Skip to main content
The Globe and Mail
Support Quality Journalism.
The Globe and Mail
First Access to Latest
Investment News
Collection of curated
e-books and guides
Inform your decisions via
Globe Investor Tools
per week
for first 24 weeks

Enjoy unlimited digital access
Cancel Anytime
Enjoy Unlimited Digital Access
Canada’s most-awarded
newsroom for a reason
Stay informed for a
lot less, cancel anytime
“Exemplary reporting on
COVID-19” – Herman L
per week
for 24 weeks
Get full access to
Just $1.99per week for the first 24weeks
Just $1.99per week for the first 24weeks
var select={root:".js-sub-pencil",control:".js-sub-pencil-control",open:"o-sub-pencil--open",closed:"o-sub-pencil--closed"},dom={},allowExpand=!0;function pencilInit(o){var e=arguments.length>1&&void 0!==arguments[1]&&arguments[1];select.root=o,dom.root=document.querySelector(select.root),dom.root&&(dom.control=document.querySelector(select.control),dom.control.addEventListener("click",onToggleClicked),setPanelState(e),window.addEventListener("scroll",onWindowScroll),dom.root.removeAttribute("hidden"))}function isPanelOpen(){return dom.root.classList.contains(}function setPanelState(o){dom.root.classList[o?"add":"remove"](,dom.root.classList[o?"remove":"add"](select.closed),dom.control.setAttribute("aria-expanded",o)}function onToggleClicked(){var l=!isPanelOpen();setPanelState(l)}function onWindowScroll(){window.requestAnimationFrame(function() {var l=isPanelOpen(),n=0===(document.body.scrollTop||document.documentElement.scrollTop);n||l||!allowExpand?n&&l&&(allowExpand=!0,setPanelState(!1)):(allowExpand=!1,setPanelState(!0))});}pencilInit(".js-sub-pencil",!1); // via darwin-bg var slideIndex = 0; carousel(); function carousel() { var i; var x = document.getElementsByClassName("subs_valueprop"); for (i = 0; i < x.length; i++) { x[i].style.display = "none"; } slideIndex++; if (slideIndex> x.length) { slideIndex = 1; } x[slideIndex - 1].style.display = "block"; setTimeout(carousel, 2500); } //

Getty Images/iStockphoto

Back in 1987, University of Toronto researcher Dr. Nicholas Mrosovsky put a group of hamsters through an eight-hour time change, and then made half of them run on an exercise wheel in the new time zone while the others slept. The result: The exercised hamsters adjusted to the new time zone in 1.5 days on average, while the sleepers took 8.5 days.

If you could put that result into a pill, it would be a best-seller.

But humans aren't hamsters, and for more than two decades, researchers have struggled to turn Mrosovsky's initial observation into a usable prescription for resetting your body's internal clock. Now a series of new studies offers fresh clues about how regular, strategically scheduled exercise can help you adjust to new time zones – and perhaps, more importantly, strengthen circadian rhythms that weaken as we age.

Story continues below advertisement

The recent switch to daylight time was a reminder that adjusting your internal clock can be a difficult and sometimes unpleasant task. Rotating shift workers and frequent travellers know this all too well – but all of us experience progressively weakening internal rhythms as we get older, disrupting sleep schedules and making it harder to bounce back from time shifts. The stakes are high: Persistent disruptions in circadian rhythms are linked to diabetes, cancer progression, memory and cognition problems, and a host of other health concerns.

One of the key questions that remain unanswered is what time of day is best to exercise. Researchers from UCLA tackled this issue in a study published in the Journal of Physiology, in which they assigned mice to exercise either early or late during the night, or whenever they wanted. (Since mice are nocturnal, their night hours are analogous to human daytime hours.)

As you might expect, early exercise shifted circadian cycles like heart rate and body temperature to peak earlier in the day, while late exercise shifted those same peaks to later in the day. This suggests that morning workouts might help those who are flying east, while afternoon workouts would help those flying west.

