Acute sleep deprivation has been demonstrated in some studies to have small disruptive effects on basal hormonal concentrations [30, 31]. Although salivary cortisol appeared to be elevated with sleep deprivation, this result

did not reach statistical Fedratinib significance. Interestingly the higher dose of caffeine was associated with significant elevation in pre-trial cortisol, but not testosterone. High doses of caffeine have previously been demonstrated to acutely increase cortisol and, to a lesser extent, testosterone [20, 32]. Whether such elevations have any significance in outcome is unknown. Cortisol is associated with AZD8186 clinical trial arousal but also with anxiety [33]. Unfortunately we did not concurrently measure salivary alpha amylase in this study, which may also be a useful marker with respect to system arousal [34]. Testosterone was unaffected by sleep deprivation and by all treatments except the high dose of creatine, where there was a trend towards higher concentrations. We do not have useful speculation as to why this increase was seen, although it was across all subjects. Still, the increase was

relatively small in magnitude and we doubt at this stage that it has any real physical or behavioural consequence. As we used saliva measures we cannot rule out some local oral cavity artefact effect of creatine. Free testosterone levels have, however, been RSL3 nmr linked to intra-individual variance in short timeframe muscular power [35], and long-term creatine supplementation has been reported as influencing testosterone metabolite pathways [36], so the observation is perhaps worthy of some follow-up. Little has been published on acute creatine use as it has primarily been regarded as a longer term supplement to muscular function gain. In terms of brain

and behavioural function it would appear it have some acute effects of value. It is also possible that the observed effects of caffeine and creatine reported in this and other studies are potentially summative and thus, would seem mafosfamide a logical progression for research. Conclusions We observed a significant effect of acute sleep deprivation on performance (on both dominant and non-dominant passing sides) of a repeat simple skill test in elite rugby players. The deficit in performance with sleep deprivation was addressed by acute supplementation with either caffeine or creatine. In both cases, the two dosages tested had similar effects on skill performance. Both may offer practical and viable options prior to training and competition to assist skill performance when sleep loss has occurred. Acknowledgements We acknowledge with gratitude the professional athletes that contributed to this study. In part this study was supported by grants (ESPRIT) from Engineering and Physical Sciences Research Council UK and by UK Sport Council. References 1.