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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.
Does Jet Lag Reduce Sports Performance?
While there is no research definitively stating whether or not jet lag reduces sports performance, it is likely that the symptoms of jet lag can result in decreased sports performance due to both physiological and emotional factors. Feeling fatigued is clearly not the optimal mindset in which to perform at one's best. Despite a clear link between jet lag and decreased performance still being unproven in the scientific literature, many athletes choose to "reset" their circadian rhythms to match the time zone of their destination city prior to competition.
JET-LAG: Symptoms and Treatment
The feelings of disorientation encountered as a result of crossing time zones are known as jet lag. Symptoms include fatigue and general tiredness, inability to sleep at night, loss of concentration, decreased motivation, headaches and general malaise. Jet-lag occurs when biological rhythms are disrupted as a result of rapid transitions across multiple time-zones. The same symptoms are seen with nocturnal shift work employees who transfer from day to night shifts.
Disruption in normal Circadian Rhythms
Following a journey across multiple time zones the body's rhythms at first retain the characteristics of their point of departure. However, the new time zone forces new influences on these cycles, the main factors being the time of sunrise and onset of darkness.
The body attempts to adjust to the new destination but core temperature is relatively sluggish in doing so. As a rough guide it takes about one day for each time zone crossed for body temperature to adapt completely. The individual may have difficulty in sleeping for a few days, but activity and social contact during the day help in accelerating the adaptations of the arousal rhythm. Thus arousal adjusts more quickly than does body temperature to the new time zone. Until the whole spectrum of biological rhythms adjusts to the new local time, the performance of exercise may be below par.
Allowing for individual differences, the severity of jet lag is affected by a variety of factors. In general, the greater the number of time zones crossed, the more difficult it is for the athlete to cope. A 2-hour phase shift may have marginal significance but a 3-hour or greater time shift will cause increased symptoms in the athlete. In such cases the flight times time of departure and time of arrival - may determine the severity of symptoms.
The severity of symptoms may be worse 2-3 days after arrival than on the day immediately following arrival. Symptoms then gradually abate, but can still be acute at particular times of day. There will be a window of time during the day when the period of high arousal associated with the time zone just left overlaps with the arousal high point at the new local time. This window may be predicted in advance and should be utilised for timing of training practices in the first few days at destination.
The direction of travel affects the severity of jet lag. It is easier to cope with flying in a westward direction compared to flying eastward. In flying westward the normal cycle is temporarily lengthened and body rhythms can extend period of about 27 hours rather than 24 hours and thus catch up. When time zone shifts approach the maximum 12-hour change, there may be little difference between eastward and westward travel.
The direction of travel can be a relevant consideration. When going eastward the mean performance is depressed more and the peak performance declines more dramatically than is the case on travelling westward. The reason that westward travel is easier occurs because the natural period of circadian rhythms is greater than 24 hours, so each rhythm adapts more quickly when the day is artificially lengthened. Altering training times for a few days prior to travel to take into consideration the time of competition in another time zone is known to be beneficial.
Young individuals have a better tolerance to a change in time zones, owing to a better regulation of biological clocks. Physical fitness also seems to play a role: active subjects demonstrate higher amplitudes in existing rhythms than age-matched controls, a difference indicative of superior regulation. But other than these factors, there has been little success in attempting to predict good and poor adapters to long haul flights. Furthermore, the fact that an individual escapes lightly from symptoms on one occasion is no guarantee that he or she will do so again on the next visit.
How athletes can reduce the effects of jet lag on performance in the aquatic sports
Shifting Circadian Rhythms
There is some evidence that supports the idea that circadian rhythms can be modified by being exposed to bright light and darkness, taking low dose melatonin supplements, and exercising at certain times of the day. Of the three, exposure to bright light seems to have the strongest influence on sleep-wake patterns.
If it is possible to do so, flights should be scheduled so that athletes arrive well in advance of competition. One day for each time zone crossed does leave a cushion of safety, even travelling eastward. The time for adaptation may be shortened by exploiting the external factors that reset biological clocks: rest/exercise, darkness/ light, meals and social influences. The key is to tune in straight away to the external influences of the new environment.
Before and During Travel
On lengthy journeys it is unlikely that any manoeuvres will eliminate jet lag, but with careful planning the symptoms can be attenuated. In the week prior to departure it may be possible to adjust the time of arising and going to bed, the adjustment depending on the direction of flight. An alteration of more than two hours is likely to be unproductive, since this would interfere with the pattern of social and domestic engagements during the day. Besides, the major synchroniser of human circadian rhythms - natural daylight - remains the same.
Once flight times are known, a routine on the plane may be planned. In day time flights it will be necessary to stay awake, keep mentally active and perhaps watch the in-flight movie. On long haul flights that entail travelling during the night it will be necessary to get some sleep on the plane. The timing of this should be decided in advance so that some meals on board can be missed. Transit or transfer episodes en route should be taken into consideration. It is a good strategy to set one's watch to local time at the next point of landing, once on board the plane: in a single haul flight this would be the local time of the country of destination. The important thing is that the traveller mentally tunes in to the new local time straight away and adjusts behaviour accordingly.
