On arrival, depending on the timing, intensity, and duration, exposure to bright light (especially natural light) can advance or delay the circadian phase (30). Because melatonin secretion is inhibited on exposure to bright light and increased during darkness, allowing or restricting light exposure would seem an ideal prerequisite for altering melatonin secretion to suit circadian phase delay or advance. It has been demonstrated that fluorescent and blue light can also be used to effectively suppress melatonin, as they simulate the photic environmental stimuli associated with daytime light (14). For example, Wright, Lack, and Partridge (53) found that different light-emitting diodes were effective in suppressing melatonin, with the blue/green diode being more effective than any others. Desan et al. (15) found that the Litebook light-emitting diode light therapy (which uses shortwave blue light) was an effective device for treatment of seasonal affective disorder, which could also be repurposed for extending melatonin suppression. Recently, intermittent transcranial light has also been researched, where exposure to bright light through the ear canal (4 × 12 minutes per day) has been shown to have a positive effect on overall subjective jet lag symptoms after cumulative days of treatment (23), but no effect on circadian phase shifts after acute and short-term treatment of 1 × 12 minutes exposure (10). The exact physiological mechanisms are currently not understood, although transcranial bright light has been shown to have no effect on melatonin secretion, yet a positive effect on brain (32,43) and psychomotor function (47). Some practical guidelines from the literature on managing light exposure are provided in behavioral management plan (Figures 1 and 2).
Although traveling poses several nutritional challenges, many of these can be overcome before travel. Food requirements should be discussed with those who will provide catering at the new destination and during transit. If requirements are unable to be met, then staff and athletes may need to travel with additional supplementation. During travel, the dry air circulated in-flight cabins can increase the likelihood of dehydration; therefore, special attention should be paid to athletes' fluid intake (36,50). On arrival, if trying to adjust the circadian rhythm to the destination's time zone, meal times should coincide with that of the destination to aid circadian phase advances or delays (36). To minimize the risk of gastrointestinal illness, athletes should seek to avoid drinking local water (including ice cubes and water for brushing teeth) and the consumption of raw foods or those that may have been washed in contaminated water. In addition, the adoption of good personal hygiene practices (i.e., frequent hand-washing, hand-sterilizers etc.) will also help to minimize the risk of illness and diarrhea. Traveling athletes are often directed to avoid the intake of caffeinated beverages because of concerns regarding the potential diuretic effects of caffeine. However, although the general consensus of evidence suggests that moderate amounts of caffeine have minimal impact on overall hydration status (1), athletes should nonetheless avoid the consumption of caffeinated beverages because of the purported impact on wakefulness and interference with the adjustment of circadian rhythms. Burke et al. (11) recently demonstrated that caffeine ingestion caused ∼3 hours delay in the circadian melatonin rhythm, which could potentially induce poorer sleep quality and greater lethargy. Similarly, there is evidence that alcohol intake can also disturb normal sleep patterns (19) and should subsequently be avoided.
Timed exercise, appropriate clothing, and seating arrangements are hypothesized to reduce fatigue in a traveling athlete (30,35). When possible, periods of mobilization should be practiced to promote blood flow and reduce the risk of venous thromboembolism, joint stiffness, and muscle cramps that could result from long periods of inactivity during travel (5,30,41). Unfortunately, long haul flights do not provide the luxury of a 30-minute service stop. Thus, all activation and walking must be performed on the plane. In-flight activities such as simple stretching and mild isometric exercises while seated or walking in the cabin when it is safe to do so are recommended to reduce muscle stiffness, the risk for thrombosis, and other discomforts associated with prolonged sitting (30). After arriving at the final destination, to benefit from exercise-induced circadian phase shifts, it is recommended to perform exercise early in the morning when body temperature is lowest to promote phase delays and in the evening to gain phase advances (30). However, some studies have reported that exercise might not reliably shift circadian rhythms, but could be beneficial for maintaining arousal levels after travel (25). Some guidelines on exercise and training a traveling athlete are compiled from the literature and produced in Figures 1 and 2.
Compression garments have also been suggested to provide beneficial effects in alleviating discomfort and difficulties associated with prolonged sitting in a cramped position during travel (35). Belcaro et al. (5) and Scurr et al. (41) propose that compression stockings when worn below the knee can significantly reduce the risk of blood pooling and venous thromboembolism. Recently, nerve stimulation has also been studied where electrical stimulation of the peroneal nerve has been shown to increase blood flow to the lower leg (46), enhance venous return by up to 95% (26), and be more effective than both water-aerobic exercise and passive rest at reducing muscle pain in young soccer players (44). Furthermore, Beaven et al. (4) reported enhanced self-assessed energy levels and enthusiasm when electrostimulation was combined with compression garments, and an accelerated return of creatine kinase to baseline levels after rugby competition when compared with compression garments alone. Subsequently, it may be logical to assume that the use of electrical stimulation during travel would have both a physiological benefit as well as a psychological benefit. However, little research exists in relation to the use of electrical stimulation on physiological performance after travel or periods of prolonged sitting.
Jet lag effects are influenced by a number of individual differences in people, and these range from chronotype, age, fitness levels, and adaptability of sleeping patterns (34). Chronotype refers to the behavioral manifestation of an individual's underlying circadian rhythms. A person's chronotype is the propensity for the individual to sleep at a particular time during a 24-hour period. Morning-type people who retire early and arise early are less affected flying eastward, whereas evening type people who retire late and wake up late have less difficulty flying westward (25). The influence of age on travel-related circadian rhythm disruptions should also be considered while planning coping methods. Although older (50 + years) individuals may be less affected by jet lag symptoms, sleep and alertness levels of middle-aged travelers (37–52 years) are greatly affected after travel, compared with 18- to 25-year-olds (25). Physically fitter individuals should experience less difficulty with jet lag as they adapt to travel and sleep disruption (51). Adaptability of sleeping patterns relates to an individual's ability to adjust their times of sleeping, and are influenced less by the conditions in which they sleep. It is proposed that these factors would lessen the impact of jet lag on an individual who undertakes long haul travel (48). Further experimental support is required to verify these predictions and the impact these factors have on individuals and their response to prolonged travel. However, although these differences are smaller in an athletic population (34), knowing this information on individual sleeping habits and circadian rhythms would assist in planning appropriate interventions.
A traveling athlete creates unique challenges for strength and conditioning coaches in accomplishing effective total athlete management. However, awareness of the fundamental mechanisms of fatigue associated with travel and implementing recommended coping measures can provide some favorable outcomes. Available literature in this area suggests that a greater focus on strategic timings for sleep/nap, light exposure/avoidance, and food/fluid intake can help alleviate the adverse effects of travel on physiological factors and athletic performance. Studies also propose that planned pretravel adaptation measures, use of compression garments, timed exercise, practice of good personal hygiene, and proper management of travel logistics (to avoid psychological stress and/or to gain from favorable departure and arrival timings) can be beneficial. In addition, further coping methods available to explore include nerve stimulation and transcranial light exposure, both of which require further research. Finally, understanding and considering an athlete's age and chronotype related differences can make the coping strategies more effective.
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