Jonathan R. Roberts

Evaluation of thin, flexible sensors for time-resolved grip force measurement

Abstract Three types of thin, flexible force sensor were studied under a variety of loading conditions to determine their suitability for measuring grip force. Static accuracy, hysteresis, repeatability, and drift errors were established, the effects of shear force and surface curvature were considered, and dynamic accuracy and drift were measured. Novel tests were developed to consider dynamic accuracy and sensitivity to shear loadings. Additionally, three sensors were evaluated in a real-life gripping scenario, measuring grip force during a golf shot. Comments are made on sensor performance, ease of use, and durability.

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.

Measurement and analysis of grip force during a golf shot

In this study, grip force was measured during a standard golf tee shot using two different measurement techniques. The first utilized a matrix-type thin-film sensor applied to a golf grip, from which total grip force could be readily determined. The second method involved 31 individual thin-film force sensors strategically placed on two golf gloves, allowing the force output of specific regions of the hands to be measured. Twenty golfers of varying ability participated in each test. The discovery of a unique grip force ‘signature’ for each golfer emerged from these data. That is, each golfer had a very repeatable total grip force trace, but these traces varied considerably between golfers. High-speed video was also recorded for many of the golfers tested so that key phases in the swing could be identified on the force traces.

Human perceptions of artificial surfaces for field hockey

Measuring the performance of a sports surface is typically derived from a series of field and laboratory tests that assess the playing properties under simulated game conditions. However, from a player’s perspective their own comfort and confidence in the surface and its playing characteristics are equally if not more important. To date no comparative study to measure playing preference tests has been made. The aim of this research was to develop a suitable method for eliciting player perceptions of field hockey pitches and determine the key themes that players consider when assessing field hockey pitches. To elicit meaningful unbiased human perceptions of a playing surface, an individual subjective analysis was carried out, using interviews and inductive analysis of the recorded player statements. A qualitative analysis of elite hockey players (n = 22) was performed to obtain their perceptions immediately after a competitive match. The significant surface characteristics that emerged as part of an inductive analysis of their responses were grouped together and formed five general themes or dimensions: player performance, playing environment, pitch properties, ball interaction and player interaction. Each dimension was formed from a hierarchy of sub-themes. During the analysis, relationships between the dimensions were identified and a structured relationship model was produced to highlight each relationship. Players’ responses suggested that they perceived differences between pitches and that the majority of players considered a ‘hard’ pitch with a ‘low’ ball bounce facilitating a ‘fast’ game speed was desirable. However, further research is required to understand the relative importance of each theme and to develop appropriate measurement strategies to quantify the relevant engineering properties of pitch materials.

Driver swingweighting : a worthwhile process?

Abstract The concept that golf clubs should have a uniform weight distribution means that manufacturers invest significant time and money tailoring the swingweight of their clubs. If golfers are unable to perceive significant changes in swingweight, however, and the effect of swingweight on club performance is small, the current manufacturing tolerances on swingweight can be widened, allowing time and cost savings in the assembly process. Testing was conducted using 30 skilled golfers each performing ten tee-shots with four differently weighted drivers. Clubhead mass was varied using screwed inserts of different known masses and the effects on impact location and clubhead speed were both measured. Changes to golf club weight distribution, measured using the swingweight concept, were found to have little effect on player performance and, in general, golfers were unable to perceive small changes in club swingweight. Manufacturing tolerances for component masses appear to offer sufficient control over golf club weight distribution, suggesting that mass balancing procedures may be relaxed during club assembly to provide production time and cost savings.

Time-Resolved Measurements of Grip Force During a Golf Shot

Twenty golfers of varying ability took ten shots each with a standard golf club fitted with thin-film force sensors at the grip. Force was monitored at 84 locations, with the moment of impact determined for each shot. Evaluation of the sensor outputs has shown that each player has a grip force signature, i.e. total grip force throughout each shot is very repeatable for a given player, but varies considerably between players.