To compensate for the dry air on board flight, copious rehydration is advised. Fruit juices are best, fizzy drinks should be avoided. Alcohol should not be taken, since it acts as a diuretic (increases urine production) and also affects the normal circadian rhythm in kidney function. Caffeine in coffee also stimulates water loss, and its arousal effect on the central nervous system means it should not be taken if sleep is desired. One suggestion is that the last meal prior to the time allotted for sleep should be high in carbohydrates and low in protein in order to induce drowsiness. Carbohydrates are the building blocks of serotonin, a neurotransmitter that regulates sleep. Caffeine and a low-carbohydrate high-protein breakfast would help raise the level of arousal and prevent a relapse into sleep.
Athletes may feel stiff or cramped because of their restrained posture on board flight. They can perform isometric exercises for arms, trunk or legs while in their seats. It is even better to walk down the aisle of the plane and occasionally do flexibility or stretching exercises at the back of the plane.
Sports teams have used sleeping pills to induce sleep while on board. Although such drugs as benzodiazepines, as well as the newer agents, Zopiclone/Zolpidem (brand name Imovane in Canada Zolpidem in the USA, and Zimovane in the UK) is a non-benzodiazepine sleeping agent used in the treatment of insomnia. The Benzodiazepines, as well as these newer agents, are effective in getting people to sleep, they do not guarantee a prolonged period asleep. Besides, they have not been satisfactorily tested for subsequent residual effects on motor performances such as sports skills. They may also be counter-productive if administered at the incorrect time. A prolonged nap at the time the individual feels drowsy (presumably at the time that he or she would have been asleep in the time zone departed from) simply anchors the rhythms at their former phases and so resists the adaptations to the new time zone.
Strategy upon Arrival
On reaching the country of destination a key factor is to fit in immediately with the phase characteristics of the new environment. Athletes should already have worked out the local time for their departure. There may be other environmental factors to consider such as heat, humidity or even altitude.
Having travelled westward, athletes may be allowed to retire to bed early. Early onset of sleep will be less likely after an eastward flight. In this case a light training session on that evening would be helpful in instilling local cues into the rhythms. Besides, there is some evidence that exercise does speed up the adaptation to a new time zone.
For the first few days in the new time zone, training sessions should not be all-out efforts. Skills requiring fine co-ordination are likely to be impaired and this might lead to accidents or injuries.
In this period of adaptation the athlete should eat evening meal largely high in carbohydrates. These would include vegetables with a choice of chipped, roast or baked potatoes, pasta dishes, rice and bread. These should include sufficient fibre to safeguard against constipation.
In the early days in the new country athletes should be discouraged from taking prolonged naps. A nap at the time they would have been asleep had they stayed at home would make subsequent sleep more difficult and retard the adjustment of the major biological clocks to the new regimens. Exposure to bright light, preferably natural daylight is a useful antidote to drowsiness in such circumstances.
Taking drugs can alter biological clocks, depending on the time they are taken. Caffeine (in coffee) and theophylline (in tea) are stimulants of the central nervous system. Taken in the evening they would help in recovery after flying eastward and in the afternoon after flying westward.
Administration of melatonin, which is a naturally occurring hormone in pineal gland, can be a helpful with regaining the circadian rhythm. Some evidence supports the idea that the circadian cycle may be delayed by taking a low dose (0.5 mg) of melatonin between morning and mid-afternoon hours, and that the cycle can be advanced by taking melatonin between mid-afternoon and bedtime.
For athletes exercise is a powerful way to overcome jetlag. It is recommended, even on the day of arrival, except late in the evening local time. Exercise at a light intensity is adequate for stimulating resynchronisation of rhythmic characteristics as exercise that is too strenuous may disrupt rather than promote sleep.
The International Federation of Sports Medicine issued guidelines for athletes who travel across time zones for competition. Here is a summary of their recommendations:
1. Bright light and darkness has the most direct influence on shifting circadian rhythms
2. Melatonin may also influence the circadian cycle and be of great use when the athlete travels.
3. Exercise, one to three hours, may induce significant circadian phase shifts.
4. Flight Plans for an athlete should be done well in advance to reduce anxiety in stressful situation.
5. During a Flight stay hydrated, limit alcohol and caffeine, stretch, walk and stretch.
Upon arrival consider using appropriately timed bright light, melatonin, or exercise to shift circadian rhythms.
* Dr. Sandra Soldan graduated in 1997 from the Federal University of Rio de Janeiro and then dedicated ten years to Triathlon. She attended the Sydney 2000 and Athens 2004 Olympic Games and three Pan-American Games. She won the Aquathlon ITU World Championship in 2002 and remained ranked in the top 5 athletes in the World in the ITU ranking in 2001.
After the Pan-American Games in Rio 2007 she returned to Medicine, and did a post graduate degree in Sports Medicine. Most recently, she started working in doping control at the CBDA (Brazilian Swimming Federation) and Brazilian Anti-Doping Agency.