This post discusses the science explaining jet lag and the strategies we can use to help reduce its effects when travelling.
Having recently crossed eleven time zones to travel between the UK and Australia it goes without saying that I suffered from jet lag! However, jet lag can be significantly reduced through behaviour and the use of natural cues. These can be used to assist travel for everyone but particularly with athletes when sporting performance can be impaired.
Why Does Jet Lag Occur?
Jet lag occurs from a desynchronisation between the internal circadian rhythms (‘body clock’) and external environmental conditions, caused by transmeridian travel (across time zones). For as long as the body remains out of phase with the local environment, normal body rhythms in hormones, core temperature and the sleep cycle are affected.
It is estimated that for every hour time zone crossed, a day is needed for the body to adapt naturally. Eastward travel causes problems falling asleep at bedtime since the new ‘night’ occurs during the body clock’s daytime while travelling westward extends the length of the day allowing the body to catch up.
The body uses external factors called ‘zeitgebers’ (‘time-givers’ in German) to resynchronise the circadian clock daily, so we can use these cues to speed this adaptations and induce a phase advance or delay effect. The principal zeitgeber is natural sunlight although artificial light can also exert influence.
It is estimated that for every hour time zone crossed, a day is needed for the body to adapt naturally.
Melatonin is a hormone secreted by the body during the hours of darkness to induce sleep and can be administered before and during travel to help shift the circadian clock. However, in the UK the drug Circadin is prescription only and its use is not recommended by the World Health Organisation. Exercise, eating and drinking patterns and social interactions are also forms of zeitgebers.
It is important to note the differences between jet lag and travel fatigue. Tiredness and weariness that results from the disruption of travelling regardless of time zones accompanies every journey and is known as travel fatigue, so includes northwards/southward travel within time zones. Jet lag is an additional component when travelling across time zones and induces different symptoms.
Practical Strategies to Reduce Jet Lag
Now we understand why jet lag occurs and the zeitgebers that we can influence to speed the process, how can we programme these interventions?
Work out time differences between the departure and destination locations including any stopovers.
Pre-flight adaptations can be incorporated in the few days leading up to travel although care must be taken in sport to not cause a detriment to performance before travel. Training, meal and/or sleep times can be adjusted to start to move closer to the destination time zone.
Adjust watches to the destination time zone as soon as you enter the plane
Maximising in flight health is essential; use stretching and walks to reduce thrombosis, maintain hydration with water and juices therefore avoiding alcohol and fizzy drinks, maximise sleep quality with comfortable environment and minimise electronic devices, try to align meals and sleep time with the destination time zone
Pharmacological interventions are somewhat controversial so seek expert advice on these (melatonin, sleeping pills).
If you have control of the trip logistics and the flight times, plan around the good and bad local times for light exposure to promote phase advance or delay as required. (See Reilly et al, 2005 for more detail)
There is individual variation in response to jet lag so some will take longer than others to adapt.
Case Study Example
Let’s take a practical example of a trip from the UK to Japan. Firstly, compile the time difference and daylight times for both the UK and Japan during the period of travel (here shown for December):
Japan Sunrise | Japan Sunset | UK Sunrise | UK Sunset |
06:39 – 06:44 | 16:30 – 16:32 | 07:54 – 08:01 | 15:51 – 15:52 |
Calendar of Dates (local times highlighted)
Sat 8th | Sun 9th | Mon 10th | Thurs 13th | |
Match | Fly | Land | Match | |
UK | 5pm | 6pm | 6am | 10am |
Japan | 2am | 3am | 3pm | 7pm |
You can use tables such as these to plan the logistics.
Some of the key considerations are given below:
Pre adjustment is suggested to help minimise jet lag i.e. create small shifts in the circadian clock in the few days preceding the trip. However, I would not want this to interfere with the performance in the match the day before travel but could suggest an earlier bed time on the Saturday night after the game and earlier wakeup call on the day of travel (travel permitting). The touring party could be encouraged to see daylight on the mornings of the Saturday and Sunday to start to advance circadian rhythms.
Optimal hydration and carbohydrate recovery should be particularly emphasised post match on Saturday to ensure the body’s fuel and fluid stores are replenished for travel.
Arriving in Japan at 3pm local time (6am UK time) and should be immediately exposed to natural sunlight. However, according to daylight hours there is only one and a half hours remaining before the sunsets at 4:30pm local time therefore no napping (or sunglasses!) should be permitted during any onward transfers.
The local night time in Japan will occur in the hours of daylight back home but the travelling party should be encouraged to try to align bed times with local times. The athletes should be encouraged to eat a carbohydrate rich evening meal on the first night to release serotonin that can help induce sleep. Pharmacological interventions could be used at the discretion of each individual.
With a 9 hour time difference to the East it is important to try to promote a phase advance. Using natural light as the stronger zeitgeber the travelling party should be exposed to daylight in the early afternoon, although local time morning exposure may delay the body clock (i.e. feel like staying up later in the UK).
It is important that training times are planned by taking into account the good times for local light exposure but balanced with the increased injury risk of training whilst suffering from jet lag. In this example training could be aligned with the match at 7pm local, fitting nicely with the 10am UK time, but it is essential the travelling party are still exposed to daylight given that training will fall after sunset. Perhaps training times can be staggered as the body clocks adapt.
For further reading please see:
Reilly, T., Atkinson, G., Edwards, B., Waterhouse, J., Torbjorn, A., Davenne, D., Lemmer, B. & Wirz-Justice, A. (2007) Coping with jet-lag: A position statement for the European College of Sport Science. European Journal of Sport Science. 7(1) pp1-7
http://www.chronobiology.ch/wp-content/uploads/publications/2007_10.pdf
Reilly, T., Waterhouse, J. & Edwards, B. (2005) Jet lag and air travel. Implications for performance. Clinics in Sports Medicine. 24, 367-380
Samuels, Charles H. 2012. Jet Lag and Travel Fatigue: A Comprehensive Management Plan for Sport Medicine Physicians and High-Performance Support Teams. Clin.J.Sport Med. 22(3): 268-273