Resetting one's internal clock is more complicated than simply turning back the hands. To help those struggling with jet lag, researchers have created Entrain.

Based on research from mathematicians at the University of Michigan, Entrain is designed for travellers, night-shift workers and anyone else whose circadian rhythms have been thrown out of whack. The app is available now on iOS.

The free app, designed by Olivia Walch, is based on equations developed by Danniel B. Forger and Kirill Serkh, both professors of mathematics at the University of Michigan. The two mathematicians published their findings on how math can reduce the time it takes to get over jet lag in the April 10 issue of PLOS Computational Biology.

The principle behind Entrain is based on the circadian clock, which regulates different biological functions including sleep and body temperature. Jet lag is essentially a disruption of this clock, resulting in modifications of our body temperature and sleeping and waking cycles.

Since light is the most significant factor in establishing circadian rhythms, the app uses complex equations to determine when and for how long the user should be exposed to light.

Prompted by the app, the user specifies the length of the trip, the destination city, and the brightest type of light he or she will have access to (low office lighting, bright office lighting, low daylight, bright daylight). Entrain then calculates the optimal light exposure schedule for the fastest possible adjustment, as well as providing an estimation of how long it will take to adjust.

By reducing the duration of jet lag, Entrain provides a significant health benefit. In addition to being unpleasant, jet lag can bring about more serious health problems such as depression or, in the long term, disrupted metabolism.