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Effect of airline travel on performance: A review of the literature


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The need for athletes to travel long distances has spurred investigation into the effect of air travel across multiple time zones on athletic performance. Rapid eastward or westward travel may negatively affect the body in many ways; therefore, strategies should be employed to minimise these effects which may hamper athletic performance. In this review, the fundamentals of circadian rhythm disruption are examined along with additional effects of airline travel including jet lag, sleep deprivation, travel at altitude and nutritional considerations that negatively affect performance. Evidence-based recommendations are provided at the end of the manuscript to minimise the effects of airline travel on performance.
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Effect of airline travel on performance: a review
of the literature
Whitney E Leatherwood, Jason L Dragoo
An additional supplementary
data is published online only.
To view this le please visit the
journal online (http://dx.doi.
org/ 10.1136/bjsports-2012-
Department of Orthopaedic
Surgery, Stanford University,
Stanford, California, USA
Correspondence to
Jason L Dragoo, Department of
Orthopaedic Surgery, Stanford
University, 450 Broadway
Street (Pavilion C, 4th Floor),
Redwood City, CA 94063-
6342, USA; jdragoo@stanford.
Accepted 18 September 2012
Published Online First
9 November 2012
To cite: Leatherwood WE,
Dragoo JL. Br J Sports Med
The need for athletes to travel long distances has
spurred investigation into the effect of air travel across
multiple time zones on athletic performance. Rapid
eastward or westward travel may negatively affect the
body in many ways; therefore, strategies should be
employed to minimise these effects which may hamper
athletic performance. In this review, the fundamentals of
circadian rhythm disruption are examined along with
additional effects of airline travel including jet lag, sleep
deprivation, travel at altitude and nutritional
considerations that negatively affect performance.
Evidence-based recommendations are provided at the
end of the manuscript to minimise the effects of airline
travel on performance.
Elite athletes are frequently required to travel long
distances for major competitions. Often, profes-
sional sport involves intermittent stints of long-haul
travel throughout an entire season; international
contests, such as the Olympic Games, World Cup
competitions and Grand Prix events, involve many
athletes coming together from different locations,
and hence various time zones.
Rapid airline travel across time zones has been
anecdotally noted to cause deterioration in athletic
performance. Inherent to travel are multiple vari-
ables, each potentially having their own effect on
athletic performance, yet it is difcult to determine
the extent to which each contributes to suboptimal
performance. Some factors associated with travel
that may affect performance include jet lag and cir-
cadian rhythm disruption, altitude, alterations in
diet and sleep deprivation.
Although there has been relatively little investiga-
tion into the topic, the available evidence suggests
that there is a detrimental effect of travel on ath-
letic performance due to jet lag and disruption of
circadian rhythmicity. Study of this topic is import-
ant in order to understand effects of travel on train-
ing and performance, which in turn might allow
effective timing and cueing strategies to optimise
performance at the destination.
This review will discuss principles of circadian
rhythms and jet lag and provide a review of the
current, relevant literature relating to travel and
performance. Finally, the review will offer some
evidence-based recommendations for athletes that
must undergo travel and perform optimally upon
The PubMed and Scopus databases were searched
between December 2011 and February 2012 using
the following terms: travel+performance,travel
+sports performance,circadian rhythm+perform-
ance,jet lag+performance,circadian rhythm
+sports performance,altitude+performance,
travel+nutrition+performance,sleep loss+per-
formanceand sleep deprivation+performance.
Articles were initially excluded if they were dupli-
cates and did not relate to aspects of travel and per-
formance measures. The preliminary search yielded
92 relevant articles in the PubMed database and 51
in the Scopus database (gure 1). With the excep-
tion of articles used for background information,
references were then considered relevant if they
met the following criteria: published in English,
presented or referenced an epidemiological study
or provided performance data and directly assessed
and/or referenced the effect of travel, factors asso-
ciated with travel or circadian rhythm disruption
on performance or surrogate measures of perform-
ance. The sources cited by these papers were then
reviewed using the above criteria and the process
was repeated. In total, 106 papers met criteria for
this review.
For the purposes of this review, long-distance
travel, unless otherwise dened, refers to ight
across three or more time zones.
Understanding circadian rhythm
The word circadianis derived from the Latin
circa diesmeaning about a day. Circadian
rhythms are daily biological rhythms that have
maximum or minimum function at certain times of
day and are synchronised to the 24 h lightdark
cycle. These biological rhythms are caused by oscil-
lators that appear to be located in most human cells
and are synchronised by a central oscillator, or
body clock, located in the suprachiasmatic nuclei
(SCN) of the hypothalamus. Each rhythm varies as
to the degree to which it is affected by environmen-
tal stimuli. Some rhythms such as core body tem-
perature, cortisol production and sleep/wake cycles
are rhythms that persist in a free-running state
without environmental cues.
Transmission of
time information from the central oscillator to the
peripheral oscillators is not completely understood
but occurs via neural and humoral stimulus.
Melatonin, inhibited by light and secreted by the
pineal gland during the hours of darkness,
thought to play an important role in transmission.
The SCN is in turn synchronised with the environ-
ment by the lightdark cycle, and to a lesser degree
by other environmental conditions such as social
routine, physical exercise and food uptake.
A circadian phase disruption results in desyn-
chronisation between the cellular oscillators in the
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SCN and the ones in the peripheral tissues. This desychronisa-
tion occurs because the central oscillators in the hypothalamus
adapt more quickly than the peripheral oscillators, which
become briey lost to hypothalamic control. The human body
performs optimally when the many biological rhythms that help
drive its functions are in synch.
Circadian rhythm of performance
It has been hypothesised that there is a circadian rhythmicity to
athletic performance.
While a few studies and reviews have
not supported this conclusion,
circadian rhythmicity or
time-of-day effects of various aspects of physical performance
have been studied and the data suggest that signicant effects
are evident in many areas. These include leg strength,
elbow exors,
jumping tasks,
sprint and anaer-
obic efforts,
and aerobic tasks.
21 22
Sport-specic tasks
such as soccer,
and swimming
have also been
shown to display rhythmicity. In a well-constructed experiment,
Kline et al attempted to detect a circadian rhythm in swim per-
formance as well as eliminate confounding variables such as
sleepwake cycle and environmental conditions in experienced
swimmers. Athletes were assessed for consecutive trials in a con-
trolled laboratory setting during which they were maintained on
a 3 h sleepwake cycle (1 h of sleep and 2 h of wakefulness in
dim light). Swim performances across all participants differed
signicantly by environmental time of day (gure 2).
Performance was signicantly worse at 02:00, 05:00 and
08:00 h than at 11:00, 14:00, 17:00, 20:00 and 23:00 h.
Additionally, in this study, performance was signicantly corre-
lated with body temperature rhythm and provides compelling
evidence for the possibility of an endogenous rhythm of athletic
Signicant circadian rhythmicity has also been
shown in surrogates of performance such as heart rate, blood
and blood lactate.
Establishing the existence of a daily oscillating rhythm of ath-
letic performance is important. If an endogenous rhythm of ath-
letic performance exists, one would expect (1) performance
after travel across multiple time zones to vary over a 24 h period
Figure 1 PRIMSA ow diagram.
Figure 2 Swim performance versus environmental time of day. Values
are double plotted to convey the cyclical nature of the rhythm. High z
scores indicate worse performance. Home team winning percentage
according to relative circadian advantage/disadvantage. Advantage
exists when home team is time zone adapted by 1, 2 or 3 days relative
to visiting team (1, 2, or 3 h advantage). Disadvantage exists when the
visiting team is time zone adapted by 1, 2 or 3 days relative to the
home team (1, 2, or 3 h disadvantage).
