Elite tennis players are required to perform on a variety of tennis court surfaces which differ in mechanical characteristics, such as friction and hardness, influencing their performance and risk of injury. To understand the influence of surfaces on performance and injury risk, three studies were conducted to investigate tennis players' perceptions and biomechanical responses during tennis-specific movements on different court surfaces. In study 1, tennis players perceptions of acrylic and clay courts were identified following a thematic inductive analysis of semi-structured interviews (n = 7) to develop a series of visual analogue scales (VAS) to quantify perceptions during studies 2 and 3. Perceptions of predictability of the surface and players' ability to slide and change direction emerged, in addition to anticipated perceptions of grip and hardness. Study 2 aimed to examine the influence of court surfaces and prior clay court experience on perceptions and biomechanical characteristics of tennis-specific skills. Perception, kinematic, insole pressure and mechanical data were collected on an acrylic and a clay court. In agreement with findings reported in study 1, lower mechanical friction and hardness on the clay court were perceived and accompanied by less predictability and greater difficulty to change direction whilst being easier to slide. As result of sliding, players' adopted an altered technique on the clay court compared to the acrylic leading to reductions in loading provide evidence to explain lower injury risks previously reported on clay courts. Prior clay court experience did not influence players' perceptions. However, biomechanical response to the clay surface differed, such that players with high clay court experiences contacted the ground with an everted foot, believed to contribute to controlling sliding. Differences in perception-response relationships were reported between experience groups suggesting players with greater clay court experience are better able to choose an appropriate response to improve their performance. Friction properties of the surface may change during play on clay courts due to player movements and sliding on the court. Therefore there may be areas of expected and unexpected changes to friction to which players must respond to. Study 3 aimed to examine the influence of changes in friction and players awareness of these changes on perceptions and biomechanical response. Compared with study 1 and 2, players found it more difficult to identify differences in perceived grip during study 3, possibly due the smaller mechanical friction differences reported. Unexpected reductions in friction produced greater initial ankle inversion angles compared to the expected decreases in friction, increasing players' risk of injury. Lower horizontal and vertical loading rates were reported on the lower friction conditions where further sliding was reported; suggesting a reduced injury risk by allowing longer time spent applying the forces. This thesis has identified key perception variables that enabled a holistic understanding of perceptions and their interaction with biomechanical response. Mechanical friction was an important factor influencing players' ability to slide. Sliding on clay resulted in altered loading characteristics, pressure distributions and kinematics potentially reducing players' injury risk. Tennis players' experience of clay courts does not influence their perceptions of the surface but the response that players adopt, which lower their risk of injury and increase performance. It is important when playing on a clay court that friction properties are maintained across the court during a tennis match as much as possible to reduce injury risks, due to the influence of unexpected changes to friction on perceptions and response.

Sports scientists and trainers generally agree that the multidimensional training in tennis should start during early childhood in order to ultimately reach a professional playing standard. Evidence suggests that motor skills, including power, strength, agility, speed and explosive power, as well as mental strength and a highly developed neuromuscular coordinating ability are strongly correlated with the level of tournament performance. Turner&Dent (1996) found that 27% of all tennis injuries in junior players occur in the shoulder region. The shoulder girdle is prone to injury because of its ability to maximally accelerate and decelerate the arm while the arm maintains it maintains precise control over the racquet at ball contact. The purpose of this study was to determine whether the occurrence of shoulder injuries could be minimized in tennis players by following a specific exercise programme, focusing on the shoulder girdle. A total of 42 tennis players participated in this study. They were all aged between 14 and 18 years. Both males and females were used for the purpose of this study. All the players were training at the SA Tennis Performance Centre and the International Tennis Federation at the University of Pretoria. They were all elite tennis players practising daily and scheduled for standard major tournaments throughout the year. Each subject completed a questionnaire of his or her tennis and medical history. The players were then divided into a control group and an experimental group. Both groups completed a series of physical