Having flown from Sweden to Australia via Dubai on a 20 hour flight for a Christmas holiday I had to wonder, is running when I arrive going to help me overcome jet lag a little bit faster? It would seem logical that running outside might help you acclimatise, but is there any scientific evidence to support this?
Well yes, or kind of. There is a landmark study in this area that was undertaken in 1987 in Toronto by Mrosovsky and colleagues. The study examined the effect of running versus sleep on jet lag... sounds promising, the thing is, the study was in hamsters. Hamsters were put through an eight hour time change with one group prescribed three hours on the running wheel while the others slept. The difference in outcome was pretty profound, with the hamsters that exercised adjusting to the new time zone (phase advanced 7 hours) in an average of 1.5 days compared with 8.5 days for the sleeping hamsters. It seems that sleeping off jet lag is definitely not the cure for jet lag, at least for Hamsters.
In a second experiment, by Reebs and Mrosovsky (1989), the same study design was repeated but with the light removed while the hamsters ran on the exercise wheel. Without light, there was a lower shift in their phase advancement (2.7 hours), or the speed at which they adjusted to the new time zone. When the same hamsters were exposed to light after their activity onset, they advanced by an average of 3.3 hours. Adding the average values for activity-induced shifts and light-induced shifts gives a total of 6 hours, with possible synergism between the effects of activity and light potentially accounting for the hour difference.
So perhaps light is the most important factor then? Not running per se, but running outside and exposing yourself to light. The concept of zeitgeber (“time giver”) is a central part of physiology and the strongest zeitgeber is light itself, which can entrain physiological processes even with limited light exposure. The timing of the light signal gradually shifts as the day light (and season) changes and our bodies adjust to this shifting pattern via the zeitgeber signal. I wrote more about this in my blog about the impact of darkness on running.
Another study examined whether the time of day that you exercise affected jet lag. This time the experiment wasn´t using hamsters, it was using mice. Before I explain this one keep in mind that mice are nocturnal, so night is day for them, essentially. The mice were assigned to exercise either early or late during the night, or whenever they wanted. The mice who exercised early shifted circadian cycles like heart rate and body temperature to peak earlier in the day, while the late exercising mice shifted those same peaks to later in the day. This suggests that morning workouts might help those who are flying east like me, while afternoon workouts would help those flying west.
The results also showed that the mice running later in the night received a bigger overall boost in the functioning of their internal clocks compared to the early workout group. There was no explanation given by the researchers for this, but obviously if there is something to this then afternoon workouts could be most effective for synching your body in a new time zone. Seems like further research is needed here.
But do the findings in the hamsters and mice translate to humans? It was surprisingly difficult to find any experiments using humans so for now my answer is not sure. This might need a part II if I can find some studies in humans. Maybe no scientific group has been willing to pay a group of people to fly across the Pacific yet. Many scientific results are extrapolated from animals to humans though, so we can still learn from this.
In summary, next time you travel long distance and are going to experience some jet lag, best to find yourself a large wheel in a well lit room and go for a run, and make sure it´s in the afternoon. But seriously, it seems as though running outside in the light will definitely help you adjust, and if nothing else will ensure you are a bit more tired when you hop into bed for your first sleep in the new time zone.
Mrosovsky N and Salmon PA (1987) A behavioural method for accelerating re-entrainment of rhythms to new light-dark cycles. Nature 330:372–373
Reebs SG and Mrosovsky N (1989) Large phase-shifts of circadian rhythms caused by induced running in a re-entrainment paradigm. Journal of Comparative Physiology 165(6):819-825