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displaying peak/trough performance windows,
(2) a deterior-
ation of the performance rhythm post-travel followed by a slow
rate of resynchronisation,
35 36
(3) generally, a more detrimental
effect of eastward travel as opposed to westward travel due to
difculties in adjustment after phase advance as compared with
phase delay and (4) specically, performance of an athletic task
several hours before or after the circadian peak windowwill
potentially be completed with less than optimal efciency.
Air travel and the performance circadian rhythm
In the study by Lemmer et al, 15 healthy, male elite athletes
were assessed for 24 h proles of several functions including
performance of a standardised training routine, body tempera-
ture, grip strength, blood pressure, heart rate, saliva melatonin
and cortisol after either westbound or eastbound travel. The
westbound athletes (n=13) ew from Frankfurt to Atlanta over
six time zones and the eastbound athletes (n=6) travelled over
eight time zones from Munich to Osaka. After travel, the rhyth-
mic patterns in body temperature and grip strength were greatly
disturbed on day 1 and jet lag symptoms, discussed below, per-
sisted 12 days longer for eastbound travellers.
Reilly et al showed deterioration of performance rhythms
after travel when 17 subjects (8 elite athletes and 9 support
staff) were studied to assess jet lag symptoms, performance vari-
ables and effect of temazepam on these variables after 9 h of
total ight from the UK to Florida.
The rate of adjustment of
body temperature and improvement of performance variables
was unaffected by the administration of temazepam; however,
jet lag symptoms and performance variables (leg, back, grip
strength, simple and choice reaction time) deteriorated to their
worst recorded values on the evening of the rst full day follow-
ing the ight. All of these variables were in phase with the circa-
dian rhythm of intra-aural temperature and gradually improved
such that performance of the measured variables had stabilised
between post-ight days 5 and 7. These data indicate a perturb-
ation in the circadian rhythm of these performance variables.
Understanding Jet lag
Jet lag is a circadian phase disruption that can occur when an
individual experiences an alteration to the external cues that
synchronise the body clock and drive biological circadian rhyth-
micity due to rapid air travel across multiple time zones. A dis-
ruption of this sort can also take place when an individual keeps
permanent night work schedules or participates in rotating shift-
Symptoms of jet lag include fatigue and general tired-
ness, sleep disruption, loss of concentration, loss of drive,
gastrointestinal distress, loss of appetite, headaches, general
malaise and various metabolic changes.
34 40 41
When perform-
ing tasks, jet lag may result in lapses in mental attention and
unusual errors in mental performance
such as distorted esti-
mation of time, space and distance.
Additionally, chronic
effects of circadian disruption and jet lag include depression,
exacerbation of de novo psychiatric disorders, increased risk of
developing cancer and infertility.
Symptoms of jet lag are
not experienced following longitudinal travel of any length
because it is the change in environmental conditions associated
with crossing time zones that is fundamental to the condition.
Effects of jet lag are evident with a 1 h time zone shift, but
shifts of 3 h or more are more often associated with symptoms.
Jet lag and performance
Previous studies and reviews have cited evidence that the com-
bined symptoms of jet lag have been shown to contribute to
deterioration of athletic performance.
Recently, in a
prospective study, Chapman et al
assessed post-travel jump
performance in 12 national team skeleton athletes (ve from
Australia and seven from Canada) and reported a signicant
variation in performance over the testing window. After initial
performance deterioration in some jumping tasks, the peak vel-
ocity, mean velocity and jump power eccentric utilisation ratios
(an indicator of power performance) for the travel group all sig-
nicantly increased 2 days after the long-haul ight. These data
show that airline travel may have a detrimental effect on jump
performance and neuromuscular control over the rst 12days
after travel.
Studies of team performance have illustrated a decline in per-
formance following travel across multiple time zones. Ten years
of Major League Baseball retrospective data were analysed to
determine the effect of travel on athletic performance.
study used the convention that for every time zone crossed,
resynchronisation requires one 24 h period.
As such, teams
were assigned a value indicating the cumulative time zones
crossed; wins and losses were then analysed based upon this
value. Teams were said to have an advantageif they crossed
fewer time zones than their opponents. Teams with a 3 h advan-
tage over other teams had a winning percentage of 60.6%,
which was more powerful than home-eld advantage.
Additionally, teams with a 3 h advantage won more games
than teams with 1 and 2 h advantages over their opponents
(gure 3). It appears that crossing more time zones correlates
with diminished performance.
Similarly, a retrospective analysis of archival data from six
seasons of Australian National Netball Competition show
support for a deterioration in the performance of teams after
travel across multiple time zones.
Travel was categorised as
local, northsouth, eastwest across one time zone, or across
two time zones. There was a signicant difference in points
scored at away matches between teams travelling northsouth
and teams crossing two time zones. The magnitude of perform-
ance loss was greatest for teams travelling across two time zones.
Additionally, the study found that crossing more time zones has
an additive effect on performance deterioration. When compar-
ing performance in the group crossing two time zones to those
not crossing any time zones, the effect size was greater than
Figure 3 Home team winning percentage according to relative
circadian advantage/disadvantage. Advantage exists when home team
is time zone adapted by 1, 2, or 3 days relative to visiting team (1-, 2-,
or 3-h advantage). Disadvantage exists when the visiting team is time
zone adapted by 1, 2, or 3 days relative to the home team (1-, 2-, or
3-h disadvantage).
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when comparing teams crossing two time zones to those cross-
ing a single time zone (gure 4). This provides support for the
hypothesis that travel across multiple time zones leads to
increased jet lag, and thus a greater decline in performance.
Data supporting a decline in performance following travel are
not always conrmatory. In a study by Bullock et al
perceived themselves as jet lagged to day 7, but there were no
signicant differences in sprint performance.
Direction of air travel and performance
Studies investigating the impact of the direction of travel on per-
formance have had differing results. Some data have shown that
eastward travel is more detrimental to performance. This is
because the body clocks rhythm is naturally longer than the
24 h lightdark cycle and is approximately 2526 h long;
as a
result, it is easier for the body to adapt to changes that lengthen
the day as opposed to shorten it. As such, exposure to light in
the early evening, for example, produces a delay in the body
clock and shifts the sleepwake cycle to a later hour; this is a
phase delay. On the other hand, a light stimulus during night
hours produces an advance in the body clock that shifts circa-
dian rhythm phases to an earlier hour; this is a phase advance.
This fact has implications for directionality of ight.
Many studies have shown that travellers ying eastbound tend
to experience more marked symptoms of jet lag that persist
longer, requiring lengthier time for resynchronisation, than
those of westbound travellers due to the bodys ability to more
rapidly adjust by phase delay.
In accordance with prior
studies, Lemmer et al found jet lag symptoms after westbound
ight were most pronounced through the rst three post-ight
days, while symptoms after eastbound ight were more severe
and persisted up to 7 days after arrival.
However, other studies have shown that westward travel can
be more detrimental than eastward travel. Diminished perform-
ance was most noticeable when teams competed in the evening
after travelling westward so that games were played close to the
visiting teamshome bed-time.
A separate hypothesis related
to circadian rhythm of performance asserts that, as performance
peaks in the evening, west coast teams should have an advantage
over teams from the east coast in late night games
because the
game would occur earlierby the visiting teams body time and
closer to the time of peak athletic performance.
Smith et al
studied 25 years of National Football League (NFL) data in
teams playing in Monday Night Football games with 2100 EST
start times. Data showed that west coast teams win more often
and by more points than east coast teams in such matches,
presumably because the west coast teams are playing closer to
their peak window.
