Loic Damm

The evaluation of traditional and early driver training with simulated accident scenarios

Objective: We assessed the driving skills of novice traditionally trained, novice early-trained, and experienced drivers to evaluate whether supervised early training could improve young drivers’ skills. Background: The overall representation of young male drivers in car crashes is a recurrent problem in developed countries. To prevent this overrepresentation, France institutes an early driver training program from the age of 16 with the supervision of an adult. However, evidence of the positive effects of this system is still lacking. Method: Three groups of drivers (12 participants each) were confronted with five prototypical accident scenarios introduced in a simulated urban circuit. Drivers’ response time, speed, and vehicle position in the lane were analyzed. Results: No difference was detected across groups regarding obstacle detection, as revealed by the analysis of response times. But in some unexpected scenarios, position control by traditionally trained drivers was more conservative than for more experienced drivers, and early-trained drivers were far more likely to respond with efficient evasive action. Conclusion: The exposure gained by an early training program could thus increase the development of visuomotor coordination and involve better skills in challenging situations. Application: The supplementary driving experience gained with the supervision of an adult during early training could promote the skills necessary to deal with risky situations. Driving simulators could be used to confront young drivers with a broad range of hazardous scenarios not commonly encountered in natural driving.

The development of an apparatus to understand the traction developed at the shoe–surface interface in tennis

The traction developed at the shoe–surface interface can have a significant influence on a player’s injury risk and performance in tennis. The purpose of this study was to investigate shoe–surface traction on a dry acrylic hard court and two artificial clay court tennis surfaces in dry and wet conditions. A laboratory-based mechanical test rig was developed to measure the traction force developed at the shoe–surface interface. Linear regression analysis was used to examine the relationship between normal force and three measures of traction: initial stiffness, peak traction force and average dynamic traction force. The normal force did not significantly influence the initial stiffness for the shoe–surface system on the acrylic hard court but did on the artificial clay surfaces. The infill particle size and the addition of moisture influenced the traction developed on the artificial clay surfaces. Small, dry particles developed greater traction and with a sufficiently high applied normal force will provide traction comparable to that on an acrylic hard court. However, increased particle size and/or the presence of moisture generally reduced traction. Strong and significant positive linear relationships were found between peak traction force and average dynamic traction force for all surface types and conditions. This study improves the understanding of the influence surface characteristics have on shoe–surface traction mechanisms. Once traction mechanisms are understood, surface properties and/or footwear can be effectively changed to maximise performance and/or minimise injury risk.

The effects of surface traction characteristics on frictional demand and kinematics in tennis

The interaction between footwear and surfaces influences the forces experienced by tennis players. The purpose of this study was to investigate traction demand and kinematic adaptation during tennis-specific movements with changes in traction characteristics of surfaces. We hypothesised that players would increase the utilised coefficient of friction (horizontal to vertical ground reaction force ratio) when the shoe surface combination had a high coefficient of friction and flex their knee after contact to facilitate braking. Eight participants performed two separate movements, side jump out of stance and running forehand. Ground reaction force was measured and three-dimensional kinematic data were recorded. Clay surface and cushioned acrylic hard court (low vs. high shoe–surface friction) were used. The peak utilised coefficient of friction was greater on clay than the hard court. The knee was less flexed at impact on clay ( − 5.6 ± 10.2°) and at peak flexion ( − 13.1 ± 12.0°) during the running forehand. Our results indicate that tennis players adapt the level of utilised friction according to the characteristics of the surface, and this adaptation favours sliding on the low friction surface. Less knee flexion facilitates sliding on clay, whereas greater knee flexion contributes to braking on the hard court.

Understanding the influence of surface roughness on the tribological interactions at the shoe-surface interface in tennis

