– Written by Dina C Janse Van Rensburg, Audrey Jansen van Rensburg and Martin P Schwellnus, South Africa

INTRODUCTION

Global travel and international compe-tition are inevitable for the modern-day athlete and sports team. Jet lag can cause disarray for the individual athlete as well as for the whole team. Jet lag is caused by rapid transmeridian travel across different time zones, and is generally considered as a syndrome where the internal body clock is out of sync with the destination time zone. Its impact depends on the duration and direction of flight, the flight schedule, and individual differences. Jet lag tends to be transient and can result in physiologic disturbances and a complicated set of physical symptoms^1,2 .

Furthermore, in the short-term, at the new location, the traveling athlete is exposed to diverse allergens or strains of pathogenic organisms, unfamiliar environmental con-ditions (temperature, humidity, altitude, pollution), and variation in diets that may lead to a higher burden of illness^3,4.

Knowledge regarding the preparation and management strategies to assist travelling athletes and teams are therefore essential for the accompanying physician and support staff. The aim of this article is to firstly equip the travelling athlete and -team with a methodical approach during the pre-travel-, flight- and post-travel periods in order to minimise the effects of jet lag^1,2and to secondly give practical advice on strategies to manage the risk of illness during traveling – protecting athlete health^3,5,6.

A. THE MANAGEMENT OF JET LAG INCLUDES PRE-TRAVEL, IN-FLIGHT JOURNEY, AND POST-TRAVEL PERIODS

Pre-travel period:

Pre-travel strategies to mitigate jet lag can be complicated due to the athletes’ constrained schedules and limited options of flight selections⁷. Choice of flight-times and the period of layover when travelling will assist with effective adaptation^1,8,9.

In the seven days prior to travel, modified training routines with reduced training volume and intensity should be adopted⁷, and the adjustment of training times to the destination time zone can be considered. Adequate sleep (typically defined as six to eight hours per night) is important and several studies have highlighted that good sleep results in better sports performance^10-14. Sleep debt should therefore be reduced to the minimum. Evidence also exists that shifting the sleep schedule at one hour per day towards the destination time zone is effective to assist with phase advance or -delay, but may be impractical^7,15.

Pre-departure pearls include:

·     Get enough sleep to avoid sleep deprivation (six to eight hours per night).

·     Reduce training volume & intensity (seven days prior to departure).

·     Consider travel schedules, to assist sleep-wake cycle .

·     Shift bed- and mealtimes one to two hours earlier before travelling east & one to two hours later before travelling west to adapt to local time at the new destination time zone (effective pre-adaptation). 

During journey:

The in-flight management period of the journey is crucial for recovery and adaptation, and to prepare for the destination. A few factors need to be considered, including travel fatigue and jet lag, hypoxia due to reduced cabin pressure and infection risk due to the confined environment. 

In a study by Waterhouse et al², individuals with a short interval between their last full sleep before their flight and their first one at their destination, had less jet lag than those whose interval between full sleeps were longer. Physicians can also strategically use sedatives and/or melatonin to facilitate sleep, but only if athletes have used these substances before. 

During journey pearls to mitigate travel fatigue and jet lag include¹:

·     Comfortable shoes and clothing.

·     Avoid large meals. 

·     Keep hydrated.

·     Avoid alcohol and caffeine.

·     Adjust watch to destination time.

·     Maximum rest/sleep.

·     Follow sleep/wake pattern of desti-nation.

·     Minimal distractions (e.g. electronic devices). 

·     Stretch and walk when awake. 

Physical performance may not only be impacted by circadian rhythm disruption, but also by hypoxia suffered during airline travel. During routine commercial flights the cabin is only pressurised to a reduced atmospheric pressure of 2438 m altitude, resulting in a decrease of arterial oxygen partial pressure (PaO₂) from 95 mmHg to 60mmHg, and a 3–4% decrease in systemic oxyhaemoglobin saturation. This may lead to mild hypoxia¹⁶. It is plausible to consider that time spent on long-haul flights should be seen as time spent at altitude with similar consequences^17-18. Furthermore the cabin is a closed environment with fellow passengers and specific areas like tray tables posing a high risk for infection^19-21.

During journey pearls to mitigate hypoxia and an increased risk of infection²⁰:

·     Understand the impact of lower cabin air humidity, altitude and hypoxia in the athlete.

