Jet Lag and Chronobiology
- •
The American Academy of Sleep Medicine defines jet lag as a syndrome involving insomnia or excessive daytime sleepiness following travel across at least two time zones. Jet lag is a syndrome of symptoms manifested by physiologic adaptations that occur when the body is shifted to a new time zone.
- •
Travel fatigue is a more complex combination of physiologic, psychological, and environmental factors that develop during travel; it may accumulate over the course of a season and reduce an athlete’s capacity to recover and perform.
- •
Chronobiology is the field of biology that examines cyclic phenomena in living organisms and their adaptation to solar- and lunar-related rhythms; these cycles are known as circadian rhythms .
Physiology of Jet Lag
- •
An average human experiences endogenous cycles of energy, mood, and activity that last approximately 25 hours.
- •
The primary pacemaker is the suprachiasmatic nuclei of the hypothalamus. When a traveler changes time zones, this pacemaker must undergo entrainment, which is the process of resynchronization with the new environmental light–dark cycle. Physiologic mechanisms involved in this process include:
- •
Melatonin, which is a hormone that is typically secreted at dusk by the pineal gland and helps the body anticipate the daily onset of darkness.
- •
Adenosine accumulates when a person is awake and causes progressive sleepiness.
- •
Adenosine accumulation is blocked by caffeine.
- •
- •
Direct neural pathway from the retina
- •
Blue wavelength light, in particular, can interfere with the sleep cycle.
- •
- •
Arginine vasopressin
- •
- •
Zeitgebers are environmental cues that help reset the pacemaker; these include: light, temperature, exercise, social interactions, and eating and drinking patterns.
- •
Disorders of circadian rhythm are most commonly experienced in the setting of a jet lag when a new sleep–wake cycle is required on entering a new time zone.
- •
Signs and symptoms of jet lag include changes in mood, headaches, digestive difficulties, and increased susceptibility to illness. Typically, athletes also suffer decreases in cognition, concentration, visual acuity, and memory. These changes often have adverse effects on physical and athletic performance.
- •
- •
The rate of adjustment to a new time zone is typically a day for each time zone crossed.
Prevention of Jet Leg and Travel Fatigue
- •
A structured athlete travel program that encompasses preflight, inflight, and postflight periods is the first step in establishing an effective approach to travel fatigue and jet lag.
- •
Because there is no physiologic adaptation with repetitive time zone transitions, each long-distance journey is unique and requires its own specific travel strategy based on the direction of travel, duration, and times of arrival/departure.
- •
By adopting a structured program and fatigue monitoring system, athletes and medical staff can help minimize travel-related physiologic and psychological issues, limit symptoms, and improve overall performance.
- •
Preflight component
- •
Although it may be difficult because of schedule restrictions, introducing a schedule within 7 days of travel is generally optimal.
- •
Consider gradually changing the sleep–wake cycle and meals to the new time zone by shifting an hour a day.
- •
Consider adjusting training to the destination time zone
- •
Avoid bright light for 2–3 hours before bedtime
- •
- •
An emphasis should be placed on getting enough sleep before travel to reduce sleep debt.
- •
- •
Inflight component
- •
If they have not already done so, advise athletes to adjust their schedule to be in sync with the destination time zone as soon as they board the plane to assist them in preparing for the destination (e.g., watches, meals, and sleep schedules).
- •
Maintaining appropriate hydration should be a priority.
- •
Avoid light-projecting devices, such as computers, tablets, and movies.
- •
- •
Postflight component
- •
The postflight period stretches 2–4 days or more beyond arrival. During this time, the activities of an athlete (including meals, sleep, rest, and recovery) should be strategically planned by the staff to accommodate rapid circadian adjustment.
- •
The most effective intervention in such situations is a combination of scheduled light therapy, light avoidance, and melatonin.
- •
Additional fatigue countermeasures include the judicious use of napping and caffeine, both of which can synergistically improve alertness and reduce symptoms of fatigue.
- •
Pharmacologic Measures
Melatonin : Melatonin supplements can aid in managing jet lag symptoms, both preflight and postflight.
- •
Preflight low doses (0.5–1.5 mg) of melatonin are most effective, whereas higher doses (3–5 mg) are recommended after flight.
- •
Pretravel melatonin may be used to gradually shift the feeling of dusk and bedtime to the anticipated time zone.
- •
Doses should be taken 30 minutes before bedtime on the night of travel and the initial 2–3 nights after arriving at the destination. This will mitigate sleep disturbances associated with jet lag while enhancing circadian adaptation.