Data from Winter et al showed Major
League Baseball teams travelling from west to east were more
likely to win than teams travelling from east to west. This phe-
nomenon was also noted in an analysis of retrospective data
from eight seasons of games in the National Basketball
Association when visiting teams performed better than home
teams after travelling west to east.
Jehue et al
found similar
evidence in a retrospective study analysing the effect of time
zone changes on NFL performance where, in night games, but
not day games, west coast teams displayed an advantage over
east coast teams.
Based on the above studies, the time of competition is a crit-
ical factor affecting performance post-travel. Athletes travelling
west to east for early afternoon competition may not perform
optimally since their home time is closer to morning hours.
Similarly, athletes travelling east to west may have a disadvantage
in late afternoon competition when their home time is closer to
bedtime. It may be advantageous to gradually shift the body
clock prior to competition when a disadvantageous travel sched-
ule is anticipated.
Disturbances in the sleepwake cycle following travel result in
periodic fatigue during the day, inability to sleep at night, sleep
fragmentation, premature awakenings, difculty in sleep initi-
ation and overall sleep loss.
Takahashi et al found total
sleep time was signicantly reduced on the second post-travel
day following long-haul ight and elevated activity during sleep
that persisted until the second post-travel day in 10 subjects
travelling to destinations with 811 h time differences.
loss is associated with sizeable effects on alertness,
62 63
disturbances in mood, cognition and motivation and may have
an affect on performance via these mechanisms.
Additionally, each individual uniquely experiences vulnerabilities
in their cognitive functioning as a result of sleep loss and may
be more susceptible to the effects of sleep deprivation when per-
forming one cognitive task over another.
67 68
Results are wide ranging in literature regarding the effect of
sleep loss on physical performance. Early reviews on the subject
have concluded there was little evidence to support consistent
69 70
Many studies test the effect of > 30 h of sleep
deprivation on performance
though it is unlikely that the
sleep loss experienced as a result of long-haul travel reects a
similar decit. Bambaeichi et al
assessed muscle strength of
knee extensors in eight women after one night of partial sleep
loss (2.5 h) and did not nd any signicant change in strength.
However, Reilly et al
studied eight male weight lifters
restricted to 3 h of sleep for three successive nights and found
deterioration in submaximal lift performance that was signi-
cant after the second night of sleep loss. In another study,
Waterhouse et al
found that a short nap improved sprint times
and measures of alertness, sleepiness and short-term memory in
10 healthy men restricted to 4 h of sleep the night before.
Therefore, employing strategies to shift circadian rhythms and
minimise the impact of sleep loss as a result of circadian disrup-
tion prior to competition may benet athletic performance.
Athletes travelling for competition do not often have the exi-
bility to schedule competitions during their peak performance
hours and instead must adapt to a predetermined schedule of
events. As a result, it may be benecial to shift circadian
Figure 4 Mean±SE for points difference (home marginaway
margin) for each pair of games for four groups of travel, including local
travel, northsouth travel, eastwest travel across one time zone and
eastwest travel across two time zones.
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rhythms so that the scheduled event falls during a peak per-
formance window. Studies have shown that the circadian phase
manipulation can be effective in shifting the body clock and that
it is easiest to try gradual shifts rather than to attempt a rapid
preadaptation and risk suffering jet lag prior to the trip.
49 77 78
Socioenvironmental limitations make adaptations more aggres-
sive than 12 h/day over 3 days unrealistic, and research has
shown no clear benet for adjustments of 2 h rather than 1 h/
Thus, shifting the body clock 1 h/day is recom-
52 62 77 79
. Preadaptation by means of a gradually
advancing sleep schedule has been achieved in controlled envir-
77 78
using timed light exposure, which suppresses
melatonin and facilitates wakefulness, and exogenous melatonin,
which enables sleep.
49 8083
The timing, intensity and wavelength of light provide important
cues for phase shifting the circadian rhythm.
One of the sim-
plest adaptation strategies involves timing light exposure to
delay or advance the body clock. To achieve phase delays, ath-
letes should seek light exposure in the early evening hours
(according to home time) and avoid exposure in the second half
of the night and early morning. If phase advances are desired,
begin light exposure in late evening to early morning (according
to home time).
49 62 78 84
Sunglasses may be helpful to avoid
inadvertent exposure to light.
49 62
Natural, outdoor light is
preferable to commercial light boxes if possible. The circadian
system is most affected by blue light and outdoor light contains
more blue light and is much more intense than commercial light
The American Academy of Sleep Medicine recommends the
appropriately timed use of melatonin supplements to promote
Studies show oral melatonin (in doses of 25 mg)
reduces subjective symptoms of jet lag and improves sleep in the
laboratory environment; however, the use of melatonin may be
counterproductive if taken at an inappropriate time of day.
49 52
In order to phase advance the circadian clock, melatonin should
be taken in the late afternoon or early evening, and in order to
phase delay, the supplement should be taken close to the sleep
period and in the morning.
77 78
The literature regarding the use of benzodiazepines for travel is
limited; however, it is anecdotally recognised as a treatment
method and regularly used by some athletes to help limit symp-
toms of jet lag when travelling for competition. Previous studies
in seasoned travellers and aircrews on transatlantic missions
have shown that treatment with benzodiazepines can improve
overall sleep quality, lengthen total sleep time, reduce time to
fall asleep and number of awakenings.
86 87
In two double-blind,
placebo-controlled trials of adaptation with triazolam to an 8 h
phase delay simulating westward travel, Buxton et al
that triazolam was signicantly more efcacious than placebo
treatment in all subjects, accelerating re-entrainment of circadian
rhythms markers and normalising parameters of sleep/wake
homeostasis such as sleep onset/awakening, and amount and dis-
tribution of rapid eye movement (REM), non-rapid eye move-
ment (NREM) and slow-wave sleep in six men. In order to
determine the effect of benzodiazepines on sport performance,
Golby and Hutson assessed performance following administra-
tion of temazepam (40 mg) compared with placebo in 12 volun-
teer professional soccer players who underwent reaction time
testing, soccer skills testing and critical icker fusion testing (a
reliable assessment of sedation and drowsiness). The authors
found no signicant difference in any measures between the
temazepam and control groups and no interaction effect, sug-
gesting that perceptual-motor performance is not impaired with
the use of temazepam.
More research is needed to determine
optimal dosing and effect of benzodiazepines on re-entrainment
of circadian rhythms, symptoms of jet lag and performance fol-
lowing travel, as well as its efcacy as compared to other chron-
obiotic supplements such as melatonin. However, the existing
data suggest that benzodiazepines may be helpful in treating
symptoms of jet leg without hindering sports performance.
Regulatory agencies have established safety guidelines that allow
airlines to pressurise cabins to a maximum altitude of 8000 ft
(2440 m). Average cabin pressures are 50006000 ft (1520
1828 m), which is equivalent to an inspired oxygen pressure
) of 132127 mm Hg. In a prospective study, the degree of
decline in oxygen saturation in athletes during long-haul ights
was investigated in 63 athletes and staff (45 athletes, 18 staff).
The study showed that oxygen saturation levels declined signi-
cantly after 3 and 7 h of ight (gure 5).
Modest falls in
oxygen saturation levels reect acute exposure to hypoxia at alti-
tude and are equivalent to those experienced by athletes upon
arrival at a similar altitude. It is plausible that time spent on
long-haul ights should be considered as time spent at
In general, studies have suggested that altitude exposure
results in a signicant decline in time trial performance in
aerobic sports.
These results are supported by Clark et al who
assessed 10 well-trained, male cyclists and triathletes not accli-
matised at altitude for peak oxygen consumption and mean
power output at simulated altitudes of 650, 3940 and 7220 ft
(200, 1200 and 2,200 m).
