Teams competing internationally lose more to travel than the journey time suggests. The effects come from several independent sources that arrive together and resolve on different timescales.
The body clock realigns slowly
Circadian rhythms govern body temperature, hormone release and alertness, and they adjust to a new time zone at a limited rate of roughly one time zone per day.
Until realignment is complete, sleep occurs at biologically inappropriate times and peak physical capacity falls at hours that do not match the competition schedule.
Eastward travel is consistently harder than westward, because advancing the clock is more difficult than delaying it for most people.
Peak performance is tied to time of day
Physical output varies across the day, with strength and power typically higher in the late afternoon and lowest in the early morning.
An athlete whose internal clock is several hours behind may be competing at what their body treats as the middle of the night.
This is why teams manipulate light exposure, meal timing and training times before departure rather than waiting to adjust after arrival.
Immobility has its own consequences
Extended sitting reduces circulation in the legs, and fluid accumulates in the lower limbs over a long flight. Stiffness on arrival follows from that rather than from the time zone change.
Cabin air is very dry, and fluid losses through breathing accumulate over many hours in a way that is easy to under-replace.
Movement during the flight, compression garments and deliberate fluid intake address these directly, and they are separate from the circadian problem.
Routine disruption compounds the physiology
Meal timing, food availability, training facilities and sleeping environment all change simultaneously, and each is a variable that normally supports recovery.
Unfamiliar beds, noise and shared rooms reduce sleep quality independently of the time zone, which is why teams increasingly control accommodation specifications.
Digestion follows the body clock as well, so hunger arrives at hours that do not match the local meal schedule and intake falls in the first days after arrival, at exactly the point where recovery from the journey depends on it.
Recovery is planned into the schedule
Because realignment takes days, arrival timing is chosen against the competition date rather than for convenience, and early sessions are adjusted for the athletes' internal time.
The direction of the journey changes that calculation. A westward trip can allow competition soon after arrival, since the athlete's internal clock still treats the local evening as late afternoon, while the same distance eastward requires far more lead time.
Illness risk also rises around travel, and any athlete unwell before or after a journey needs assessment by the team's medical staff rather than a schedule adjustment alone.