- •
Sedatives: Athletes who do not suffer from jet lag or who do not respond to melatonin and experience 1–2 days of insomnia on arrival will likely benefit from the use of a traditional medium-acting (20–30 minutes) or medium half-life (6 hours) sedative (e.g., eszopiclone or temazepam). Very-short-acting (<15 minutes) and short half-life (4 hours) sedatives (e.g., zaleplon or zolpidem) can be useful for sleep during the flight. However, caution must be exercised with inflight use of sedatives because this may increase the risk of deep vein thrombosis (DVT) and decrease responsiveness in the event of an inflight emergency. Use of sedatives may be considered illegal in certain sports without a therapeutic use exemption waiver.
Stimulants: Caffeine and other stimulants (e.g., modafinil) may be useful in combating fatigue. However, use of stimulants may be illegal for some athletes without a therapeutic use exemption waiver.
- •
Caffeine: The strategic use of caffeine (e.g., a 50–200-mg pill or beverage) in combination with a 15- to 30-minute nap has been shown to be effective in improving cognitive function in sleep-deprived states and at the lowest point of the circadian cycle. Athletes should be cautioned that caffeine above certain levels is often considered illegal by doping codes and may result in suspension, loss of medals, and vacation of victories.
- •
Nonpharmacologic Measures
Preadaptation and light therapy: Light exposure is the primary cue for circadian rhythms. Exposure to bright light of adequate intensity and duration can advance or delay circadian rhythms based on the timing of exposure. Bright light exposure in the morning will help advance the body clock, while exposure in the late evening will help delay it. Attempts to shift circadian rhythms with preflight exposure to bright light before departure have been successful during both eastward and westward travel. Exposure to natural bright light promotes circadian shifts. Avoidance of bright light, particularly short wavelength, blue light in the evening may help with shift for eastward travel. Use of blue blocking glasses, such as amber safety glasses, may diminish this exposure. Athletes should be cautioned to avoid evening use of tablets, computers, televisions, and mobile phones in order to minimize blue light exposure.
Sleep: Sleep can be used to acclimate or adjust an athlete’s circadian rhythm before travel or decrease symptoms of sleepiness upon arrival. Shifting the sleep schedule 1–2 hours toward the destination time zone in the days preceding departure may shorten the duration of jet lag. In addition, strategic napping has been discussed as a potential method to mitigate the symptoms of jet lag. The best time to nap (inflight or postflight) is nighttime in the destination time zone. “Power naps” (20 minutes) do not result in sleep inertia and may decrease daytime sleepiness in individuals experiencing jet lag. However, naps of >20 minutes may delay sleep adaptation and slow resynchronization.
Deep Vein Thrombosis (DVT) and Travel
- •
DVT is a condition wherein a blood clot develops in the deep veins, most commonly in lower extremities. A part of the clot has the potential to break off and travel to the lungs, causing a potentially life-threatening pulmonary embolism (PE).
- •
Prolonged periods of inactivity caused by space limitations may diminish circulation and produce lower extremity edema. Prolonged sitting with bent knees compresses the popliteal veins, which is another potential risk factor for clot formation.
- •
- •
“Economy class syndrome”: Long-distance air travel has been associated with a 2–4-fold increased risk of venous thromboembolism (VTE), including DVT.
- •
Environmental factors in flight, such as low oxygen, low humidity, and low cabin pressure, contribute to dehydration, which concentrates the blood; this effect is worsened when passengers consume alcohol or do not adequately replenish fluids lost due to dehydration. However, there is no evidence that dehydration is directly associated with VTE.
- •
Certain reports have suggested that flights of ≥8 hours increase the risk of VTE in the presence of additional risk factors in a patient.
- •
Other risk factors include age over 40 years, obesity, and estrogen use.
- •
Athletes and individuals in general good health are at a lower risk of VTE.
- •
- •
A DVT most often originates in the calf, with persistent cramping or “charley horse” that intensifies over several days. This pain may be accompanied by leg swelling and discoloration.
- •
In most cases, travel-related VTE occurs in the first 1–2 weeks after travel. The risk returns to baseline after 8 weeks.
- •
Treatment: early detection and anticoagulant drugs (e.g., heparin, low-molecular-weight heparin, warfarin: see Chapter 31 , “Hematologic Problems in Athletes” for additional details)
- •
Prevention: maintaining hydration, exercise, and wearing support stockings may help decrease the overall risk. Periodic activity, approximately every 2 hours, can include isometric exercises, walks along the aisles, or stretching exercises. Below-the-knee graduated compression stockings that provide 15–30 mmHg of pressure have been advocated as a preventive measure. Drugs such as aspirin have antithrombotic properties but are not recommended as a prophylactic measure in otherwise healthy individuals.
Related posts:
Stay updated, free articles. Join our Telegram channel
Full access? Get Clinical Tree
