Monday, February 23, 2026
Let’s Stop Getting Distracted From the One Important Question About Exercise
Let’s Stop Getting Distracted From the One Important Question About Exercise
“The focus of exercise research should be on maximizing long-term adherence to fitness programs, rather than determining the “best” type or amount of exercise. Observational studies, which often confuse correlation with causation, are inadequate for answering these questions. Instead, research should prioritize understanding how to encourage sustained exercise habits, ideally through randomized trials.
By Emily Oster
Dr. Oster is the founder and chief executive of ParentData and a professor of economics at Brown University.
February is the month things go south in our exercise routines. The excitement of New Year’s resolutions fades and the dark and cold keep us in bed, rather than on the treadmill.
This is a shame, because regular exercise is really beneficial. It can control high blood pressure, improve mental health and reduce falls among older adults. A review of 187 randomized controlled trials covering nearly 30,000 people found exercise lowered mortality risk by 13 percent.
Given the fact that people struggle to stick with exercise, the crucial question is: How can we design fitness programs that maximize long-term adherence?
Unfortunately, a lot of research and media coverage is focused instead on asking what the best type of exercise or the optimal amount is. Is walking better than tennis? Is running better than swimming? Is it really important to do 80 percent of your workout at 60-70 percent of your max heart rate (known as Zone 2)? These questions serve an engaged population and promise that with a bit more knowledge, you can maximize your health. The trouble is, they are basically impossible to answer well, and most of the answers we get are misleading and wrong.
The best way to discover the optimal exercise regimen would be with large randomized trials. While we have high-quality studies comparing some exercise intervention (often a combo of aerobic exercise and weight lifting) to doing nothing, it’s far harder to find trials comparing two different types of exercise head-to-head. That’s because you’d need enormous sample sizes to detect the — most likely small — differences in a statistically meaningful way. Big trials are expensive. And not everyone wants to stick to a randomly assigned exercise program.
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Because of these challenges, most of the evidence on the so-called best exercise comes from what are known as observational studies. Instead of randomizing people to different programs, these studies ask people about the exercise they already do and compare their health outcomes to those of people who do more or less exercise, or who do different types of exercise. The trouble is that such studies almost always confuse correlation and causation.
To take a specific example: A recent paper found that swimming didn’t lower mortality, but running did. Does that mean swimming isn’t effective? No. When you look more closely at the data in the appendix of the study, it’s clear what is going on — swimmers were much less likely than runners to engage in other positive health behaviors.
For instance, only about 5 percent of frequent runners in the study smoked, but among frequent swimmers it’s 11 percent — just shy of the U.S. average. Swimmers were also more likely to have high blood pressure at base line, weigh more and have a family history of cancer. One explanation is that doctors may recommend swimming as a low-impact activity for people who already have higher health risks. Even if the swimming helps, the other differences among people hide that. (Although the authors adjust for differences in the variables they can see, there are many differences they can’t observe, and those will drive their results.)
It’s also why you should be very skeptical of the conclusion, from the same paper, that walking and running a lot are beneficial, but frequent jogging (essentially slow running or fast walking) is not. A study like this tells us plenty about the types of people who do different exercises, but that’s not actionable. People want to know what would happen if they changed their behavior.
These issues are common in exercise research. A 2019 study argued that the benefits of walking leveled off at 7,500 steps a day, suggesting that this was a threshold number. But when you look at the paper, it’s clear that the people who walk more are also more likely to do other healthy behaviors (like abstaining from smoking and eating well). A 2025 paper used wearable devices to suggest that one minute of vigorous activity is equivalent to an hour of light activity. But it doesn’t sufficiently take into account that the mere ability to engage in vigorous activity is most likely already a sign of better health, or the fact that (like with the earlier study) there are other clear differences across groups. Again, the authors make statistical adjustments to account for the differences they can see in the data, but they can’t control for all the factors associated with different exercise patterns.
I could go on. People love findings like these, but the reality is that when we see such claims we should assume that they don’t tell us much. They can even backfire — making people feel inadequate about exercise programs that are actually fine.
The limits of our knowledge are a tough pill to swallow (especially since it’s not just exercise; the research on nutrition is equally shaky). It can be frustrating to know there are some questions we’ll never answer. I also think it can be freeing, an invitation to let go of optimization and focus on what we do know. In the case of exercise, we can say with confidence that it’s good to regularly do something that raises your heart rate.
