Symptoms
The symptoms of jet lag can be quite varied, depending on the amount of time zone alteration, time of day and the susceptibility of individual differences. Sleep disturbance occurs, with poor sleep upon arrival, sleep disruption including trouble falling asleep (if flying east), early awakening (if flying west) and interrupted sleep with multiple awakenings and trouble remaining asleep. Cognitive effects include poorer performance on mental tasks and concentration, increased fatigue, headaches, and irritability, and problems with digestion including indigestion, changes in the frequency of defecation and consistency of feces and reduced interest in and enjoyment of food. Symptoms are caused by a circadian rhythm that is out of sync with the day-night cycle of the destination. Jet lag has been measured with simple analogue scales but a study has shown that these are relatively blunt for assessing all the problems associated with jet lag. The Liverpool Jet lag Questionnaire was developed to measure all the symptoms of jet lag at several times of day, and this dedicated measurement tool has been used to assess jet lag in athletes.
Jet lag usually requires a change of three time zones or more to occur, though some individuals can be affected by as little as a single time zone or the single-hour shift of daylight saving time. Symptoms and consequences of jet lag can be a significant area of concern for athletes traveling east or west to competitions as performance is often dependent on a combination of physical and mental characteristics that are impacted by jet lag.
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