The traction provided by shoe–surface interactions in tennis can have an impact on player safety, performance and overall enjoyment of the sport. There is a requirement for an improved scientific understanding of the tribological interactions at the shoe–surface interface and the effects that footwear and surface characteristics have on the traction developed. The aim of this study was to investigate the influence surface roughness has on traction present during a sliding contact between a shoe and an acrylic hard court tennis surface. The substrate of acrylic hard court tennis surfaces are formed from a coating of a silica sand and acrylic paint mix, giving them variations in surface roughness characteristics. Mechanical traction tests were performed on five surfaces of varying roughness at normal forces of between 400 N and 800 N with a commercially available acrylic hard court tennis shoe (with a herringbone outsole pattern) and a shoe with a flat outsole. Significant linear relationships were found between dynamic traction force and normal force. A trend for decreased dynamic traction with increased roughness was found. When examined under a microscope after testing evidence of contact between the shoe and the surface decreasing with increased surface roughness was found. With the flat shoe, surface roughness affected the relationship between the coefficient of traction and the normal load. As roughness increased the coefficient of dynamic traction becomes less dependent on normal force. Evidence of a sudden increase in traction with the flat shoe when tested on the roughest surface suggests other friction mechanisms caused by the outsole overcoming the roughness of the surface, such as abrasive wear, had a significant effect on dynamic traction force.

Shoe-surface friction in tennis: influence on plantar pressure and implications for injury

Purpose. The different strategies employed by tennis players as a result of changes in friction properties of the playing surface are likely to influence injury incidence. Lower risk of injuries on surfaces that allow sliding has been reported. The aim of the present study was to characterise in-shoe pressure during tennis specific movements performed on a hard court and artificial clay in two surface-specific shoes.Methods. Two tennis surfaces were compared: artificial clay and cushioned acrylic hard court. Participants wore two different pairs of court-specific shoes on each surface. Seven (five males, two females) competitive tennis players performed three movements - open stance forehand, forehand plant (incorporated into a drill) and side jump. In-shoe plantar pressure distribution was recorded using the Pedar (Novel, Munich) insole system.Results. Significantly lower mean and peak pressure were measured during the side jump and running forehand plant on clay compared to hard court. Running forehand plant on artificial clay was characterised by a longer step duration and larger number of unloading episodes than on acrylic. Footwear did not influence peak pressures.Conclusions. A change in surface has a greater effect on plantar pressures than a change in shoe. The higher pressures on a hard court support an association for increased levels of overuse injuries. On clay, limiting areas of high pressure and a longer braking step could facilitate sliding by preventing sticking. Unloading episodes could also be part of the strategy aiming at sliding on clay. These differences are relevant to understand surface-specific mechanisms of injuries.

The influence of tennis court surfaces on player perceptions and biomechanical response

ABSTRACT This study aimed to examine player perceptions and biomechanical responses to tennis surfaces and to evaluate the influence of prior clay court experience. Two groups with different clay experiences (experience group, n = 5 and low-experience group, n = 5) performed a 180° turning movement. Three-dimensional ankle and knee movements (50 Hz), plantar pressure of the turning step (100 Hz) and perception data (visual analogue scale questionnaire) were collected for two tennis courts (acrylic and clay). Greater initial knee flexion (acrylic 20. 8 ± 11.2° and clay 32.5 ± 9.4°) and a more upright position were reported on the clay compared to the acrylic court (P < 0.05). This suggests adaptations to increase player stability on clay. Greater hallux pressures and lower midfoot pressures were observed on the clay court, allowing for sliding whilst providing grip at the forefoot. Players with prior clay court experience exhibited later peak knee flexion compared to those with low experience. All participants perceived the differences in surface properties between courts and thus responded appropriately to these differences. The level of previous clay court experience did not influence players’ perceptions of the surfaces; however, those with greater clay court experience may reduce injury risk as a result of reduced loading through later peak knee flexion.

Biomechanical and mechanical testing of non-sliding and sliding tennis surfaces

Tennis can be played on a variety of surfaces. The interaction between footwear and surfaces influences the forces experienced by players, suggesting a link between footwear/surface combinations an...

Combining mechanical and biomechanical testing to improve understanding of shoe-surface effects on traction

One feature of tennis is the possibility of playing on different types of surface which differ in their traction properties. Shoes with a specific outsole design for each type of surface are provided by manufacturers. The traction characteristics of the viscoelastic material of the outsole contacting a sport surface are dependent on the normal loading conditions. Currently tennis surface dynamic friction tests are conducted with a portable pendulum device. The pendulum test foot assembly applies an average normal force of 12 N (Lewis et al. 2011). The complex dynamics of human locomotion makes a full mechanical simulation of the human response to a surface an immense challenge. However, mechanical tests provide valuable insight into the traction characteristics of a shoe-surface combination. It is therefore important that both the normal loading conditions and the contacting interface between the player and the surface are relevant to play.