About the disturbances of the normal human circadian rhythms by travelling across multiple time-zones and how to minimize them: Travelling across multiple time-zones disturbs the normal human circadian rhythms and induces the syndrome known as jet lag. Symptoms include fatigue, difficulties in sleeping at the right time, loss of motivation, appetite, headache and periodic head-buzz.These effects are transient and disappear once rhythms are re-attuned to the new local environment. There are circadian rhythms in many components of tennis performance that broadly correspond to the 24-hour changes in bodytemperature. These performance rhythms are disturbed after trans-meridian flights. Effects tend to be worse after flights to the east rather than the west, because the body clock adjusts more easily when a phase delay rather than a phase advance is required. It seems that the sleep-wake cycle must first adjust to the new environment before the normal body temperature curve reappears and jet-lag symptoms disappear. Various treatments for alleviating jet lag have been proposed. Adjusting the sleep-wake cycle prior to travelling is of marginal benefit only, and an adjustment of more than 2 hours (in the appropriate direction) is not recommended. Periodic activity during flight (isometric exercises in one`s seat, light stretching exercises at the back of the plane) is advised to reduce stiffness. Extra fluid intake is encouraged to counteract a gradual loss of water due to the pressurised dry air on board. On arrival, attention to lifestyle is a key to taking advantage of the main signal that governs the body clock. Avoiding light in the morning after an eastward flight and actively seeking stimulation (natural light, moderate exercise, social activity) during the evening after flying westward are helpful. The timing of meals is more important than seeking an anti-jet lag diet. The use of chronobiotic drugs can be counterproductive when multiple time zones are crossed. The British Olympic Association has issues a Position Statement on use of melatonin and sleeping pills (Reilly et al., 1998) which is guarded but acknowledges that some of its athletes use hypnotics. Jet lag symptoms are compounded when heat stress is combined with gruelling travelling schedules. Monitoring of changes in body mass, urine colour and osmolality can help in identifying individuals with low hydration status.
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