scientific tests, consisting of posture analysis, body composition, flexibility, functional strength of the upper body; and isokinetic power and endurance of the shoulder muscles. These tests were executed every 3 months over a 9-month period and the results of each battery of tests were used to adjust and upgrade the new programmes. The experimental group did specific preventative shoulder exercises 5 times a week in addition to their usual gymnasium programme twice a week, while the control group followed a normal strengthening programme twice a week. A medical doctor immediately evaluated any muscle stresses or pains throughout the year. At the end of the year the data was compared to determine the difference in injury occurrence between the two groups. There was a significant difference (p<0.05) in the distribution of the lean body mass with the Lean body mass at T1 being lower than the Lean body mass at T3 in the control group. In the experimental group the fat percentage showed a significant decrease (p<0.05) from T1 to T3. The distribution of the muscle percentage at T1 was significantly different (p<0.05) from the distribution of the muscle percentage at T3 in the experimental group with the muscle percentage at T1 being lower than the muscle percentage at T3. There was a significant difference between the control and experimental group for 1RM bench press (p<0.05) with the 1RM bench press measurements at T3 being lower for the control group than for the experimental group. Also, the 1RM bench press at T1 was lower than the 1RM bench press at T3 in the experimental group. The experimental group showed a significant increase from T1 to T3, peaking at T3 with the 1RM bench press. Results of the tests done to determine isokinetic muscle strength showed that a statistical significant correlation (p<0.05) was found with regard to the strength of the internal rotators of the non-dominant shoulder at T3, with the experimental group having a higher measurement than the control group. The internal rotators and external rotators of both the dominant and non-dominant shoulders were lower at T1 than at T3 in the experimental group (p<0.05). The external rotators of the non-dominant shoulder at T1 were lower than the external rotators of the non-dominant shoulder at T3 in the control group. Results of the tests done to determine flexibility showed a statistically significant difference with the internal rotators and external rotators of the dominant as well as the non-dominant shoulders being lower at T1 than at T3 in the experimental group. Also, the external rotators of the non-dominant shoulder of the control group were lower at T1 than at T3. Results of the tests done to determine posture showed that in the control group, 54.5% of the players had scoliosis at T1 as opposed to 40.9% at T3. In the experimental group 55% had scoliosis at T1 compared to the 30% at T3. In the experimental group, 55% of the players’ shoulder heights were not level at T1, compared to 30% at T3. 63.6% of the control group’s non-dominant shoulders were higher than the dominant shoulder at T1, compared to the 40.9% of subjects at T3. Among the subjects in the experimental group, 50% had a higher non-dominant shoulder and 5% a higher dominant shoulder at T1, compared to 25% and 5% respectively in the control group, at T3. Results of the tests done to determine the occurrence of injuries, showed that the subjects with no injuries in the control group stayed stable from T1 (54.5%) to T2 (54.5%) whereafter it increased to 59.1% at T3. The experimental group stayed stable from T1 (55.0%) to T2 (55.0%) where after it increased to 85% at T3. In the control group the percentage grade 1 and 2 injuries was 13.6% at T1, increasing to 18.2% at T2, and decreasing to 13.6% at T3. In the experimental group 15% of the subjects had grade 1 injuries at T1. This percentage increased to 30% at T2 where after it decreased to 15% at T3 again. The percentage of subjects with grade 2 injuries in the experimental group remained stable at 10.0% from T1 to T2. None of the subjects had grade 2 injuries at T3. In the control group 9% had grade 3 injuries at T1, with none at T2 and T3. In the experimental group the percentage of subjects with grade 3 injuries remained stable at 5.0% from T1 to T2. None of the subjects had grade 3 injuries at T3. In the control group 4.5% of subjects had grade 4 injuries at T1. This stayed more or less stable at T2 (4.6%) and increased to 9.1% at T3. In the experimental group 10.0% had grade 4 injuries at T1. None of the subjects had grade 4 injuries at either T2 or T3. In the control group 4.5% had grade 5 injuries at T1, none had it at T2, and 4.5% had it at T3. In the experimental group none of the subjects had grade 5 injuries at T1, T2 or T3. In the control group none of the subjects had grade 6 injuries at T1 or T3. At T2, however, 4.6% had grade 6 injuries. In the experimental group 5.0% of the subjects had grade 6 injuries at T1 and none had this type of injury at T2 or T3. In conclusion, the results indicate that a specifically designed exercise programme can help to diminish the risk of shoulder injuries in tennis players. It can also improve bi-lateral muscle strength in opposing muscle groups which are used in tennis. / Thesis (DPhil)--University of Pretoria, 2007. / Biokinetics, Sport and Leisure Sciences / unrestricted