In my previous article on sleep deprivation, I explored its general effects on exercise capacity, especially in situations of extreme exercise such as adventure racing and sustained military operations.
From an athletic perspective, the greatest impact of transmeridian (across time zones) travel is the physiological and psychological disruptions on training or competition. In addition to insomnia and sleep-related issues, jet lag can induce feelings of disorientation, fatigue, irritability, light-headedness, impatience, lack of energy, and problems with appetite and bowel movements.
Individual variability exists in tolerance, but a threshold of three or more time zones appear to be required for significant symptoms in most individuals. Re-synchronization of circadian rhythms lags at about 1 day per time zone travelled, with the problems from jet lag typically most prominent during the first 3-4 days upon arrival. Arousal from social contact may mask many symptoms but does not completely compensate or readjust circadian rhythms.
Travelling to unfamiliar environments and disruptions in circadian rhythm can be a major stressor and impediment for athletes. However, proper planning can help to minimize though not necessarily eliminate the impairment on exercise performance. The following approaches may be useful for both athletes and shift workers in assisting with adaptation.
The use of stimulants to artificially and transiently elevate alertness and arousal, along with enhancing concentration, has been a common means of mitigating sleep deprivation and fatigue. Caffeine is possibly the most common legal stimulant in both natural (coffee, chocolate) and pill forms. Caffeine has historically been banned by most sport governing bodies and the International Olympic Committee, but has been de-listed, partly due to its overwhelming societal prevalence. That it has benefits on improved alertness is indisputable, with controlled studies demonstrating sustained vigilance and marksmanship in soldiers with sleep deprivation when provided caffeine (5).
During my doctoral studies, I was a participant for a number of studies on the ergogenic effects of caffeine and other stimulants during strenuous exercise, and it was readily evident the strength of such stimulants. The operational context for these studies were usage by soldiers and special forces personnel on sustained missions, but such studies had the added function of contributing to the regulation of ergogenic aids by sporting agencies. In a series of studies, caffeine and ephedrine (a stimulant), alone or in combination, greatly increased high-intensity exercise duration to exhaustion compared to placebo, with caffeine effects remaining into the afternoon even with morning supplementation. However, habituation to caffeine is evident, with the magnitude and duration of effects greater in nonusers than in users (1). Therefore, if used for performance benefits, athletes should abstain or minimize regular caffeine usage.
Another stimulant I was tested with was the psychostimulant modafinil, marketed under the trade names Alertec and Provigil. Used for treating narcolepsy, it gained a high profile through the discovery of its illegal use by track and field athletes in the mid-2000s. In studies at my doctoral laboratory, ingestion of modafinil significantly increased tolerance time at 85% VO2max, with ratings of perceived exertion decreasing dramatically and a likely contributor to the improvement (3). Personally, I certainly remember the relative ease of the hard exercise in one trial, even though I was blinded to conditions. I also remember going for a hard 120 km group ride that same afternoon and being uncharacteristically strong and putting the hurt on my friends!
It must be emphasized that modafinil is banned by WADA, and I’m only including it here for educational purposes!
The contrasting pharmacological approach to optimizing alertness and resistance to fatigue is substances that may enhance the ability of individuals to attain adequate quantity and/or quality of sleep. The use of sleeping pills (benzodiazepines) and other sedatives to induce the onset of sleep may appear to be beneficial with travel. However, while they may promote sleep, the quality and ergogenic effect of such sleep is questionable, with little evidence of advantageous effects on chronobiology and shifting circadian rhythms (4). The potential for addiction to sedatives such as alcohol and barbiturates also forms a strong counterindication for their use in sleep enhancement except for clinical conditions.
Melatonin is a natural hormone that is a precursor to a decrease in alertness and appears to prepare the body for sleep. Therefore, the use of exogenous melatonin may potentially be beneficial for athletes and shift workers in aiding to reset the circadian rhythm to a new sleep/wake cycle, though research on optimal dosing and clear evidence of efficacy in all users are unclear.
Melatonin is categorized as a herb or supplement rather than a pharmaceutical by the US Food and Drug Administration, and therefore is available without a prescription but also without strict regulation of purity. An additional caveat with melatonin is that the timing of its ingestion appears to be critical in its ultimate effect. Ingestion after the trough in circadian body temperature (i.e. in early morning with a normal sleep/wake cycle) appears to phase-delay circadian rhythm. In contrast, a phase-advance occurs when melatonin is taken prior to the peak in body temperature (i.e. about 8 h following wakeup). Furthermore, ingestion during the normal sleep cycle (i.e. from bedtime through to wakeup) will aid in inducing drowsiness but does not appear to have any chronobiotic effect.
Overall, the ergogenic effect of melatonin for jetlag recovery is equivocal and may be minimal, especially in individuals with busy schedules upon arrival. This was evidenced by the lack of any significant benefit from melatonin ingestion in British athletes travelling to Australia across ten time zones, with no demonstration of improvement in any symptoms of jetlag compared to a placebo group (2).
Travel to a major competition can be the most enjoyable part of being an athlete, both in the competition itself and also the thrill from shaking up your normal routine. If the travel is extreme, disruption in performance can occur for days to weeks, but the importance of quality sleep remains paramount. The supplements listed here may aid in the adaptation process. But as with all training tools, it is best to first try them out of competition, as may occur during business travel and trying to stay awake at meetings!
1. Bell DG and McLellan TM. Effect of repeated caffeine ingestion on repeated exhaustive exercise endurance. 35: 1348-54, 2003.
2. Edwards BJ, Atkinson G, Waterhouse J, Reilly T, Godfrey R and Budgett R. Use of melatonin in recovery from jet-lag following an eastward flight across 10 time-zones. Ergonomics 43: 1501-1513, 2000.
3. Jacobs I and Bell DG. Effects of acute modafinil ingestion on exercise time to exhaustion. Med.Sci.Sports Exerc. 36: 1078-1082, 2004.
4. Lemmer B. The sleep-wake cycle and sleeping pills. Physiol.Behav. 90: 285-293, 2007.
5. McLellan TM, Kamimori GH, Bell DG, Smith IF, Johnson D and Belenky G. Caffeine maintains vigilance and marksmanship in simulated urban operations with sleep deprivation. 76: 39-45, 2005.
Stephen Cheung is a Canada Research Chair at Brock University, with a research specialization in the effects of thermal stress on human physiology and performance. He can be reached for comments at email@example.com .