There's possibly no better feeling than the calm and happiness that follow the completion of a long, tough run.

So where does this this so-called "runner's high" come from?

You've probably heard it get chalked up to a rise in endorphins, the "happy" chemicals that induce feelings of pain relief and pleasure. But it's actually more complicated than that. 

The 'endorphins make you happy' idea

The idea that increased levels of endorphins are responsible for that post-workout happy feeling came out of 1980s research that showed endorphin levels in the blood spiked after prolonged exercise. Some researchers assumed these chemicals must also produce the sense of euphoria we feel after a workout.

But recent studies in mice suggest that endorphins actually might not have anything to do with the runner's high. The problem with the endorphin explanation is that they're very large molecules — so large, in fact, that they can't move from the blood into the brain.

The blood-brain barrier is key to keeping the brain safe, since it stops certain pathogens and molecules from passing from the blood into the brain. Because endorphins can't get through, it's unlikely that they are the sole chemical responsible for the feelings associated with vigorous exercise.

Instead, scientists think the effect can be attributed to other chemicals in the body that produce similar pain-relieving and happy feelings.

Turning to endocannabinoids

Levels of a chemical called anandamide also increase when you exercise, according to a 2015 study in mice and a small 2004 study in people. Anandamide is a type of endocannabinoid, a chemical that's part of the system that moderates the psychoactive, feel-good effects of marijuana. And unlike cumbersome endorphins, anandamide can smoothly make its way from the blood to the brain. 

For the 2015 paper, researchers at the Central Institute of Mental Health at the University of Heidelberg medical school compared the effects of endorphins and endocannabinoids on mice as they ran on running wheels.

The researchers found that, in addition to appearing more calm less sensitive to pain after running, the mice had higher levels of both endorphins and endocannabinoids. The animals also spent more time in well-lit parts of their cage, something calm, less anxious mice tend to do. They were also slightly more pain-tolerant after their stints on the wheel.

To measure the effects of each chemical individually, the researchers gave the mice drugs that blocked the effects of each. When they blocked the endorphins, nothing happened — the animals remained more relaxed and pain-tolerant. But when they blocked the effects of the endocannabinoids, the symptoms of the mice's runner's highs disappeared. 

These findings suggest that the mice's elevated endorphin levels had little to do with their post-workout buzz.

This research has one obvious caveat, however: Mice aren't humans. And the study also revealed, disappointingly, that you probably need to run pretty far to experience a runner's high. The mice ran an average of more than three human miles per day (a long way for a mouse).

If you're interested in learning more about the connection between endocannabinoids and runners' highs, this video from YouTube channel SciShow walks through some of the evidence.

Other factors at play

Other studies, however, suggest that neither endorphins nor endocannibinoids are the cause of the runner's high. A 2015 study, for example, found that mice with low levels of a hormone called leptin tended to run farther than mice with normal levels of leptin.

Leptin, otherwise known as the "satiety hormone," inhibits the feeling of hunger in order to regulate our energy levels. The idea is that the less full (or more hungry) you feel, the more motivated you are to keep running. And that increased motivation might make it easier to get a runner's high.

"Ultimately, leptin is sending the brain a clear message: When food is scarce, it’s fun to run to chase some down," lead study author Maria Fernanda Fernandes told Outside Magazine in 2015.

But again, the fact that these results have been demonstrated in mice doesn't mean the same effects will necessarily be found in humans. And because there might be a combination of factors at play, definitive evidence of what exactly causes a runner's high might continue to elude scientists for a while.

An earlier version of this post was written by Tanya Lewis. 

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July 1 is Canada Day, a federal holiday celebrating the unification of Canada's three colonies 150 years ago.

For many people, it may also be a reminder that Canada is a land where healthcare is free, people are friendly, and Prime Minister Justin Trudeau explains quantum computing just for laughs.

If all that has Canadian citizenship looking pretty tempting, you'll first need to go through several steps, like living in the country for at least six years, staying on your best behavior, and knowing a thing or two about the country you'll soon call home.

For those who actually want to head up north, here's how you move to Canada.

SEE ALSO: How to move to Sweden and live in the future

Preface: Make sure you're not already a Canadian citizen.

Before you go through the hassle of applying for citizenship, take a short quiz to see if you may already be Canadian.

The government outlines several caveats for being a citizen even if you weren't born there, many of which depend on your parents' citizenship. Maybe you secretly inherited their status at some point along the way.

Be at least 18 years old.

If you're not a legal adult, you've got an uphill climb ahead of you.

Minors need their parent or legal guardian to fill out the application for them; they need to be permanent residents in Canada (more on that later); and the parent must either be a citizen or applying to become one at the same time.

