Travel and jet lag
Evidence: limited
Crossing several time zones desynchronises the body clock from local time, which hurts performance until the clock catches up, roughly one zone per day. Eastward travel is harder than westward. Timed light, timed melatonin and gradual pre-shifting speed the adjustment, and long-haul travel itself raises illness risk. The framework is sound; the size of any race-day gain from managing it is uncertain.
Why time-zone travel costs performance
The body runs on an internal clock, the circadian rhythm, that sets daily peaks and troughs in core temperature, alertness, reaction time and power output. Fly across several time zones and that clock is now out of step with local time. Until it resynchronises a runner is asked to perform at what their body still thinks is the middle of the night, with poorer sleep, alertness and physical output (Janse van Rensburg et al. 2021). This is jet lag, and it is distinct from travel fatigue, the simple tiredness of a long journey that resolves with a good night’s sleep.
The clock does not snap to the new zone. It shifts at roughly one time zone per day, so five zones takes about five days to fully adjust (Janse van Rensburg et al. 2021). For a race abroad this sets the planning horizon: arrive far enough ahead to adapt, or accept performing partly jet-lagged.
East is worse than west
Travelling east is harder than travelling west (Janse van Rensburg et al. 2021). Going east forces the body clock to advance, to fall asleep and wake earlier, and the human clock resists shortening its day far more than lengthening it. Going west the clock has to delay, which is closer to its natural drift and easier to do. A practical rule is that westward zones adjust faster, often nearer half a day each, while eastward zones take the full day or more (Janse van Rensburg et al. 2021). Plan extra adjustment time for eastward trips.
What actually helps
Three tools have the best support, and light is the strongest (Janse van Rensburg et al. 2021).
- Timed light exposure and avoidance. Light is the master signal that resets the clock. Travelling east, seek bright morning light and avoid evening light at the destination to pull the clock earlier; travelling west, do the reverse, seeking evening light (Janse van Rensburg et al. 2021). Getting the timing wrong can push the clock the wrong way, so the direction of travel dictates the schedule.
- Timed melatonin. Taken near the target bedtime at the destination, melatonin reduces jet lag when crossing five or more zones, and works best for eastward travel (Herxheimer & Petrie 2002). Doses from 0.5 to 5 mg work similarly, with higher doses simply more sedating (Herxheimer & Petrie 2002).
- Gradual pre-shifting. Moving sleep and wake times an hour or so per day towards the destination zone in the days before travel reduces the gap on arrival (Janse van Rensburg et al. 2021).
Adjusting meal times and exercise timing towards the destination clock, and protecting sleep on arrival, support the shift. Set your watch to destination time when you board to start thinking in the new zone.
Travel illness is the other cost
Jet lag is not the only problem with flying to a race. Athletes travelling across more than five time zones had two to three times the illness risk of those staying home or travelling shorter distances, mostly respiratory infections (Schwellnus et al. 2012). The causes stack: dry recirculated cabin air, close contact with infectious passengers, and the immune suppression that follows hard training and disrupted sleep (Schwellnus et al. 2012). Arriving rested but sick wastes the trip.
Planning a race trip
Arrive early enough to absorb most of the time difference, allowing about a day per zone and more for eastward travel. Start pre-shifting sleep a few days out, set your watch to destination time on boarding, and use destination-appropriate light and timed melatonin once there. On the plane, hydrate, move regularly and limit alcohol. Mind hygiene and contact in the cabin, since travel illness can cost more than the jet lag. Keep expectations modest: these measures shorten the disruption rather than removing it.