People also want to know how much exercise to do; this is also very hard to know. The randomized studies showing benefits of exercise typically aim for 2.5 hours per week. After that, we are mostly relying on lower-quality observational studies. Those show that the benefits of exercise tend to flatten around seven to 10 hours a week.
What we do know is that people are more likely to stick with an exercise program that is tailored to their preferences and lifestyle. When doctors are advising patients about exercise, they should be as open as possible to the variety of ways people might want to get moving. Research should focus on which approaches are best to lead to long-term, sustained exercise habits — ideally, research with randomized trials. The type of flawed observational research discussed above gets in the way of both of these priorities — it takes research time from studying what matters, and it creates misleading and constraining advice. It doesn’t really matter which exercise people do — they just need to do it past February.“
For Iran’s Rulers, Refusing U.S. Demands Is a Risk Worth Taking
For Iran’s Rulers, Refusing U.S. Demands Is a Risk Worth Taking
“Iran’s leaders view U.S. demands on nuclear enrichment and ballistic missiles as a greater threat to their survival than war. Despite facing economic crisis and a U.S. military buildup, Iran refuses to concede, believing U.S. pressure will only increase. Analysts warn that a new conflict seems inevitable, with Iran likely to retaliate against U.S. bases and potentially disrupt oil shipping lanes.
The government in Tehran sees capitulating to Washington’s demands on uranium enrichment and ballistic missiles as riskier to its survival than going to war, analysts say.
Facing high-stakes brinkmanship as American warships and fighter jets mass off its shores, Iran has refused to concede to President Trump’s demands on its nuclear program and weapons — a stance that has bewildered U.S. officials.
The authoritarian clerics who rule Iran see those concessions — which, in their view, could compromise their core ideology and sovereignty — as a greater threat to their survival than the risk of war.
A dangerous mismatch in perceptions between Iran and the United States is why efforts to negotiate a deal over Iran’s nuclear and military capabilities look increasingly fragile, experts say, and a new regional conflict seems almost inevitable.
“Avoiding war is indeed a high priority, but not at any cost,” said Sasan Karimi, a political scientist at the University of Tehran who served as the deputy vice president for strategy in Iran’s previous government. “At times, a political state — especially an ideological one — may weigh its place in history as heavily as, or even more heavily than, its immediate survival.”
U.S. and Iranian negotiators are struggling to break an impasse over their respective red lines.
The Trump administration says it wants Iran to agree to zero nuclear enrichment to ensure it cannot build a nuclear weapon. U.S. officials have also sometimes insisted on limiting the range of Iran’s ballistic missiles and ending the country’s support for allied militias across the region.
For Iran, which says its nuclear program is for peaceful purposes only, nuclear enrichment is a right that the supreme leader, Ayatollah Ali Khamenei, upholds and that his officials cannot abandon. And Iran sees possessing missiles that can reach as far as Israel as critical for self-defense.
U.S. and Iranian officials are set to meet in Geneva this Thursday for talks seen as a last-ditch effort to find a compromise before Mr. Trump orders a strike. According to people briefed on internal administration deliberations, the two sides will consider a proposal that offers an off-ramp to war: Allowing Iran a limited nuclear enrichment program for civilian purposes.
Mr. Trump’s administration views Tehran as so weak that it should accept U.S. demands, regional officials have said.
Last June, Iran suffered heavy blows during a 12-day war launched by Israel and briefly joined by U.S. warplanes. That conflict coupled with biting international sanctions have plunged Iran’s economy deeper into crisis.
In January, authorities used deadly force to crush nationwide protests demanding Ayatollah Khamenei’s ouster. Some smaller protests re-emerged over the weekend, demonstrating how hostile many Iranians are toward their leaders.
On top of that, the government in Tehran is facing a major buildup of U.S. firepower in the Persian Gulf, including two aircraft carrier strike groups, and a massing of reconnaissance and refueling jets across the Middle East.
Mr. Trump’s lead negotiator with Iran, Steve Witkoff, described the president as “curious as to why they haven’t” capitulated, in an interview with Fox News over the weekend.
The vice president, JD Vance, told Fox last week that despite the threat of war, Iranians “are not yet willing to actually acknowledge and work through” the president’s demands.
Yet it is the very perception of Iran’s weakness that experts say makes Tehran determined to resist.