Or enter the pool for skilled immigrants.

Canada has a fast-track system for immigration called Express Entry. It's how skilled workers transition into a role in the country.

All applicants into Express Entry are given specific scores based on their specific talents and job prospects and then ranked with other applicants. Those at the top of the rankings are invited to become permanent residents.

Sales of recreational marijuana kick off in Nevada on Saturday, July 1, and the state is expecting on onslaught of tourists coming to sample the local merchandise.

But visitors might have tough times finding the drug in stores.

Anyone who is 21 and over with a valid ID can buy up to an ounce of pot (or one-eighth of an ounce of edibles or concentrates) from one of several medical marijuana dispensaries that have been approved for recreational sales.

State regulators have issued the licenses necessary to 37 retail outlets in Las Vegas and unincorporated Clark County, as of June 29, the Las Vegas Review-Journal reported.

In a legal snafu, those stores may sell the marijuana they have in stock for recreational use, but may not resupply their inventory and sell the new stuff to non-medical users. Their stock may run out as early as August, leaving recreational users without a place to buy their legal bud.

Alcohol wholesalers have the exclusive rights to move recreational marijuana from growers to retailers in Nevada, as part of a temporary court order that was extended by a Carson City district judge in June. Nevada intends to appeal the order, so that the state's medical marijuana dispensaries can obtain pot distribution licenses, according to the Associated Press.

Nevada is the only state with legalized marijuana that has such an arrangement.

In addition to Nevada, voters in Colorado, Washington, Alaska, Oregon, California, Maine, Massachusetts, and the District of Columbia have legalized recreational use of the drug.

It became legal to possess up to an ounce of pot in Nevada and use it in private residences on January 1. Before then, residents needed a medical card to shop at dispensaries.

Tourists are expected to make up 63% of recreational pot sales, Nevada officials told the Associated Press. More than 40 million people visited Las Vegas in 2016.

SEE ALSO: Here's where you can legally smoke weed now

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We visited Steak 'N Shack - an American food chain hailing from Illinois. Here's why we think it's one of the most underrated chains in America.

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Making a habit of eating out at restaurants is quick way to bust your budget. Cooking at home is almost always going to be cheaper. 

That's especially true in major, cosmopolitan cities like Tokyo, Oslo, and Zurich, where dinner for two at a regular neighborhood restaurant — not even a fancy establishment — will run you over $60. In 15 other cities around the world it will cost at least $40. 

That's according to a recent report by Deutsche Bank, which analyzes the cost of living and compares prices among the largest cities around the world. 

The report sources prices from Expatistan, a site that tracks cost-of-living expenses in over 200 countries, for a "basic dinner at a neighborhood pub for two" in nearly 50 cities. 

Here are the 18 most expensive cities in the world for eating dinner out at a restaurant. 

All prices are in US dollars.

SEE ALSO: The 16 most expensive cities in the world for commuting to work

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18. Singapore — $40.20

17. Helsinki, Finland — $40.70

16. Toronto, Canada — $40.90

Macy's Fourth of July Spectacular has become one of the largest firework displays in the United States. This year, over 60,000 fireworks will go off over New York City's skyline. Here's what it takes to set it all up.

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The US president's relationship with the press has long been a complicated one, and it has varied from administration to administration. To name just a few examples, President Lyndon B. Johnson attempted to thwart certain stories from going to press, while President Gerald Ford was friendly with journalists and even invited some to White House state dinners. 

The Associated Press has been documenting the lives of presidents since the early 1930s, capturing candid moments of each commander-in-chief since President Franklin D. Roosevelt.  

From press briefings to interviews aboard Air Force One, here are 14 AP photos of presidents interacting with the press.

SEE ALSO: Here's everything we know about Trump's 26-year-old personal assistant

President Franklin D. Roosevelt would invite members of the press into the Oval Office for briefings twice a week.

Source: The New York Times

Press briefings don't come to a halt while the president is on vacation. Here, Harry S. Truman had the press visit his Winter White House in Key West, Florida.

It was President Dwight D. Eisenhower's press secretary, James Haggerty, that established some still-standing traditions between the president and the press, like regularly scheduled news conferences.

Source: The New York Times

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In a blind taste test, we had Business Insider employees try french fries from McDonald's, Wendy's, Shake Shack, Chick-fil-A, and Burger King. Each fry was a bit different in texture, shape, and size, but one fry reigned supreme. 

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Next to housing, transportation is one of the largest recurring expenses people face. In a major metropolis, that likely means a fair amount of time packed into the subway, trolley, or bus getting a little too acquainted with your fellow city dwellers.