The study found a signicant dose
response effect of hypoxia on both peak oxygen consumption
(decrease of 7.2%/3280 ft or 1000 m of altitude) and mean
power output (decrease of 7.0%/3280 ft or 1000 m of altitude).
In another study, time to exhaustion decreased by 9.4%
between 985 ft (300 m) and 2620 ft (800 m) simulated altitude
and continued to decrease by 14.3%/3280 ft or 1000 m of
Figure 5 Mean oxygen saturation before ight, during ight and
upon arrival at destination. Measurements obtained by pulse oximetry
(error bars represent 95% CI of the mean).
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altitude subsequently.
Additionally, Gore et al
found a 67
76% decrease in peak oxygen consumption that was accounted
for by a decrease in O
delivery, indicating that reduced O
tension even at altitudes as low as 1900 ft (580 m) leads to
impairment of performance in a maximal effort lasting 5 min.
Faulhaber et al
reported signicant decreases in mean power
output during time trial performances in 11 healthy male ath-
letes from low (1970 ft or 600 m) to moderate (6470 ft or
1970 m) altitude. Interval sprint efforts, as well as interval
endurance trials, in eight elite female cyclists were signicantly
impaired during exposure to hypoxic conditions simulating a
moderate altitude of approximately 6890 ft (2100 m).
Given that biological responses to hypoxia begin during acute
exposures such as hypoxic conditions associated with air travel,
it would be benecial to understand the extent to which any
negative effects of hypoxia remain once travellers reach their
destination. Eight elite cyclists were studied at sea level and after
1, 7, 14 and 21 days of exposure to 7680 ft (2340 m) of alti-
tude. On day 1, max O
consumption and time to exhaustion
decreased by 12.8% and 25.8% respectively. Afterward, the
same measures increased dramatically from day 1 to day 14 sug-
gesting that endurance athletes competing at moderate altitudes
should expose themselves to similar altitude at least 14 days
before competition.
There are no published studies testing performance at sea
level following travel; however, it is plausible that athletes
would require a period of adaptation for optimised perform-
ance. For long ights (>10 h) it is be recommended that athletes
avoid arriving the same day of competition.
When athletes travel for competition, they introduce unfamiliar
stress to their normal body function at the time when maximal
and optimal performance is important. Nutrition is essential for
performance and the circadian desynchronisation that contri-
butes to feelings of jet lag also affects gastrointestinal function
and digestion.
97 98
Circadian disruption can cause a delay in the
absorption of food from the gastrointestinal tract after eating at
A large meal eaten late in the evening could lead to
bloating and sleep disruption,
making timing of meals import-
ant for re-entrainment of the digestion rhythm.
However, pat-
terns of activity and eating vary in different locations, causing
challenges when adapting to new mealtimes and rhythms of
activity. Travelling athletes may also have difculty nding access
to palatable foods that are typically included in their usual diet,
given a new environment. Thus, appropriate timing of meals
may be more important than the energy content of the
52 99
and small meals before and during ights are better
tolerated than large meals.
1 100
Studies have suggested that particular foods/diets are import-
ant for re-entrainment of the peripheral circadian clock. For
example, a meal high in carbohydrate, but low in protein may
facilitate uptake of tryptophan and its conversion to serotonin,
inducing drowsiness and sleep. On the other hand, a meal high
in protein but low in carbohydrate might enhance tyrosine
uptake and conversion to epinephrine, increasing arousal
Animal studies have shown that hypercaloric, high-fat
diets can impair adaptation to environmental signals after circa-
dian disruption
and circadian rhythms are readily adapted
when a restricted feeding diet is administered.
102 103
Gastrointestinal infections related to travelling are quite fre-
quent among athletes as hygiene standards for food and water
vary in foreign countries. Travellers diarrhoea is a common,
and usually self-limiting, condition; however, the associated
dehydration can be detrimental to athletes. As such, athletes
should avoid raw, or minimally cooked, foods and non-bottled
Analysing the effect of air travel on performance is problematic
for many reasons. First, the data strictly analysing an episode of
travel and subsequent results on performance are limited; there-
fore, it is difcult to glean an overall understanding of its
impact. Second, it is clear that many factors affect performance
in general, and distinguishing any aspect of travel as a cause for
deterioration of performance is challenging and met with a
variety of methodological issues. Thus far, attempts to remove
confounding factors have had limited success.
Third, much of
the literature is based on performance measures that are ques-
tionably related to athletic performance such as grip strength or
performance of one particular muscle group. It is unclear as to
whether these measures can serve as generalised benchmarks of
athletic performance. Fourth, the predominance of data avail-
able investigates the effect of jet lag or alterations in circadian
rhythms on athletic performance; however, the process of travel
encompasses many more variables. Studies isolating effects of
variables such as dehydration or alterations in diet following
travel are unavailable. Finally, there is signicant variation in
many of the available results that contribute to the base of
knowledge on this topic highlighting the difculties in studying
this issue. In many studies, sample size is small possibly due to
the logistics of organising air travel among a population of elite
athletes willing to participate in a scientic study.
Athletic performance is undoubtedly a composite of many
interacting variables. And, in testing the impact of travel on per-
formance, study designs are met with the challenging task of
eliminating a multitude of confounding variables associated
with individual performance. While it is relatively less difcult
to control environmental factors that may inuence circadian
rhythms such as light, activity or meals, it is decidedly more dif-
cult to control for elements that display a circadian rhythm all
their own such as sleepwake cycles.
Inability to eliminate this
variable, for example, blurs the ability to determine whether a
decline in performance is due to a shift in circadian rhythm, or
to sleep deprivation. Additionally, athletes exhibit differing rates
of resynchronisation following ight
which could contribute to
variability in results. It is also necessary to consider chronotype,
or an individuals propensity to prefer activity during certain
times of day, as this factor may inject inconsistency in results.
Additionally, mood and activity rhythms differ by several hours
between morning and evening types which will also have an
effect on circadian rhythm performance.
Motivation and
arousal level can affect performance as well, factors that vary
greatly among individuals. The extent to which one individual is
excited by competition cannot be controlled and will certainly
affect their desire to perform maximally during a given task.
Additionally, teams competing in their home environment enjoy
a home court/eld advantage and travelling teams are met with
a considerable task of overcoming such an advantage. This
advantage is often hard to separate from detriments in perform-
ance related to travel.
51 53 104
All of these factors taken together
highlight the difculty in generalising the results of current lit-
erature as some factors may play a more signicant role than
originally anticipated.
This topic can be more adequately investigated with studies
that utilise designs that better control for some of these con-
founding variables. Additionally, more research is needed to
analyse the effect of other aspects associated with travel and not
6 of 8 Leatherwood WE, et al.Br J Sports Med 2013;47:561567. doi:10.1136/bjsports-2012-091449
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just the effects caused by jet lag or alterations in circadian
1. In advance of travel, shift the body clock to the new time
zone through means of gradual, 1 h/day, shifts in sleep
52 62 77 79
2. Circadian phase shifting can be facilitated by proper timing
of light exposure
49 62 83
and the use of supplemental mela-
tonin, taken by mouth, in doses ranging from 2 to
5 mg.
49 78 8082 84
3. Exposure to natural daylight is preferred over exposure to
articial light.
4. Expose travellers to social contact at times appropriate for
local time at the destination.
5. Avoid caffeine during travel, as this stimulant can interfere
with appropriately timed restorative sleep and alter ability to
effectively adapt to a new time zone.
52 105
6. Short (2030 min) naps can be helpful in recovering from
sleep deprivation and restoring a normal state of arousal.
7. Consume extra uids for the duration of air travel to combat
dehydration. Avoid alcohol or caffeine, which act as diuretics
and can add to uid losses.
