Entrain Yourself

Monitor your body's circadian clock using your smartphone. Adjust faster to new time zones and schedules.

Video links:     Entrain V3.0 Trailer             How to Beat Jet Lag

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Entrain is a free app that connects users to lighting schedules developed by researchers at the University of Michigan. These schedules are mathematically proven to adjust you to new time zones as quickly as possible. Light is the primary driving input to the circadian clock, and by recording your lighting history, we can simulate your body's clock and make recommendations for behavior.

Frequently Asked Questions

  • Q. Why is the app called Entrain?

  • A. Entrainment is the 'alignment of an organism's circadian rhythm to that of an external rhythm in its environment.' It's a technical term, but it also captures exactly what the app is trying to do: entrain you to a new schedule.
  • Q. What are circadian rhythms?

  • A. The word circadian comes from the Latin "circa," about, and "diem," a day. So, circadian rhythms are biological rhythms that repeat themselves about once a day. Many, many things in your body have a circadian rhythm, including your body temperature, your immune system; even your hand's grip strength.
  • Q. Why is light so important?

  • A. Light is the primary signal to the circadian clock. A lot of things, like food and movement, can also drive the circadian clock, but light has the most dominant influence. By tracking your light exposure, we can approximate where you are in your daily cycle. Similarly, by exposing yourself to light at the right times, we can steer your body's clock to a new time zone, faster.
  • Q. How do I use Entrain?

  • A. Think of the app as a mirror of what your body is experiencing. When you first set up the app, it asks several questions to try to figure out what time your body thinks it is at that moment. From that point on, the app uses the light you report to track your clock, and all trips are defined using where the app thinks you are in your daily rhythm as a starting point.
  • Q. Who made Entrain?

  • A. The original optimal schedules were developed by Kirill Serkh, then a Master's student at the University of Michigan (now a Ph.D student at Yale), and Danny Forger, a Professor of Mathematics at UoM. Revised optimal schedules were developed by Sam Christensen of the University of Michigan. Additional algorithms for the app were created by Olivia Walch, now a post-doc at Michigan, who also designed and coded the app. She can be reached at entrainorg@umich.edu.
  • Q. Where do the recommended schedules come from?

  • A. The schedules are computed using techniques from the theory of optimal control. The big idea is that, given equations describing the human circadian clock, we can ask what light stimulus moves that clock from one ``phase'' to another in the least amount of time. A detailed explanation of the math involved can be found in the paper presenting the schedules, available here.
  • Q. What if I can't follow the lighting schedule provided?

  • A. Sometimes the app will recommend darkness when your own schedule requires light! Other times, it might recommend very bright light during the night. The 'Calendar' page of the app lets you update your lighting history to reflect what you actually experienced to get a new recommended schedule. You can also try blocking the light with orange-tinted glasses to approximate darkness or using a 10,000 lux lamp inside to simulate full daylight.
  • Q. What if I forget to schedule a return trip and the app still thinks I'm in an old destination?

  • A. You can reset the app to reflect your current time zone by either scheduling a return trip on the Trips page or using the Settings page to update your timezone and schedule. Neither of these will take effect immediately (they'll try to adjust you using an optimal schedule), so if you need to reset your schedule right away, the fastest approach is to reset the app in Settings.
  • Q. What mathematical models are used in Entrain?

  • A. The circadian clock is modeled using the equations in Forger et al., 1999. Sleep drive is modeled as a flip-flop system using a modified form of equations developed by Dr. Victoria Booth and Dr. Cecilia Diniz Behn.
  • Q. Will Entrain help me sleep better during travel?

  • A. Entrain's goal is to help you get your clock to the right time zone quickly. Doing this should help you start sleeping better, faster, in the new time zone. Many other factors that we aren't accounting for can affect sleep, however, so if you feel like you need to sleep during an adjustment, you can simply update your lighting history on the Schedule page to get new recommendations.
  • Q. What happens if I choose to submit my data?

  • A. For Android: If you click the 'Submit Data' button on the 'Submit' page, your lighting history, travel schedule, jetlag ratings, and responses to the demographics questions will be sent to servers at the University of Michigan anonymously. For iOS: If you choose to opt-in during the app set-up, your anonymized lighting history, travel, survey responses, and demographics are collected. No data is collected without your consent. The data submitted will be used to help us test and improve the schedules we recommend. Our privacy policy in full can be found here.
  • Q. Where can I learn more?

  • A. There are a lot of misconceptions about sleep and circadian rhythms floating around out there. A great starting point for learning more about sleep science is Harvard's Sleep and Health Education Program.


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Get in Touch

Questions and comments about Entrain can be directed to entrainorg@umich.edu, or to the University of Michigan Mathematics Department at:

East Hall
530 Church Street
Ann Arbor, MI 48109