More surprisingly, the results showed that the mice working out later in the night received a bigger overall boost in the functioning of their internal clocks compared to the early workout group – a result that the researchers were unable to explain. Could it be that, in humans, afternoon workouts are most effective for synchronizing your body in a new time zone? Only further studies will tell, the researchers say.

Despite the unanswered questions, a forthcoming study in the journal Age offers a more practical message. Researchers from Amherst College, Mass., compared the function of the "suprachiasmatic nucleus," or SCN – the body's central timekeeper, located in the brain – in young and old mice, and saw significant differences.

"We think that the output signal from the SCN is weakened by aging," explains Dr. Mary Harrington, the senior author of the study.

In other words, the clock is still ticking properly, but its message isn't reaching the rest of the body as effectively as it used to. But when the mice were given regular access to an exercise wheel, this age-related decline in SCN function was slowed, and even at the geriatric-for-mice age of 18 months, they were able to adjust more quickly following an eight-hour time change.

Story continues below advertisement

The use of targeted workouts at specific times to tackle jet lag remains an open question, but Harrington's research points to a much more broadly applicable message: Regular, consistent exercise will keep your circadian clock ticking strongly, helping you adjust to time changes and protecting you from a subtle but damaging side-effect of aging.

In the battle against wayward internal clocks, sleeping pills, sedatives and hormones like melatonin are often deployed with limited and variable success. As Mrosovsky and his co-author Peggy Salmon wrote in their seminal paper 26 years ago, "For the fit and pharmacologically conservative, jogging might be preferable to drugs."

Editor's note: An earlier version of this article stated the wrong directions when advising travellers of when to exercise. This has been corrected.

Tips to keep your clock ticking

Exercise regularly at a time that's comfortable for you. Avoid exercise after 11 p.m.

Restrict your eating to a 12-hour period during the day – for example, 7 a.m. to 7 p.m.

Story continues below advertisement

Avoid light exposure, such as bright electronic screens, just before bed and at night.

Alex Hutchinson blogs about exercise research at His latest book is Which Comes First, Cardio or Weights?

Your Globe

Build your personal news feed

  1. Follow topics and authors relevant to your reading interests.
  2. Check your Following feed daily, and never miss an article. Access your Following feed from your account menu at the top right corner of every page.

Follow the author of this article:

View more suggestions in Following Read more about following topics and authors
Report an error Editorial code of conduct
Due to technical reasons, we have temporarily removed commenting from our articles. We hope to have this fixed soon. Thank you for your patience. If you are looking to give feedback on our new site, please send it along to If you want to write a letter to the editor, please forward to

Welcome to The Globe and Mail’s comment community. This is a space where subscribers can engage with each other and Globe staff. Non-subscribers can read and sort comments but will not be able to engage with them in any way. Click here to subscribe.

If you would like to write a letter to the editor, please forward it to Readers can also interact with The Globe on Facebook and Twitter .

Welcome to The Globe and Mail’s comment community. This is a space where subscribers can engage with each other and Globe staff. Non-subscribers can read and sort comments but will not be able to engage with them in any way. Click here to subscribe.

If you would like to write a letter to the editor, please forward it to Readers can also interact with The Globe on Facebook and Twitter .

Welcome to The Globe and Mail’s comment community. This is a space where subscribers can engage with each other and Globe staff.

We aim to create a safe and valuable space for discussion and debate. That means:

  • Treat others as you wish to be treated
  • Criticize ideas, not people
  • Stay on topic
  • Avoid the use of toxic and offensive language
  • Flag bad behaviour

If you do not see your comment posted immediately, it is being reviewed by the moderation team and may appear shortly, generally within an hour.

We aim to have all comments reviewed in a timely manner.

Comments that violate our community guidelines will not be posted.

UPDATED: Read our community guidelines here

Discussion loading ...

To view this site properly, enable cookies in your browser. Read our privacy policy to learn more.
How to enable cookies