Stratum corneum and epidermal layers change in terms of thickness and roughness with gender, age and anatomical site. Knowledge of the mechanical and tribological properties of skin associated with these structural changes are needed to aid in the design of exoskeletons, prostheses, orthotics, body mounted sensors used for kinematics measurements and in optimum use of wearable on-body devices. In this case study, optical coherence tomography (OCT) and digital image correlation (DIC) were combined to determine skin surface strain and sub-surface deformation behaviour of the volar forearm due to natural tissue stretching. The thickness of the epidermis together with geometry changes of the dermal-epidermal junction boundary were calculated during change in the arm angle, from flexion (90°) to full extension (180°). This posture change caused an increase in skin surface Lagrange strain, typically by 25% which induced considerable morphological changes in the upper skin layers evidenced by reduction of epidermal layer thickness (20%), flattening of the dermal-epidermal junction undulation (45-50% reduction of flatness being expressed as Ra and Rz roughness profile height change) and reduction of skin surface roughness Ra and Rz (40-50%). The newly developed method, DIC combined with OCT imaging, is a powerful, fast and non-invasive methodology to study structural skin changes in real time and the tissue response provoked by mechanical loading or stretching.

The purpose of this study is to assess the fundamental characteristics that cause a football to spin in a curve ball kick due to impact conditions, and then to examine how the change in spin affects the flight of the ball. Two experimental trials were carried out to examine the aerodynamic properties of footballs during flight. In the first trial, a football was projected with no spin at varying launch velocities and the trajectory of each flight measured and analysed. A drag coefficient was calculated for each test, based on a trajectory model. The second trial involved a football being fired with the same launch velocity, but varying spin conditions (spin axis horizontal in all cases). Again, the trajectory of each flight was measured and drag and lift coefficients were calculated. This information was used to simulate three typical game situations and the effects of foot impact offset distance and weather conditions were examined.

The purpose of this study is to assess the fundamental characteristics which cause a football to spin in a curve ball kick. The ball impact process was analysed initially with a high speed video camera running at 4500 frames per second to obtain the basic data for a computer simulation model. This simulation model showed suitable agreement although it slightly deteriorated during the latter half of impact. It was noted that rotation of the ball occurs, even if the kinetic coefficient of friction is nearly equal to 0 because of local deformation of the ball during impact around the foot allowing forces to be transmitted to the ball around its axis. The spin of the ball was found to increase with the offset distance between the foot and the axis of the ball and as the kinetic coefficient of friction was increased. The offset distance between the foot and the axis of the ball affects the spin more than the coefficient of friction. Varying the coefficient of friction from 0.0 to 1.0 produces an increase in spin of 13 rad s−1 at most. It was suggested that the most suitable offset distance, which makes the largest ball rotation was around 100 mm. A trade‐off was found between the ball speed and spin, for different offset distances.

The traction forces produced between an athlete’s footwear and the playing surface are a crucial factor influencing a player’s performance. Four primary factors affecting traction have been identified from literature: the sports specific movement, the footwear, the playing surface, and the environment. Many authors have investigated traction behaviour mechanically, using a variety of shoe and surface types, concluding that the traction generated at the shoe–surface interface is dependent on each shoe–surface combination (see work by Gheluwe et al., Cawley et al., and Villwocket et al., details given in main text). There has been little attempt in the literature, however, to try and explain the behaviour of the surface from the traction resistance measurements that were observed, perhaps owing to the complex number of variables involved. Furthermore, the variety of methodologies used in past research makes it difficult directly to compare datasets. This paper presents datasets comparing the traction behaviour of several carefully prepared surface systems and states, using three mechanical test procedures, and investigates the factors influencing traction resistance. Results highlight that properties of synthetic turf carpets (fibres and tuft spacing) and the density state of the crumbed rubber infill component and the stud size and configuration influence the maximum traction forces generated at the shoe–surface interface. The magnitude of stud penetration under controlled vertical loading is also presented. The findings of this study further demonstrate the importance of understanding the detail of the surface system under test, and that the infill state has a measurable effect. The design and operation of mechanical traction measurement equipment also demonstrates influences on the traction values measured, and the largest influence is the normal load applied. The FIFA standard test is shown to be less sensitive to infill state than other tests. Recommendations are made for more robust testing methods for future research.

Handling errors are often seen in professional rugby games and even more so in amateur rugby. This paper analyses the problem of ball mishandling using highspeed video footage of passes and a bespoke finger friction rig. The high-speed video analysis showed that when the ball is caught, often there is a fluctuating movement of the fingers over the surface of the ball. It also showed that the fingers move over the surface of the ball when the ball is thrown, confirming that the dynamic friction is a good measure of how easily a ball can be handled. Rugby ball surface samples were used, on a finger friction rig, to assess the coefficient of friction between the finger and the balls. The currently manufactured balls displaying the highest coefficients of friction in clean, dry conditions were the design with square, 'sharp' pimples and also the design with a mixture of small and large pimples. The most consistent ball across wet and dry conditions was the ball with round, large, densely populated pimples. It was also shown that when water is added to the surface of the ball or finger, there was little variation in performance between the ball varieties.