8. If possible, make arrangements for dietary selections that are
optimal for individual performance. While travelling, eat
smaller meals before and during ight; and, upon arrival,
time meals to match habits appropriate to the destination.
9. If travelling outside of the country, avoid non-bottled water,
raw or minimally cooked foods, and peel fruits and vegeta-
bles that have been washed.
Contributors JD and WL conceived the review, designed, undertook quality
assessment, checked quality assessment, performed part of writing or editing of the
review and made an intellectual contribution to the review; WL coordinated the
review and completed rst draft of the review and JD approved nal review prior to
submission and advised on the review.
Provenance and peer review Not commissioned; internally peer reviewed.
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Includes multiple factors associated with air travel that
potentially effect athletic performance, not simply jet lag.
Offers evidence-based recommendations that can be quickly
referenced to reduce the effect of air travel on athletic
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doi: 10.1136/bjsports-2012-091449
November 9, 2012
2013 47: 561-567 originally published onlineBr J Sports Med
Whitney E Leatherwood and Jason L Dragoo
review of the literature
Effect of airline travel on performance: a
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... 8,27,28 Further, recovery timelines for these athletes are complicated by consistent travel commitments and disrupted sleep patterns. 23,24,26 Estimates of overall lower extremity injury in professional basketball players suggest a pooled injury rate of 11.6 injuries per 1000 game-exposures (GEs) 9,37 ; however, recent estimates of ankle injury alone have not been evaluated. ...
... .020 Minutes per game c Total 21 (15)(16)(17)(18)(19)(20)(21)(22)(23)(24)(25)(26)(27)(28)(29) 13 (8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19) < .001 ...
... Regular games 22 (15)(16)(17)(18)(19)(20)(21)(22)(23)(24)(25)(26)(27)(28)(29) 14 (8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19) < .001 ...
Full-text available
Background Ankle injuries are more common in the National Basketball Association (NBA) compared with other professional sports. Purpose/Hypothesis The purpose of this study was to report the incidence and associated risk factors of ankle injuries in NBA athletes. It was hypothesized that factors associated with an increased physiologic burden, such as minutes per game (MPG), usage rate, and associated lower extremity injury, would be associated with increased ankle injury risk and time loss. Study Design Descriptive epidemiology study. Methods Ankle injury data from the 2015-2016 through 2020-2021 NBA seasons were evaluated. The truncated 2019-2020 season due to the COVID-19 pandemic was omitted. The primary outcome was the incidence of ankle injuries, reported per 1000 game-exposures (GEs). Secondary analysis was performed to identify risk factors for ankle injuries through bivariate analysis and multivariable logistic regression of player demographic characteristics, performance statistics, injury characteristics, and previous lower extremity injuries. Factors influencing the time loss after injury were assessed via a negative binomial regression analysis. Results A total of 554 ankle injuries (4.06 injuries per 1000 GEs) were sustained by NBA players over 5 NBA seasons, with sprain/strain the most common injury type (3.71 injuries per 1000 GEs). The majority of ankle injury events (55%) resulted in 2 to 10 game absences. The likelihood of sustaining an ankle injury was significantly associated with a greater number of games played ( P = .029) and previous injury to the hip, hamstring, or quadriceps ( P = .004). Increased length of absence due to ankle injury was associated with greater height ( P = .019), MPG ( P < .001), usage rate ( P = .025), points per game ( P = .011), and a prior history of foot ( P = .003), ankle ( P < .001), and knee injuries ( P < .001). Conclusion The incidence of ankle injuries was 4.06 per 1000 GEs in professional basketball players. Games played and prior history of hip, hamstring, or quadriceps injuries were found to be risk factors for ankle injuries. Factors associated with physiologic burden such as MPG and usage rate were associated with an increased time loss after injury.
... Flying between continents across multiple time zones can induce jet lag or circadian desynchronisation (changes in body clock rhythms), which can produce symptoms such as fatigue, sleep-wake disturbances, mood changes, bowel disturbance and impaired cognitive function [50]. There is evidence of the importance of circadian rhythmicity for athletic performance, with delineating effects for various aspects such as strength, anaerobic and aerobic performance [51]. The desynchronisation of the circadian rhythm caused by rapid air travel across multiple time zones has the potential to affect athletic performance over a 24-h period [51]. ...
... There is evidence of the importance of circadian rhythmicity for athletic performance, with delineating effects for various aspects such as strength, anaerobic and aerobic performance [51]. The desynchronisation of the circadian rhythm caused by rapid air travel across multiple time zones has the potential to affect athletic performance over a 24-h period [51]. ...
Full-text available
Golf is predominantly a skill-based sport where technical aspects are regarded as a priority area for improving performance. At present, most of the existing literature has focused on improving a player’s physicality, endurance and technical attributes in an effort to enhance performance. While important, the role of nutrition in elite golf has received little attention to date. The energy demands of the sport can vary depending on the level of the individual (recreational–professional), with distances of up to 20 km being covered and the time spent on the course ranging approximately 4–8 h each day. Like other sports, a focus on pre-game, during and post-game nutrition, including hydration, is integral to ensuring that individuals are adequately fuelled, hydrated and optimally recovered. For the elite athletes who travel extensively to international tournaments, it is important to understand the additional impact of travel on the body and consider the role nutrition can play in preventing illness and ensuring minimal disruption to golf performance. Lastly, the role of dietary supplements to enhance the performance of golfers is also important to consider. This review aims to consolidate the findings of the existing research focusing on nutrition strategies for golf performance and identify areas for potential future research.
... Jet lag is defined as the collection of symptoms that are manifested through the body's adaptations which occur due to a shift into a new time zone 13) . One of the major non chrono-biological stress factors of airline travel is the prolonged exposure to significantly lower air pressure than the norms, which results in a lower blood oxygen saturation that is stressful on the body [14][15][16] . In our study, travel fatigue is defined as a complex summation of the psychological, physiological, and environmental factors that affect an individual during a trip, which, in the long term, can reduce the ability to recover properly and perform at an optimal level. ...
... Jet lag is described as a circadian phase disruption that occurs when an individual experiences an alteration of external signals and cues that synchronize the body clock, the chronobiological circadian rhythmicity 16) . Disruptions like this typically take place when an individual partakes in rapid air travel spanning multiple time zones, and often results in symptoms such as fatigue, sleep pattern abnormalities, loss of concentration, loss of mental drive, gastrointestinal distress, loss of appetite, headaches, and metabolic changes including increased mean arterial blood pressure, resting heart rate, and increased glucocorticoid counts 10,35,36) . ...
Full-text available
Purpose] Purpose of this study is to measure the changes in various physiological markers and performance criteria for women basketball players over the course of a travel heavy season. [Participants and Methods] Fifty one Division-II female basketball players and a control group of 54 females joined this study. Measurements began at the beginning of the competitive season and concluded with final measurements at the end of the competitive season. [Results] The female basketball players showed noticeable increases in resting salivary cortisol, visceral trunk fat, resting heart rate, and resting blood pressure. These athletes also showed diminishment in iso-kinetic force of leg muscles, particularly in knee flexion strength. Vertical jump measurements also indicated a slight diminishment. In contrast, the control group experienced none of the same changes. [Conclusion] Over the course of a grueling flight schedule in combination with a full-length basketball season, the female athletes in this study showed significant declinations in many indicators of overall health. It is concluded that resulting prolonged intermittent stress of a travel-heavy season can lead to significant changes in certain physiological markers with notable decreases in isokinetic force of leg muscle.
