Aquatic athletes participating in international competitions often have to deal with the effects of long distance air travel and changing time zones. Long distance flights can cause changes in circadian rhythms and the sleep-wake cycle. For many athletes, this leads to jet lag, a condition characterised by sleep loss, headaches, dizziness, fatigue and reductions in energy, alertness and overall thinking.
Circadian rhythms are internally driven variations in an individual's biological and behavioural functions that cycle over roughly a 24-hour period. They can be modified by bright light, darkness, the hormone melatonin, and exercise, but the light-dark cycle of the environment seems to have the strongest influence.