The course emphasises the importance of circadian rhythms in regard to athletes and their performance. The neurophysiology and location of rhythm generators will be reviewed and their effects on the neuro-hormonal axis discussed. The ultradian rhythms, such as the alert-drowsy cycle, will be discussed in relation to performance. Sleep physiology and its stages will be discussed in relation to hormonal changes such as on diurnal changes in plasma cortisol and growth hormone. There will be discussion of jet-lag in relation to the phase changes due to rapid changes in longitude as occurs in airline travel. The effects of disordered sleep will be considered in relation to its effects on performance and related effects on arousal and attention and on hormones. Practical work will include observations in a sleep laboratory.