... Although the team has arranged the best local hotel on the road, unfamiliar sleeping environments such as noise, lighting, and bedding in hotel rooms can all lead to poorer sleep quality [27]. The poor sleep quality would extend the time for sufficient recovery between games for athletes of the away team [28] which can increase the disadvantage of the away team. In addition, the separation from families can also have a negative effect on the psychology of the away team players and this effect will increase with time. ...
... However, some studies outline certain benefits that "bubble" environment can produce. In particular, a study of McHill and Chinoy (2020) examined the effects of "bubble" conditions on performance during National Basketball Association (NBA) finals whereby athletes did not have to travel across different time zones and upset their circadian rhythm which can lead to sleep loss and fatigue, further negatively affecting athlete's health, performance, recovery, and mood (Leatherwood and Dragoo, 2013). ...
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Although sport as an activity has been practiced for much of modern history, sports sciences were not considered a discipline of academic tradition until the 20th century (Fernández and García, 2018). The purpose and function of sport sciences are to investigate questions about motor behavior and performance, which must be solved on a scientific basis. According to data from PubMed, scientific research on sport sciences has increased in the last 10 years. Specifically, it is possible to affirm that more scientific studies were published in the 2010–2020 decade than in the entire previous period (1945–2009) (Maneiro, 2021). This brings us closer to the idea that this area of knowledge is in full expansion and apogee, in which sports scientists have a fundamental role. Analyzing more specifically the different fields of study, it is possible to affirm that some fields have more robust growth, while in others their growth is more moderate. Specifically, areas such as rehabilitation, exercise, or biomechanics show very notable growth, while others such as sports injuries, motor behavior analysis, performance analysis, or strength training show less notable growth (González et al., 2018). This special Research Topic entitled “Advances in Sport Science: Latest Findings and New Scientific Proposals” began with a double objective: on the one hand, to offer a space where scientists can continue to delve into the most consolidated scientific disciplines; and on the other hand, to open a path where those areas that still need more research could have a place. As a result, the great impact it has had on the community is noteworthy, to the extent that 27 articles have been published by 130 authors, and with a total global impact of almost 61,000 visits from multiple different countries, which has increased and improved knowledge on the following topics: performance analysis in individual and team sports (15 articles), the impact of COVID-19 on performance (3 articles), executive functions and physical fitness at an early age (3 articles), physical activity in older people (1 article), and psychological profiles in performance athletes (6 articles).
... LH travel can result in travel fatigue and jet lag, both of which can potentially prevent optimal physical and mental performance. [1][2][3] Travel fatigue is caused by challenges of LH travel, such as stresses encountered on the journey, 4,5 sleep disruption before 6,7 and during the journey, 1,8,9 limited access to preferred food/fluid, 10 and the aircraft cabin environment. 4,5 Travel fatigue can be acutely experienced after any individual long journey, in any direction; or chronically because of repetitive travel within a season. ...
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Elite athletes and their support staff are often required to travel for international competitions all over the globe, however little is known about their experiences of long-haul (LH) travel and its perceived effects on performance. The aim of this study was to explore elite athletes’ and support staffs’ perception of symptoms experienced following LH travel and the self-management strategies they used to mitigate these symptoms. Elite athletes and support staff ( n = 88), who had embarked on an LH flight (> 8 hours) in the previous 2 years for training or competition, completed a survey examining their perceptions of LH travel, symptoms experienced following the flight(s) and strategies they implemented to minimise the symptoms. Associations between symptoms experienced and travel strategies used with participant and journey characteristics were examined by Chi-squared tests. LH travel was widely perceived by participants to be disruptive to physical (86.4%) and mental performance (72.7%) and to increase the risk of illness and injury (86.4%). The most common symptoms experienced were related to fatigue and disruption to sleep. All participants implemented strategies to help mitigate the negative consequences of LH travel. Moving and stretching regularly in-flight and simple strategies for aligning the body clock to destination time were most prevalent. The study findings will allow the translation of research to better inform future guidelines that address the unique needs and priorities of elite athletes and support staff as they embark on LH travel for training and competition with a view to optimising performance outcomes.
... Moreover, sleep deprivation increases the risk of road traffic accidents (Herman et al., 2014;Cai et al., 2021). Overall, sleep deprivation can be considered a public health problem concerning, for example, the worlds of sport and art with the stress induced by competition and shows, frequency and duration of displacements and jet lag; night workers with the chronobiological desynchronization likely to be induced; older people with increased risks of insomnia; people with obstructive sleep apnea syndrome, anxiety and depression, fibromyalgia, and many other pathologies etc., (e.g., Van Reeth and Mennuni, 2002;Waterhouse et al., 2004;Leatherwood and Dragoo, 2013;Umemura et al., 2018;Serrano-Checa et al., 2020). ...
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CITATION Paillard T (2023) Detrimental effects of sleep deprivation on the regulatory mechanisms of postural balance: a comprehensive review. This review addresses the effects of sleep deprivation on postural balance based on a comprehensive search of articles dealing with this relationship in the electronic databases PubMed, Google Scholar, and ScienceDirect. Evidence suggests that postural balance is sensitive to acute and chronic sleep deprivation for everyone, including young and healthy subjects. Pathologies, aging and the circadian pattern aggravate and/or accentuate the effects of sleep deprivation on postural balance. It turns out that the different systems of information taking, decision making, and motor execution of the postural balance function are negatively affected by sleep deprivation. For example, regarding the information taking system, the sensitivity of visual perception and visuo-spatial performance and the oculomotricity are disrupted and the vestibulo-ocular reflex and the sensory reweighting are altered. Regarding the decision making system, the different brain areas activated for the regulation of postural balance are less active after sleep deprivation and the executive function and perception of verticality are impaired. Regarding the motor execution system, the agonist-antagonist muscle coordination can be modified. However, the different detrimental effects induced for each system of the postural balance function are not yet fully known and deserve further exploration in order to better understand them.
... Interestingly, two studies that found a negative relationship between sRPE and physical qualities were conducted with tennis players on international tours [70,71]. Travel can influence performance and recovery through factors such as compromised sleep and nutrition [106,107]. Therefore, although speculative, altered ability to recover may have played a mediating role in the results observed. Practitioners should also be cautious in interpreting a negative relationship between training load and physical qualities as advocating for a decrease in load, as this may hamper long-term athletic development. ...
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Background With the increasing professionalisation of youth sports, training load monitoring is increasingly common in adolescent athletes. However, the research examining the relationship between training load and changes in physical qualities, injury, or illness in adolescent athletes is yet to be synthesised in a systematic review. Objective The aim of this review was to systematically examine the research assessing internal and external methods of monitoring training load and physical qualities, injury, or illness in adolescent athletes. Methods Systematic searches of SPORTDiscus, Web of Science, CINAHL and SCOPUS were undertaken from the earliest possible records to March 2022. Search terms included synonyms relevant to adolescents, athletes, physical qualities, injury, or illness. To be eligible for inclusion, articles were required to (1) be original research articles; (2) be published in a peer-reviewed journal; (3) include participants aged between 10 and 19 years and participating in competitive sport; (4) report a statistical relationship between a measure of internal and/or external load and physical qualities, injury or illness. Articles were screened and assessed for methodological quality. A best-evidence synthesis was conducted to identify trends in the relationships reported. Results The electronic search yielded 4125 articles. Following screening and a review of references, 59 articles were included. The most commonly reported load monitoring tools were session ratings of perceived exertion (n = 29) and training duration (n = 22). Results of the best-evidence synthesis identified moderate evidence of positive relationships between resistance training volume load and improvement in strength, and between throw count and injury. However, evidence for other relationships between training load and change in physical qualities, injury, or illness were limited or inconsistent. Conclusions Practitioners should consider monitoring resistance training volume load for strength training. Additionally, where appropriate, monitoring throw counts may be useful in identifying injury risk. However, given the lack of clear relationships between singular measures of training load with physical qualities, injury, or illness, researchers should consider multivariate methods of analysing training load, as well as factors that may mediate the load–response relationship, such as maturation.
