The current thesis is written as a collection of four experimental studies, which aimed to examine possible antecedents of athlete burnout, as well as potential performance consequences of the social environment (i.e. coach-athlete relationship) and athlete burnout. The thesis adopts the integrated model of athlete burnout (Gustafsson et al,. 2011) as a theoretical framework to explore the athlete burnout construct. Chapter 1 provides an introduction to the thesis whilst Chapter 2 reviews specific research literature to establish the research area interest for the four experimental studies. Chapter 3: Validating a Measurement of Perceived Teammate Burnout The aim of the first experimental study was to validate a sport specific method of measuring perceptions of teammate burnout. The athlete burnout questionnaire (ABQ) was adapted to create the team burnout questionnaire (TBQ) with items relating to the three dimensions of burnout (i.e. exhaustion, reduced accomplishment, and sport devaluation) modified through referent-shift to represent the perceptions of teammates (i.e. team exhaustion, team reduced accomplishment, and team sport devaluation). A sample of 290 team sports athletes completed the athlete burnout questionnaire (ABQ) and the TBQ at a single time point. To validate the proposed TBQ as a measure of athletes' perceptions of teammates' burnout two statistical steps were carried out. In the first step, the ABQ and the TBQ were analysed using confirmatory factor analysis (CFA). The next step was to combine both models into one multi-trait/multi-method (MTMM) analysis to test for discriminant validity and convergent validity. Comparing the CFA and MTMM models identifies that the discriminate validity of the TBQ was statistically supported. The TBQ could be utilised by researchers to examine an athlete's perception of their social environment as previously the integrated model of athlete burnout (Gustafsson et al., 2011) indicated that stressful social relationship may be a possible antecedent of athlete burnout. Chapter 4: Examining Perceptions of Teammates' Burnout and Training Hours in Athlete Burnout Following on from the validation of the TBQ in Chapter 3, Chapter 4 aimed to explore whether athlete perceptions of their teammates burnout influence their experience of burnout symptoms. The second aim of the study was to investigate the influence of training hours on the development of athlete burnout. 140 team sport athletes on two occasions separated by 3 months completed a series of questionnaires including the ABQ, the TBQ, and a number of demographic questions (e.g., On average, how many hours do you train per week?). Global burnout scores (i.e. mean of the 15 items of the ABQ) for athlete burnout and actual team burnout level were used to carry out the statistical analysis for the main analysis. The actual team burnout level was calculated by taking the mean of athletes' burnout scores within each team. To assess whether athlete burnout and athletes' perceptions of team burnout changed across time points, paired samples t-tests were conducted. To determine whether training hours impact upon athlete burnout and athletes' perception of team burnout, hierarchical regressions and linear regressions were conducted. The dynamic nature of athlete burnout was highlighted following data collection as the athlete's score on global burnout significantly increased across the 3 month period. At the initial time point, the training hours were not significantly associated to athlete burnout or the perception of their teammate's burnout. However, the cumulative training demands over the course of the 3 months appeared to impact upon athlete burnout. The study also identified that an athlete's perception of their teammates burnout may be a possible athlete burnout antecedent as results indicated that athlete's perceptions of their social environment predicted athlete burnout. Chapter 5: The Role of Coach-Athlete Relationship Quality in Team Sport Athletes' Psychophysiological Exhaustion: Implications for Physical and Cognitive Performance Further to stressful social relationships, the integrated model of athlete burnout (Gustafsson et al., 2011) identified the coach-athlete relationship is related to the development of athlete burnout. Chapter 5 aimed to examine whether the quality of the coach-athlete relationship (i.e. closeness, commitment and complementarity) was related to the development of athlete exhaustion and the performance of athletes. Chapter 5 adopted a two phase design. Phase One, 82 athletes participants completed a quasi-experimental trial measuring physical performance during a 5-m multiple shuttle-run test, followed by a Stroop test to assess cognitive performance, provided three samples of saliva to measure cortisol, and a series of questionnaire (i.e., ABQ, coach-athlete relationship questionnaire (CART-Q), demographic and background questionnaire). Structural equation modelling revealed a positive relationship between the quality of the coach-athlete relationship and Stroop performance. Negative relationships existed between the quality of the coach-athlete relationship and cortisol responses to high-intensity exercise, cognitive testing, and exhaustion and athlete exhaustion. In Phase Two, twenty-five athletes completed the experimental procedure on a further two occasions each time separated by 3 months. Structural equation modelling analysis revealed that the coach-athlete relationship at the beginning of the season predicted athlete exhaustion in the middle of the season. The analysis also revealed that the coach-athlete relationship and athlete exhaustion were unrelated to the physical and cognitive performance of athletes at the end of the season. The results indicated that athletes who perceived their relationship with their coach as being close, committed and complementary were less likely to perceive themselves as exhausted. Additionally, indicating that low quality coach athlete relationship increase the likelihood of athletes experiencing symptoms of emotional and physical exhaustion. Chapter 6: The Physical Implications of Athlete Exhaustion and the Quality of Coach-Athlete Relationship: A Case Study Chapter 6 aimed to investigate whether athlete burnout and the quality of the coach-athlete relationship accounted for differences in sporting performance. Fourteen male footballers complete a series of questionnaires including the CART-Q and the ABQ on two occasions separated by 10 weeks. Across the 10 weeks the total distance athletes covered during games and training was monitored using global positioning systems (GPS) technology. Further to monitoring running performance athletes counter movement jump (CMJs) were recorded each week. A series of three mixed factor models were utilised to investigate the potential influence of athlete burnout and the quality of the coach-athlete relationship on the variability of athletic performance. Findings from the first mixed factor model indicated that both athlete exhaustion at Time One and coach-athlete relationship quality at Time Two predicted the running distance covered by athletes during training session. The second mixed factor model revealed that performance on CMJs was predicted by athlete exhaustion at Time One, coach-athlete relationship quality at Time One, and the interaction effect between athlete exhaustion at Time One and coach-athlete relationship quality at Time One. The final mixed factor model indicated athlete exhaustion and the quality of the coach-athlete relationship did not predict the running distance covered by athletes during games. The results revealed that athletes who feel they are experiencing symptoms of emotional and physical exhaustion were likely to run further in training but not jump as high on CMJs. Furthermore, it could be suggested that athletes who perceive a high quality coach athlete relationship in terms of being close, committed and complementary were likely to have a lower CMJ score. Finally, the results may suggest that the coach athlete relationship acts as a protective mechanism when exhaustion is high to maintain CMJs performance. Chapter 7 discusses the general findings arising from the experimental Chapters, presents the central theoretical and applied implications, identifies the limitations of the research programme, and provides suggestions for future research.