Jet lag isn't just feeling tired—it's a temporary circadian misalignment affecting hormones, temperature, digestion, and athletic performance that runners feel particularly strongly.

• Endurance performance depends on precise timing of biological functions that get disrupted during travel
• Core body temperature minimum sits 2-3 hours before wake time and is key to understanding light exposure timing
• Morning light moves your clock earlier, evening light moves it later
• Delay path (treating destination as behind rather than ahead) is usually faster and kinder for adjustment
• Time-shifting apps like TimeShifter and FlyKitt provide personalized schedules for light, darkness, and supplements
• Caffeine timing can help shift your clock but should be used strategically
• Keep naps short (20-30 minutes) to avoid disrupting nighttime sleep
• Place easy aerobic workouts during times you need to stay alert
• Save harder workouts for when your body temperature is higher, not near your temp minimum
• Older adults can still shift their clocks but it takes longer
• PR races are generally more successful when sleeping in your own bed without travel disruption

If you're traveling for races this season, stack your controllables by managing light exposure, darkness, and caffeine timing. Remember your body will adapt—you've done harder things and can still have a fantastic race experience!

Resources: 
NASA Technical Reports Server
Semantic Scholar PDFs 
PMC
Oxford Academic 
PMC
JCI Insight
Journal of Circadian Rhythms 
PMC
Cochrane
PMC 
PubMed
PMC
thenbsca.com 
Timeshifter®+1
Fount

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