·     Beware of seat location or contact areas for infection risk and take prevention (Also refer to section on protection of athlete health, and specifically Table 5):

·       sitting in an aisle seat, 

·       proximity to ill passengers, 

·       contact areas: head rest, tray tables, arm rests, seat controls, seat belt buckle, toilet flush button, bathroom stall lock, drinking fountain buttons, etc.), 

·       overhead air vent.

Post-travel (at destination):

The post flight period of substantial jet lag disturbance extends from two to four days on arrival. During this time, the athlete’s activities (including meals, sleep, rest, and recovery) need to be strategically planned by the support team to accommodate rapid circadian adjustment. The direction of travel is very important as, in most individuals, the body’s circadian rhythm is naturally longer (approximately 24.2 hours) than the set 24-hour light–dark cycle of one day. As a result, it is easier for individuals to adapt to a longer day than to a shorter one^22-24. The impact of travelling eastward is therefore more detrimental than travelling westward for most individuals. The fastest rate of adapting to the new destination time zone is approximately half a day per time zone crossed when travelling west, or 1 day per time zone crossed when travelling east^7,22,25.

The direction of travel may also have implications for training and preparation for matches. A hypothesis related to circadian rhythm of performance is that performance peaks in the evening, and the time of competition may be a critical factor affecting performance post-travel. Winter et al reported that in early afternoon baseball competitions, the teams travelling east-to-west will have a disadvantage over time zone adapted teams in the west, since the game would occur closer to the travelling team’s local bedtime²⁶. 

Furthermore, travelling between the northern and southern hemispheres causes disorientation due to changes in winter-summer climate and a shift in timing (sunrise and sunset). Travellers also experience variation in natural lighting and the amount of solar irradiation with seasonal changes – predominantly during mid-winter/mid-summer when light variances are greatest and less in autumn/spring². 

Due to circadian rhythm disruption, the traveling athlete may in the short-term be exposed to sleep disturbances, a change in mood and fatigue levels and a possible higher burden of illness and injury. However, additional research is needed to support this. The duration and severity of symptoms experienced by the individual athlete, depend on the number of time zones crossed²⁷, and the direction of travel¹⁸. This may potentially have a negative impact on physical performance^28,29as is explained by Figure 1 and further discussed in Table 1. 

Optimising the timing of interventions to counteract jet lag is complicated by some challenges:

The circadian phase is synchronised to the local solar light–dark cycle and promotes alertness during the day, and sleep at night. The challenge remains to determine the best timing of an intervention for circadian re-entrainment after time-zone shift⁹. In the clinical setting several measures are currently used to evaluate the human circadian system. These include wearable wrist-watch accelerometer, melatonin and cortisol biomarkers (hourly urine, saliva or blood samples for 1 to 2 days) and core body temperature measurement (rectal probe, oesophageal probe or ingested telemetry pill monitoring)^30-34.

There are significant intra- and inter-individual variation in the ability to tolerate circadian phase misalignment. An individual’s chronotype preference (evening-types vs morning-types) may affect their travel responses, and adaptation rates to eastward and westward travel^32,35. Chronotype is partly influenced by our environment, but the differences in circadian rhythms are also linked to individual genetic variances^36-39.

Incorrect timing of interventions may induce a phase-shift in the wrong direction and pharmacologic interventions may cause side effects. 

Management strategies for jet lag:

A combination of scheduled light therapy, light avoidance, and melatonin therapy can be implemented as fatigue countermeasures¹. The phase shifts of the body clock (advance and delay) created by light and exogenous melatonin ingestion at different times during the day is illustrated in Figure 2. 

Additionally, the careful use of a nap that coincides with the circadian nadir (lowest point in each 24-hour cycle) to reduce cumulative sleep debt and consequent fatigue, and caffeine according to each individual’s need can improve the alertness of the athlete and reduce symptoms of fatigue. 

Effective management strategies that are described in scientific literature, can be divided into pharmacological and non-pharmacological interventions, and are summarised in Table 2.

Post-travel (at destination) pearls include:

·     Take a shower on arrival at destination.

·     Take a brief nap, if feeling exhausted.

·     Time-zone transitions < 8 hours east, promote a phase advance of the body clock.