Determining the effect of cricket leg guards on running performance

Abstract Modern-day cricket has experienced a shift towards limited over games, where the emphasis is on scoring runs at a rapid rate. Although the use of protective equipment in cricket is mandatory, players perceive that leg guards, in particular, can restrict their motion. The aim of this study was to determine the influence of cricket leg guards on running performance. Initial testing revealed that wearing pads significantly increased the total time taken to complete three runs by up to 0.5 s compared with running without pads (P < 0.05). In addition, we found that the degree of impedance was dependent on pad design and could not be solely attributed to additional weight. To assess possible causes of reduced running performance, a biomechanical analysis was performed, investigating running kinematics, stride parameters, and ground reaction forces. The results revealed that the widest pad had the greatest effect on running kinematics, increasing hip abduction and decreasing hip extension, resulting in a shortened stride length (by 0.10 m) and increased stride width (by 0.12 m) compared with running without pads. Wearing pads also significantly increased peak braking force (by up to 0.3 times body weight [BW]), braking impulse (by up to 0.012 BW · s−1), peak mediolateral force (by up to 0.17 BW), and mediolateral impulse (by up to 0.016 BW · s−1) compared with running without pads, which resulted in reduced force applied in the direction of locomotion. The consequence of this reduction in running performance is an increased risk of being run-out or a reduction in the number of runs that could be scored from a particular shot.

Identifying the Modes Excited in a Tennis Racket by a Forehand Drive

During an impact between a tennis racket and a tennis ball, mechanical oscillations are excited in the frame and stringbed. These vibrations continue after the ball has left the stringbed and have been shown to contribute greatly to the ‘feel’ of the racket. During this research, lightweight accelerometers were used to measure frame vibrations excited by a typical forehand groundstroke. The results indicated that a number of modes are excited mainly below 1,000 Hz, both parallel (in-plane) and normal (out-of-plane) to the plane of the stringbed. Although the natural frequencies and damping ratios could be calculated, it was not possible to identify the respective mode shapes. A full experimental modal analysis (EMA) of the tennis racket was conducted to reveal the 3-D modal behaviour. Comparison of the two sets of data revealed that the frequencies excited during a tennis impact are both frame and stringbed modes. The frame modes include in-plane and out-of-plane bending modes as well as torsional modes. The next stage in this research is to identify the mode shapes that are undesirable to the player. The results presented in this paper would then enable racket designers to engineer rackets with better ‘feel’ qualities.

Incorporating subjective end-user perceptions in the design process: a study of leg guard comfort in cricket

During the design of sports equipment, the main focus is usually on physical performance attributes, neglecting key subjective factors such as feel or comfort. The personal protective equipment worn in sport is a typical example of where injury prevention has taken precedence over user comfort, but it is anticipated that, with an improved approach to the design process, comfort can be enhanced without sacrificing protection. Using cricket leg guards as an example, this study aims to develop a systematic method for assessing user perceptions and incorporating them into the design process. Using this method, players’ perceptions of the factors that influence comfort were elicited through the use of co-discovery sessions, focus groups, and individual interviews and analysed through an inductive process to produce a comfort model. The relative importance of the different comfort dimensions were identified through the use of an online questionnaire utilizing the analytical hierarchy process method. Through the combination of these methods, six general dimensions were identified with a weighting regarding the amount to which each one determines a users perceived comfort. These results demonstrate how subjective analysis can be integrated into the design process, allowing for end users’ preferences to be considered and integrated.

Elite players’ perceptions of football playing surfaces: a mixed effects ordinal logistic regression model of players’ perceptions

ABSTRACT The aim of this study was to determine potential explanatory factors that may be associated with different attitudes amongst the global population of elite footballers to the use of different surfaces for football. A questionnaire was used to capture elite football players’ perceptions of playing surfaces and a mixed effects ordinal logistic regression model was used to explore potential explanatory factors of players’ perceptions. In total, responses from 1129 players from 44 different countries were analysed. The majority of players expressed a strong preference for the use of Natural Turf pitches over alternatives such as Artificial Turf. The regression model, with a players’ country as a random effect, indicated that players were less favourable towards either Natural Turf or Artificial Turf where there was perceived to be greater variability in surface qualities or the surface was perceived to have less desirable properties. Player’s surface experience was also linked to their overall attitudes, with a suggestion that the quality of the Natural Turf surface players experienced dictated players’ support for Artificial Turf.