The good news: It's better for the environment, and, depending on where you live, it may be cheaper than owning a car. 

The bad news: It can still be really expensive. 

In London, the most expensive city in the world for public transportation, you'll need to shell out nearly $175 for a month of riding the Tube. In New York City, a monthly transit pass costs about $120. 

That's according to a recent report by Deutsche Bank, which analyzes the cost of living and compares prices among the largest cities around the world. 

The report sources prices from Expatistan, a site that tracks cost-of-living expenses in over 200 countries, for a "monthly ticket public transport" in nearly 50 cities. 

Here are the 16 most expensive cities in the world for commuting via public transportation each month.

All prices are in US dollars.

SEE ALSO: The 24 most expensive cities in the world to grab a beer at the local bar

16. San Francisco, United States — $86.10

15. Berlin, Germany — $87.20

14. Frankfurt, Germany — $88.50

60 year-old Take-Two Interactive CEO Strauss Zelnick is in insane shape for any age, let alone his own. He works out between seven and 12 times a week, and he founded a group fitness club called The Program.

Strauss invited us to shadow him during what he calls "the V-shape workout" at Equinox Tribeca. The 50-minute workout focuses on strengthening core and upper body muscles.

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The best grocery chain in the US is one that most Americans have never visited. 

In fact, Wegmans, which has fewer than 100 locations, gets thousands of calls per year from people begging for a store to open in their hometown. 

Wegmans has ranked number one in Market Force Information's annual survey of the best grocery stores for the last two years thanks in large part to its loyal fans. 

But we, like many other Americans, had never been to a Wegmans, so on a recent trip to Charlottesville, North Carolina, we knew we had to visit one. 

Here's what it was like:

Driving up to the Wegmans in Charlottesville, North Carolina, it was immediately clear that this wouldn't be a normal shopping trip.

The impressive attributes of the store shouldn't have come as a surprise. Wegmans was voted the best grocery chain in the US in 2017, based on Market Force Information's annual survey of the industry.

It was when we walked into the store, however, that we realized Wegmans isn't just large — it's a behemoth.

Vacations are an essential part of staying productive and happy at work.

Most Americans could seriously use more time off.

Like any major life event, vacations deserve some thoughtful planning.

That's why the week before your big trip is crucial. If you dart out for a week or two without any preparation, you could find yourself swamped when you get back.

Fortunately, there are numerous steps you can take ahead of time to curb potential problems.

Here are several things you should do the week before your vacation starts:

DON'T MISS: 12 signs you desperately need a vacation from work

DON'T MISS: 7 things successful people do the night before a vacation

Schedule some wiggle room for yourself

Instead of diving straight into your vacation and then jumping back into work, leave yourself some room to breathe.

Michael Kerr, an international business speaker and author of "The Humor Advantage," tells Business Insider:

"If your work situation permits it, leave a day after you've 'officially' booked off and arrive a day before you've announced your official return. This buys you an extra distraction-free day at both ends of your vacation so that you leave feeling better prepared and more relaxed and return to work without feeling overwhelmed."

Talk to everyone you work with

Before you leave on your summer adventure, you've got to fill in your customers.

Kerr says:

"Contact any high-priority clients before going to make sure you've answered any questions and addressed their needs before heading out. It's not only a great customer service habit to get into, it will give you greater peace of mind. It also gives you a simple but legitimate excuse to reach out to clients you may not have talked to in a while."

Don't forget about reaching out to your coworkers too.

Lynn Taylor, a national workplace expert and the author of "Tame Your Terrible Office Tyrant: How to Manage Childish Boss Behavior and Thrive in Your Job," tells Business Insider:

"Create a game plan of who you must meet or communicate with regarding your plans. Begin creating an email for all relevant parties so work will be uninterrupted and your team can fill in for you — with all key information handy."

Lastly, make sure to pass on relevant passwords, projects, and deadlines to your colleagues. It's better to do this at the start of the week, so you're not dumping a ton of information into anyone's inbox on a Friday afternoon as you rush to the airport.

Prioritize your tasks

Try to prioritize your days so that you can complete major tasks before you leave.

Ryan Kahn, a career coach, founder of The Hired Group, and author of "Hired! The Guide for the Recent Grad," tells Business Insider:

"Close out any outstanding projects. Your time off during the vacation is there for you to recharge and refresh. Don't leave loose ends or missed deadlines lingering over you. Spend the extra time now to make sure you can enjoy worry-free time off."

But make sure the week before you head off on a vacation isn't too jam-packed with busy work — you want to focus on the important stuff.

"Accept the fact that you will never get everything cleared off your plate before leavening — so prioritize and plan carefully to ensure you can leave with a clear a head as possible," Kerr says.

