for a 50 ms period starting with ball-racquet impact. Simulations showed that during off-centre impacts below the longitudinal axis of the racquet, the wrist was forced to flex up to 16° more with up to six times more wrist extension torque when compared to a centre impact simulation. Perturbing grip tightness had no substantial effect on centre impact simulations. However, for off-centre impacts (below the longitudinal axis of the racquet) a tight grip condition resulted in a substantial decrease in racquet rotation within the hand (less than 2°) and an increase of 6° in wrist flexion angle when compared to the equivalent simulation with a normal grip. In addition there was approximately 20% more wrist extension torque when compared with equivalent off-centre impact simulation with a normal grip. Consequently off-centre impacts below the longitudinal axis of the racquet may be a substantial contributing factor for tennis elbow injuries with a tight grip aggravating the effect due to high eccentric wrist extension torques and forced wrist flexion.

Hollow golf club head modal characteristics: Determination and impact applications

The design of modern hollow golf club heads is a labor-intensive process involving extensive performance festing both by robotic and real golfers. This paper describes how, by correlating club head mechanical behavior with functional performance, it will become possible to use validated computational models to predict this performance as well as related contributions to the ill-defined concept of “feel”. Successful use of experimental modal analysis to validate a hollow golf club head finite element model is reported. Modal tests employing noncontacting, laser-based transducers facilitated identification of the natural frequencies and corresponding modeshapes for the three main surfaces of the club head. The experimental data suggest predominantly different modal characteristics for each surface, and this compares favorably with equivalent data obtained from the finite element model. The modal data are also used to identify surfaces responsible for particular frequency components present in the club head impact sound spectrum. The potential for detailed impact performance prediction using the finite element model is further demonstrated by comparison of computed and experimental club head acceleration measurements recorded during simulated and actual club-ball impacts.

A Structured Approach to the Design of Shoe Lasts

Abstract The foundation for sculptured feature-based shoe last design, using extended form (EF) feature methods, is presented. The EF approach is particularly suited to sculptured surface products that exhibit parametric variation throughout a set or family, such as shoe lasts. Some underlying principles and issues relevent to shoe lasts and common to sculptured products that can be usefully modelled by the EF feature approach are also discussed. An initial feature anatomy for a common shoe style is proposed to support the need for localized shape control for current and future design requirements. The following conclusions are reached: it is possible to decompose a shoe last into a feature anatomy for EF feature-based design; there are issues common to sculptured products, including shoe lasts, that are specifically addressed and dealt with effectively within the EF method; an EF feature-based approach shows significant potential to benefit last design efficiency, enhance size grading, and improve manufa...

Development of novel synthetic muscle tissues for sports impact surrogates

Impact injuries are commonplace in sport and often lead to performance detriment and debilitation. Personal Protective Equipment (PPE) is prescribed as a mandatory requirement in most sports where these impacts are likely to occur, though the methods of governance and evaluation criteria often do not accurately represent sports specific injury scenarios. One of the key shortcomings of such safety test standards is the human surrogate to which the PPE is affixed; this typically embodies unrepresentative geometries, masses, stiffness and levels of constraint when compared to humans. A key aspect of any human surrogate element is the simulant material used. Most previous sports specific surrogates tend to use off-the-shelf silicone blends to represent all the soft tissue structures within the human limb segment or organ; this approach potentially neglects important human response phenomena caused by the different tissue structures. This study presents an investigation into the use of bespoke additive cure Polydimethysiloxane (PDMS) silicone blends to match the reported mechanical properties of human relaxed and contracted skeletal muscle tissues. The silicone simulants have been tested in uniaxial compression through a range of strain rates and fit with a range of constitutive hyperelastic models (Mooney Rivlin, Ogden and Neo Hookean) and a viscoelastic Prony series.

Subject-specific computer simulation model for determining elbow loading in one-handed tennis backhand groundstrokes

A subject-specific angle-driven computer model of a tennis player, combined with a forward dynamics, equipment-specific computer model of tennis ball–racket impacts, was developed to determine the effect of ball–racket impacts on loading at the elbow for one-handed backhand groundstrokes. Matching subject-specific computer simulations of a typical topspin/slice one-handed backhand groundstroke performed by an elite tennis player were done with root mean square differences between performance and matching simulations of < 0.5°over a 50 ms period starting from ball impact. Simulation results suggest that for similar ball–racket impact conditions, the difference in elbow loading for a topspin and slice one-handed backhand groundstroke is relatively small. In this study, the relatively small differences in elbow loading may be due to comparable angle–time histories at the wrist and elbow joints with the major kinematic differences occurring at the shoulder. Using a subject-specific angle-driven computer model combined with a forward dynamics, equipment-specific computer model of tennis ball–racket impacts allows peak internal loading, net impulse, and shock due to ball–racket impact to be calculated which would not otherwise be possible without impractical invasive techniques. This study provides a basis for further investigation of the factors that may increase elbow loading during tennis strokes.

An initial data model, using the object-oriented paradigm, for sculptured-feature-based design

This paper presents an initial object [1] model based on entity/relationship [2] structures for sculptured-feature-based design. The model provides the basis for a system that will allow designers to define their products in terms of interacting features they recognise, and categories that are meaningful to their organisation. Design solutions can also be explored and ultimately defined by means of parametric shape algorithms and values relevant to a particular product domain. Finally, the three-dimensional geometry can be evaluated throughout the design activity for visualisation, analysis, and ultimately manufacture.

Development of a synthetic human thigh impact surrogate for sports personal protective equipment testing

Synthetic impact surrogates are widely used in the sporting goods industry in the evaluation of personal protective equipment. Existing surrogates, exemplified by those used in safety standards, have many shortcomings, primarily relating to their mass, stiffness, geometries and levels of constraint which limit their biofidelity and subsequent usefulness in personal protective equipment evaluations. In sports, absence from competition is a primary severity measure for injuries; consequently, blunt trauma injuries, such as contusions and lacerations, become pertinent and serious concerns. It is important, therefore, that synthetic surrogates provide an adequate description of these soft tissues to effectively evaluate injury risk. A novel, multi-material human thigh surrogate has been presented with consideration to the tissue structures, geometries and simulant materials used. This study presents the detailed development stages undertaken to fabricate a multi-material synthetic soft tissue surrogate with skin, subcutaneous adipose and muscle tissue components. The resultant surrogate demonstrates the successful use of sequential moulding techniques to construct a full-scale anatomical human impact surrogate which can be used in personal protective equipment testing.