·     Time-zone transitions < 8 hours west, promote a phase delay of the body clock

·     For journeys > 9 time zone hours east, it is more convenient to adjust by phase delay. 

·     The direction of adjustment may have implications for training and preparation for matches.

·     Most important determining factors are timely light exposure, physical exercise and melatonin administration. 

·     The rule is to modify behaviour rather than use medication to facilitate adjustment.

B. PROTECTING ATHLETE HEALTH

Protection of the health of the athlete starts before travel commences. Essential points to consider are listed in Table 3.

Important factors that need to be considered at the destination are different environmental conditions and culture, as well as the availability of medical facilities and services as explained in Table 4. 

Athletes are exposed to an increased risk of illness and injury during travel and participating at events. During the 2016 Olympic Games in Rio de Janeiro it was reported that overall, 8% of the athletes incurred at least one injury, and 5% an illness. This was slightly lower than in the Olympic Summer Games of 2008 and 2012⁴³. Accumulation of evidence shows the incidence and characteristics of sports injuries and illnesses that occur during sports events varies substantially between sports, perhaps demonstrating the need to tailor preventative measures to the specific context of each sport^3,43-52.

Furthermore para-athletes are a unique group with a wide variety of medical conditions, including intellectual or sensory (e.g. visual) or physical (e.g. amputation, spinal cord injury, cerebral palsy) impairments. They are often disabled, not only by their physical or intellectual impairments, but by a society that does not accommodate difference. Some common medical issues will prevail in relation to the impairment types that need to be considered as part of medical provisions at events. Over the course of time, epidemiological studies to monitor injury and illness in para-athletes have been initiated at both Paralympic Summer and Paralympic Winter Games^45,53.

In an article by Janse van Rensburg et al. describing epidemiology, risk markers and preventative strategies among para-athletes, the key points were⁶:

·     The para-athlete has a documented risk of contracting an illness at times of key sporting events.

·     Illness patterns are consistent for the Summer and Winter Paralympic Games.

·     Illness mainly affects respiratory, dermatological, and digestive systems.

·     Sporting code (specifically athletics) may be an important extrinsic risk marker for illness.

·     Age and sex are not accountable as risk markers.

Practical clinical guidelines to reduce the risk of illness in athletes

Illness prevention is a key component to protect the health of the athlete, and practi-cal approaches to prevent illness are essential to reduce the risk of illness that can restrain participation in important competitions. The prevention of illness in athletes involve implementation of behavioural, lifestyle and medical strategies in order to limit the transmission of infections. Nutritional strategies to maintain immunity in athletes, strategies to measure, monitor and manage training and competition load, and methods to detect early signs and symptoms of illness, over-reaching and overtraining are also important. General guidelines while competing or training abroad include advice to athletes, and measures that can be applied by medical staff and athlete support teams (Table 5)^3,5-6.

Although travelling abroad may be considered to equally affect both the individual athlete and the team-sport athlete in a similar way, there are several important elements of concern to consider (Table 6). 

CONCLUSION

The travelling athlete or team may suffer from travel fatigue and jet lag and may be exposed to a variety of insults e.g. allergens, pathogenic organisms and unfamiliar environmental conditions and cultures at the new destination. The extent thereof depends on intra- and inter-individual variation in the ability to tolerate circadian phase misalignment. Although many uncertainties exist on methods to advance or delay the circadian body clock, jet lag is potentially modifiable with strategic exposure to or avoidance of light, administration of melatonin and correct timing of exercise and meals. Furthermore, to ensure uncomplicated travel, environmental conditions need to receive attention and illness preventative measures need to be in place. The key to success remains in meticulous planning.

Dina C. Janse Van Rensburg, M.B.Ch.B., M.Sc., M.Med., M.D., F.A.C.S.M., F.F.I.M.S. 

Audrey Jansen van Rensburg, M.Sc.

Section Sports Medicine and SEMLI

Faculty of Health Sciences

University of Pretoria

Pretoria, South Africa

Martin P. Schwellnus, M.B.B.Ch., M.Sc.(Med.), M.D., F.A.C.S.M., F.F.I.M.S.

Section Sports Medicine and SEMLI

Faculty of Health Sciences

University of Pretoria

Pretoria, South Africa

International Olympic Committee (IOC) Research Centre

South Africa

Contact: christa.jansevanrensburg@up.ac.za

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