Sleep is considered an essential component of athlete health, post-exercise recovery and performance. Sleep in athletes is a novel and vital area of sports science. Despite the importance of sleep in athletes, relatively little is known in this field, both in New Zealand and globally. The overall aim of this PhD was to characterise sleep in elite collision sport athletes, develop and apply interventions to improve their sleep quantity and quality, and investigate resultant recovery and performance benefits.

Study one investigated indices of sleep and sleepiness using qualitative methodology (Chapter three) and revealed a high prevalence of poor sleep quality, sleepiness and obstructive sleep apnoea (OSA) risk factors in collision sport athletes. Indeed, one in two athletes scored as ?poor sleepers? with the Pittsburgh Sleep Quality Index (PSQI) and one in three athletes reported clinically significant daytime sleepiness. Furthermore, the prevalence of clinically suspicious OSA (8%) was twice that of the general population. With an understanding of sleep behaviour among elite collision sport athletes, and a growing appreciation that their risk of poor sleep is high, Chapter four expanded upon qualitative methodology to investigate the recovery-stress state within the same cohort of athletes. The Recovery-Stress-Questionnaire for Athletes (RESTQ-Sport) was used to establish relationships between validated measures of sleep quality and sleepiness and various RESTQ-Sport subscales, including sleep quality. Specifically, a moderate negative relationship between the PSQI score and RESTQ-Sport sub score of sleep quality was observed (-0.49; ? 0.10). Furthermore, there was a moderate relationship between the PSQI score and RESTQ-Sport sub score of lack of energy (0.36; ? 0.11) and a small relationship between the ESS score and RESTQ-Sport sub score of fatigue (0.11; ? 0.13). Results suggest that the RESTQ-Sport can adequately assess sleep quality in athletes, although the addition of validated sleep questionnaires such as the PSQI and ESS, alongside the RESTQ-Sport, may provide coaches more thorough information about an athletes sleep based recovery. Furthermore, additional comprehensive sleep monitoring may be most pertinent during hard training phases.

Chapter five built upon the qualitative findings of the previous two studies. A six week pre-post control-trial intervention study was conducted with the aim of further characterising measures of sleep in professional rugby players using quantitative methodology (sleep monitors). Following a control phase, where baseline sleep, immune function and stress hormone data was observed, this study applied a three week sleep extension intervention during a pre-season training block. The efficacy of a sleep education programme and sleep extension in improving sleep quantity and quality and markers of physical stress, immune function and performance was evaluated. Results from the control phase further demonstrated that collision sport athletes experience poor sleep quality, which declined further during an intensive training phase, with a concomitant rise in stress hormone levels. The sleep extension intervention elicited a significant, moderate (-0.65; ? 0.99) improvement in the percentage change in sleep quality scores compared to the control (-24.8 %; ? 54.1 %) A greater time in bed (7.3 %; ? 3.6 %) and total sleep time (6.3 %; ? 6.3 %) was observed after sleep extension, with a moderate (0.84; ? 0.42) and small (0.46; ? 0.46) difference in the changes between groups, respectively. Sleep extension also mitigated a small (-0.40; ? 0.45) rise in cortisol levels (-18.7 %; ? 26.4 %) and small (-0.44; ? 0.31) resultant improvements in reaction times (-4.3 %; ? 3.1 %) were observed. These results suggest that implementing a sleep extension programme with elite athletes can be worthwhile and should be considered for inclusion by elite athletic programmes.

Finally, the efficacy of consuming a tart cherry juice concentrate (TC) for improving sleep and indices of recovery and performance during an off season training period were investigated (Chapter six). The effect of TC on measures of sleep and daytime sleepiness, fatigue and muscle soreness were inconclusive. However, the TC intervention demonstrated a decrease in inflammation represented by C-Reactive Protein (C-RP) concentration (-8.5 % ? 97.3 %) compared to an increase in the placebo group (119 % ? 174 %), with a moderate difference in the change in C-RP between groups (-0.98; ? 1.16). Results suggest that TC may be applied to mitigate increases in inflammation in highly trained rugby players, and there may be a dose dependent relationship with sleep quality. Tart cherry juice supplementation may provide collision sport athletes in particular an adjunctive strategy to enhance recovery alongside sleep extension. Further research is required to establish both a minimal effective TC dose and to fully realise the potential of TC supplementation for sleep, recovery and performance benefits.