Taylor and Kerr agree that having a plan of action for when you get back is also important. You want to have your priorities straight once you're back from vacation.

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Wearing a full face of makeup or a $5,000 custom-fit suit might very well make you more attractive — for a day.

If you're looking to make yourself more appealing for the long term, focus on developing a stellar personality.

Business Insider asked a panel of dating and relationship experts for their best tips on becoming more attractive — without changing your physical appearance. Each one came up with creative and easy-to-implement strategies that will help you a) score a date and b) cultivate a lasting relationship.

Read on to learn how to become the very best version of yourself.

SEE ALSO: The 8 most attractive qualities people look for in a partner

Be more interested; be less interesting

That's according to Hal Runkel, marriage and family therapist and author of "Choose Your Own Adulthood." Specifically, he recommends: "Ask more follow-up questions about others, instead of impressing with stories about yourself."

Helen Fisher, biological anthropologist and author of "The Anatomy of Love," said much the same thing: "Ask a potential partner about himself or herself. Most people enjoy those who are curious about them and are likely to find you more attractive, friendly, and interesting."

Diversify your experiences

"When you have a wide range of interests outside of work and an eclectic group of friends, you’re naturally more fascinating to potential partners," said Joseph Burgo, psychotherapist and author of "The Narcissist You Know."

"Workaholics and people who take little interest in the world around them make poor conversationalists and bring little to the relationship table."

Smile

"It’s a sure way to make yourself more attractive to others," Fisher said.

"When you smile, those who see your smile, smile back, even if very briefly. And as they smile, they use facial muscles which trigger the release of neurochemicals in their brain associated with feelings of pleasure — and they are thus likely to feel happy in your company.

"So smile: It’s cheap, easy and a primordial mechanism for making friends and finding a mate."

It's Canada's birthday!

July 1, also known as Canada Day, marks the 150th anniversary of the confederation. An estimated half a million people are expected to attend celebrations in the capital Ottawa, where the government spent approximately half a billion Canadian dollars (US $386 million) on the festivities.

See how Canadians and a couple of royal visitors celebrated.

SEE ALSO: How to move to Canada and become a Canadian citizen

Prime Minister Justin Trudeau kicked off the festivities in a visit with Prince Charles, whose mother, the Queen, remains Canada's head of state 150 years after its independence.

Prince Charles and his wife Camilla spent the last several days visiting museums, monuments, and even startups in Canada. July 1 marks the end of their royal tour.

The Duchess of Cornwall greeted onlookers outside the Canadian Museum of History.

Take control of the tongs with these tips from butcher Jason Wachtelhausen of Harlem Shambles. 

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We all know we're supposed to wear sunscreen to protect our skin. But how does sunscreen work? What does SPF mean? Here's everything you need to know before you hit the beach this summer.

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Everyone wants a pair of sunglasses they'll look cool in — but not everyone knows how to go about buying one.

There's lots of confusing information out there about face shapes and frames. We took the six most common face shapes and gave our professional recommendation for each one. 

Most faces will fit one of these shapes, so figuring out which one is most like yours should be easy with the help of this graphic.

SEE ALSO: 17 things every guy needs in his closet for summer

With company cultures that celebrate—and even encourage—employees bringing their dogs to work, it's no wonder that many of tech's biggest players are also parents to the cutest creatures known to man. 

From Google to Salesforce, dogs have taken over the hearts and Instagrams of the industry's most powerful leaders. Sure these people are setting the agenda for global business and politics, but even billionaires need a little TLC (tender loving cuddles). 

And did we mention these dogs are darn cute? Here's a round up of some of the tech industry's most powerful dogs.

SEE ALSO: HubSpot is going to give one lucky person $100,000 to start his or her dream business

This is Beast, Mark Zuckerberg's excessively woolly Puli

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Facebook CEO Mark Zuckerberg and his wife Priscilla Chan adopted Beast in 2010. Their daughter Max, who was born in 2015, has grown quite attached to the pup.

This is Teddy, step-dog to Evan Spiegel, the co-founder of Snapchat.

When Spiegel married model Miranda Kerr, he became stepdad to her son — and to her cuddly pup, Teddy. Spiegel is rarely seen in public with the dog, but it's rumored that Teddy made an appearance in Spiegel's L'Uomo Vogue photo shoot. You be the judge.

If you follow Lyft's former chief marketing officer on Instagram, then you know her dog well

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Kira Wampler, the CEO of Art.com and former CMO of Lyft, keeps her followers up-to-date on her dog's hilarious sleeping positions. You can't say Wampler doesn't know art when she sees it.