... As previously showed, travelling may have a negative effect on athletes' performance [10], due to sleep disorders, nutritional and appetite changes, travel fatigue (i.e., hours spent seated and disruption in daily rhythm and routines). Considering these negative effects on athletes' cognitive and physical levels, specific treatments to surpass these effects are necessary [10,11]. Thus, looking past the athletes' country of origin, the characteristics and place of competitions can provide important information for athletes and coaches to better prepare and select the most appropriate race course in the world. ...
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Our purpose was to find the fastest race courses for elite Ironman ® 70.3 athletes, using machine learning (ML) algorithms. We collected the data of all professional triathletes competing between 2004 and 2020 in Ironman 70.3 races held worldwide. A sample of 16,611 professional athletes originating from 97 different countries and competing in 163 different races was thus obtained. Four different ML regression models were built, with gender, country of origin, and event location considered as independent variables to predict the final race time. For all the models, gender was the most important variable in predicting finish times. Attending to the single decision tree model, the fastest race times in the Ironman ® 70.3 World Championship of around ~4 h 03 min would be achieved by men
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The aim was to test the hypothesis that one night of sleep deprivation will impair pre-loaded 30 min endurance performance and alter the cardio-respiratory, thermoregulatory and perceptual responses to exercise. Eleven males completed two randomised trials separated by 7 days: once after normal sleep (496 (18) min: CON) and once following 30 h without sleep (SDEP). After 30 h participants performed a 30 min pre-load at 60% [VO(2 max) followed by a 30 min self-paced treadmill distance test. Speed, RPE, core temperature (T(re)), mean skin temperature (T(sk)), heart rate (HR) and respiratory parameters VO(2 max), VCO(2), VE, RER pre-load only) were measured. Less distance (P = 0.016, d = 0.23) was covered in the distance test after SDEP (6037 (759) 95%CI 5527 to 6547 m) compared with CON (6224 (818) 95%CI 5674 to 6773 m). SDEP did not significantly alter T(re) at rest or thermoregulatory responses during the pre-load including heat storage (0.8 degrees C) and T(sk). With the exception of raised VO(2) at 30 min on the pre-load, cardio-respiratory parameters, RPE and speed were not different between trials during the pre-load or distance test (distance test mean HR, CON 174 (12), SDEP 170 (13) beats min(-1): mean RPE, CON 14.8 (2.7), SDEP 14.9 (2.6)). In conclusion, one night of sleep deprivation decreased endurance performance with limited effect on pacing, cardio-respiratory or thermoregulatory function. Despite running less distance after sleep deprivation compared with control, participants' perception of effort was similar indicating that altered perception of effort may account for decreased endurance performance after a night without sleep.
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Elite athletes and their coaches are accustomed to international travel for purposes of training or sports competition. Recreational participants are similarly, if less frequently, exposed to travel stress. Transient negative effects that constitute travel fatigue are quickly overcome, whereas longer-lasting difficulties are associated with crossing multiple time-zones. Jet-lag is linked with desynchronization of circadian rhythms, and its impact depends on the duration and direction of flight, flight schedule, and individual differences. Athletes' performances are likely to be affected for some days until the body clock is readjusted in harmony with local time. Knowledge of the physiological characteristics of the body clock can be used to develop behavioural strategies that accelerate readjustment, in particular the timing of outdoor or bright light exposure, perhaps melatonin ingestion, meals, and exercise. Attempts to promote sleep by use of drugs that adjust the body clock, induce sleepiness or promote wakefulness are relevant but discouraged in travelling athletes. Support staff should develop appropriate education programmes for their athletes who can then make informed choices about their behaviour and minimize the transient effects of jet-lag on their well-being and performance.
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Prolonged subjection to unstable work or lighting schedules, particularly in rotating shift-workers, is associated with an increased risk of immune-related diseases, including several cancers. Consequences of chronic circadian disruption may also extend to the innate immune system to promote cancer growth, as NK cell function is modulated by circadian mechanisms and plays a key role in lysis of tumor cells. To determine if NK cell function is disrupted by a model of human shift-work and jet-lag, Fischer (344) rats were exposed to either a standard 12:12 light-dark cycle or a chronic shift-lag paradigm consisting of 10 repeated 6-h photic advances occurring every 2 d, followed by 5-7 d of constant darkness. This model resulted in considerable circadian disruption, as assessed by circadian running-wheel activity. NK cells were enriched from control and shifted animals, and gene, protein, and cytolytic activity assays were performed. Chronic shift-lag altered the circadian expression of clock genes, Per2 and Bmal1, and cytolytic factors, perforin and granzyme B, as well as the cytokine, IFN-γ. These alterations were correlated with suppressed circadian expression of NK cytolytic activity. Further, chronic shift-lag attenuated NK cell cytolytic activity under stimulated in vivo conditions, and promoted lung tumor growth following i.v. injection of MADB106 tumor cells. Together, these findings suggest chronic circadian disruption promotes tumor growth by altering the circadian rhythms of NK cell function.
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Jet lag has potentially serious deleterious effects on performance in athletes following transmeridian travel, where time zones are crossed eastwards or westwards; as such, travel causes specific effects related to desynchronization of the athlete's internal body clock or circadian clock. Athletes are particularly sensitive to the effects of jet lag, as many intrinsic aspects of sporting performance show a circadian rhythm, and optimum competitive results require all aspects of the athlete's mind and body to be working in tandem at their peak efficiency. International competition often requires transmeridian travel, and competition timings cannot be adjusted to suit individual athletes. It is therefore in the interest of the individual athlete and team to understand the effects of jet lag and the potential adaptation strategies that can be adopted. In this review, we describe the underlying genetic and physiological mechanisms controlling the circadian clock and its inherent ability to adapt to external conditions on a daily basis. We then examine the fundamentals of the various adaptation stimuli, such as light, chronobiotics (e.g. melatonin), exercise, and diet and meal timing, with particular emphasis on their suitability as strategies for competing athletes on the international circuit. These stimuli can be artificially manipulated to produce phase shifts in the circadian rhythm to promote adaptation in the optimum direction, but care must be taken to apply them at the correct time and dose, as the effects produced on the circadian rhythm follow a phase-response curve, with pronounced shifts in direction at different times. Light is the strongest realigning stimulus and careful timing of light exposure and avoidance can promote adjustment. Chronobiotics such as melatonin can also be used to realign the circadian clock but, as well as timing and dosage issues, there are also concerns as to its legal status in different countries and with the World Anti-Doping Agency. Experimental data concerning the effects of food intake and exercise timing on jet lag is limited to date in humans, and more research is required before firm guidelines can be stated. All these stimuli can also be used in pre-flight adaptation strategies to promote adjustment in the required direction, and implementation of these is described. In addition, the effects of individual variability at the behavioural and genetic levels are also discussed, along with the current limitations in assessment of these factors, and we then put forward three case studies, as examples of practical applications of these strategies, focusing on adaptations to travel involving competition in the Rugby Sevens World Cup and the 2016 Summer Olympics in Rio de Janeiro, Brazil. Finally, we provide a list of practice points for optimal adaptation of athletes to jet lag.
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Individual differences in vulnerability to neurobehavioral performance impairment during sleep deprivation are considerable and represent a neurobiological trait. Genetic polymorphisms reported to be predictors have suggested the involvement of the homeostatic and circadian processes of sleep regulation in determining this trait. We applied mathematical and statistical modeling of these two processes to psychomotor vigilance performance and sleep physiological data from a laboratory study of repeated exposure to 36 h of total sleep deprivation in 9 healthy young adults. This served to quantify the respective contributions of individual differences in the two processes to the magnitudes of participants' individual vulnerabilities to sleep deprivation. For the homeostatic process, the standard deviation for individual differences was found to be about 60% as expressed relative to its group-average contribution to neurobehavioral performance impairment. The same was found for the circadian process. Across the span of the total sleep deprivation period, the group-average effect of the homeostatic process was twice as big as that of the circadian process. In absolute terms, therefore, the impact of the individual differences in the homeostatic process was twice as large as the impact of the individual differences in the circadian process in this study. These modeling results indicated that individualized applications of mathematical models predicting performance on the basis of a homeostatic and a circadian process should account for individual differences in both processes.
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Home advantage is a well-established phenomenon in many sports. The present study is unique in that it includes different sports analysed in the same country, at the same level of competition, and over the same time period. Nine team sports from Spain were included: baseball, basketball, handball, indoor soccer, roller hockey, rugby, soccer, volleyball, and water polo. Data for five seasons (2005-2006 to 2009-2010) were obtained, totaling 9,472 games. The results confirmed the existence of home advantage in all nine sports. There was a statistically significant difference between the sports; home advantage was highest in rugby (67.0%), and lowest in volleyball (55.7%), water polo (56.2%), and roller hockey (58.3%). The design of the study controlled for some of the likely causes of home advantage, and the results suggested that the high home advantage for rugby was likely a reflection of the continuous, aggressive, and intense nature of the sport.
The 2000 Sydney Olympic Games will be a highlight of the sporting careers of many Australian athletes. Importantly it will also provide the athletes with the unique opportunity to perform without having to be concerned about jet lag affecting their performance.
The expanding science of circadian rhythm biology and a growing literature in human clinical research on circadian rhythm sleep disorders (CRSDs) prompted the American Academy of Sleep Medicine (AASM) to convene a task force of experts to write a review of this important topic. Due to the extensive nature of the disorders covered, the review was written in two sections. The first review paper, in addition to providing a general introduction to circadian biology, addresses "exogenous" circadian rhythm sleep disorders, including shift work disorder (SWD) and jet lag disorder (JLD). The second review paper addresses the "endogenous" circadian rhythm sleep disorders, including advanced sleep phase disorder (ASPD), delayed sleep phase disorder (DSPD), irregular sleep-wake rhythm (ISWR), and the non-24-hour sleep-wake syndrome (nonentrained type) or free-running disorder (FRD). These practice parameters were developed by the Standards of Practice Committee and reviewed and approved by the Board of Directors of the AASM to present recommendations for the assessment and treatment of CRSDs based on the two accompanying comprehensive reviews. The main diagnostic tools considered include sleep logs, actigraphy, the Morningness-Eveningness Questionnaire (MEQ), circadian phase markers, and polysomnography. Use of a sleep log or diary is indicated in the assessment of patients with a suspected circadian rhythm sleep disorder (Guideline). Actigraphy is indicated to assist in evaluation of patients suspected of circadian rhythm disorders (strength of recommendation varies from "Option" to "Guideline," depending on the suspected CRSD). Polysomnography is not routinely indicated for the diagnosis of CRSDs, but may be indicated to rule out another primary sleep disorder (Standard). There is insufficient evidence to justify the use of MEQ for the routine clinical evaluation of CRSDs (Option). Circadian phase markers are useful to determine circadian phase and confirm the diagnosis of FRD in sighted and unsighted patients but there is insufficient evidence to recommend their routine use in the diagnosis of SWD, JLD, ASPD, DSPD, or ISWR (Option). Additionally, actigraphy is useful as an outcome measure in evaluating the response to treatment for CRSDs 1 Guideline). A range of therapeutic interventions were considered including planned sleep schedules, timed light exposure, timed melatonin doses, hypnotics, stimulants, and alerting agents. Planned or prescribed sleep schedules are indicated in SWD (Standard) and in JLD, DSPD, ASPD, ISWR (excluding elderly-demented/nursing home residents), and FRD (Option). Specifically dosed and timed light exposure is indicated for each of the circadian disorders with variable success (Option). Timed melatonin administration is indicated for JLD (Standard); SWD, DSPD, and FRD) in unsighted persons (Guideline); and for ASPD, FRD in sighted individuals, and for ISWR in children with moderate to severe psychomotor retardation (Option). Hypnotic medications may be indicated to promote or improve daytime sleep among night shift workers (Guideline) and to treat jet lag-induced insomnia (Option). Stimulants may be indicated to improve alertness in JLD and SWD (Option) but may have risks that must be weighed prior to use. Modafinil may be indicated to improve alertness during the night shift for patients with SWD (Guideline).
The rhythms of life are ever pervasive, touching almost every aspect of our lives. We are finely tuned to the cycle of light and dark, so that we normally sleep during the night and are active during the day. Physiological rhythms are, however, not just slaves to the solar day, but are actually generated endogenously within the suprachiasmatic nuclei in the hypothalamus and are entrained via the retina. The circadian timing system is organized hierarchically with the suprachiasmatic nuclei providing neural and/or hormonal cues to the various organ systems, allowing them to express their own rhythmic physiological output. There is now a substantial body of evidence emerging that disruption of rhythmicity through altered sleep/wake patterns and exposure to light, or through endogenous disruption of key determinants of endogenous rhythms, can be detrimental to health. Circadian rhythm disturbances have long been associated with mood disorders, especially delayed sleep onset, and evidence is accumulating that alterations to the cellular timing system may underpin some aspects of the disorders. For example, mice carrying mutations in either Clock or per2 spend less time immobile in swim tests, which has been suggested as mimicking mania. In humans, single nucleotide polymorphisms in Clock and other clock genes have been associated with depression. With this increasing knowledge we may predict that new antidepressant drugs will emerge that, as a primary or secondary mechanism of action, target and correct abnormalities in the circadian timing system.
Athletes train and compete at different times of the day according to personal preferences, schedule of team training or timing of competition. Many human performance variables follow the circadian rhythm in physiological measures, in phase with the rhythm in core body temperature. This correspondence applies to components of performance, physiological determinants of performance with high power output, psychophysical loading and competitive time trials. There is evidence that circadian rhythms in exercise performance are, in part, endogenously driven. Human performance rhythms are disrupted when athletes travel rapidly across multiple meridians, or are engaged in nocturnal shift-work. Few sports participants maintain high-performance standards when operating shift-work regimens. In contrast, travelling across time-zones is a contemporary feature of competitive sport for sojourns and training camps and participating in international contests. Athletes like all travellers experience jet lag symptoms when crossing multiple time-zones. Symptoms are worse and last longer following flights to the east compared to flying westwards. Performance rhythms re-adjust to the new local time at about the same time as that of core temperature. Experience with Olympic athletes travelling between Europe and Australia is that adjustment may be by phase advance or phase delay depending on timing of departure and disembarkation, time of arrival and exposure or avoidance of natural light, and activity in the early days in the new time-zone. Adjustment can be assisted by means of a behavioural strategy that combines the body clock and the homeostatic drive to sleep. Exclusion of long naps, the diurnal timing of physical training and social events form part of this strategy, as do eating and drinking behaviour. Exercise is a potential resynchronising agent when utilised at the correct time of day. Pharmacological treatments, including use of melatonin, have found favour in some contexts but their phase response curves pose difficulties for their administration in athletes travelling on long-haul flights. In view of the national governing bodies' stances on use of pharmacological agents and supplements by athletes, the behavioural strategy to cope with jet lag has been advocated.