“For Iran, submitting to U.S. terms is more dangerous than suffering another U.S. strike,” said Ali Vaez, the Iran director of the International Crisis Group. “They don’t believe that once they capitulate, the U.S. will alleviate the pressure. They believe that would only encourage the U.S. to go for the jugular.”
Ayatollah Khamenei has repeatedly stressed his view that Washington’s eventual aim is to topple Iran’s system of governance.
“Nuclear energy is not the problem, nor are human rights; America’s problem is with the very existence of the Islamic Republic,” he said in a speech in 2024.
Danny Citronowicz, an expert at the Atlantic Council who previously headed the Iran branch of Israel’s Defense Intelligence, said that beyond strategic calculations like the ballistic missiles, Ayatollah Khamenei insists on uranium enrichment as “a pillar of the regime itself.” If Iran’s leaders concede on those points, “they will actually undermine the existence of the regime itself,” he said.
“I think they don’t have any other choice than to take the bet on the military side,” he added.
Two of the main questions ahead of any potential confrontation are whether a U.S. attack would go as far as trying to topple the political system in Iran, and whether Tehran would be able to retaliate enough to make the conflict painful for Mr. Trump, too.
Tehran would probably seek to absorb limited strikes and cap its retaliation to attacks on U.S. bases in the Middle East, as it did last June, according to Farzin Nadimi, a defense analyst focused on Iran at The Washington Institute for Near East Policy, a think tank.
If Mr. Trump chooses to go further, U.S. forces, probably with the help of Israel, would have to race in the first few days to take out as much of Iran’s military capabilities as possible to hamper an attempt at a far fiercer and broader retaliation, Mr. Nadimi said.
That would require “an extensive effort both by the U.S. and Israelis — not only the air power, but also ground elements — to make sure that their missile threat is neutralized,” he said.
Iran would in turn try to mimic the success of the Houthi militia, its ally in Yemen, regional experts say.
In 2023, the Houthis derailed a U.S. military campaign that aimed to stop the group’s attacks on international shipping in the Red Sea. The group persistently attacked U.S. drones and international vessels, including an American aircraft carrier.
The 31-day confrontation cost Washington well over $1 billion, and Mr. Trump ultimately struck a deal instead of risking a drawn-out military entanglement.
Iran could try to create a protracted and deadly confrontation that could hurt Mr. Trump in a midterm election year, analysts said.
One unknown is whether Iran could launch strikes on oil tankers passing through strategic shipping lanes like the Strait of Hormuz, or have its Houthi allies strike vessels in the Red Sea, said Mohammad Ali Shabani, an Iran analyst and editor of the regional news website Amwaj.media.
If a new conflict were to drive gasoline prices up one or two dollars per gallon, that could feel very risky for Mr. Trump before midterm elections this fall, he said.
U.S. and Israeli forces could deal a quick and devastating blow, as they did last June, when a string of top Iranian military officials were killed within hours and Iran’s nuclear and military facilities were battered.
But Tehran learned lessons from that war, Iranian and regional officials say, and has prepared several layers of leadership to replace anyone killed. This aims to ensure that the system survives the conflict even if Ayatollah Khamenei and other leaders did not.
Regional officials speaking to Tehran and Washington say that if Mr. Trump chooses to strike, his aim will probably be to jolt the Iranian leadership severely enough to force it back to the negotiating table on his terms.
But several experts said that Iran refused to capitulate to U.S. terms after the last war and that if it survived another, it would probably refuse again.
“To think that a war every time either makes Iran more flexible or facilitates diplomacy is nothing but a delusion,” Mr. Vaez said.
Sanam Mahoozi and Farnaz Fassihi contributed reporting.“
What’s Happened Since the Supreme Court’s Tariff Ruling
What’s Happened Since the Supreme Court’s Tariff Ruling
“The Supreme Court ruled that President Trump’s tariffs violated federal law, striking down his use of a 1970s emergency statute to bypass Congress. In response, Trump announced a 10% global tariff on all imports, later raising it to 15%, and vowed to continue his tariff tactics despite the ruling. This decision has left trade deals uncertain, impacted American businesses and consumers, and raised concerns about the federal budget and potential refunds for collected duties.
After the Trump administration’s punishing tariffs were invalidated, the president said he would impose new tariffs using a different authority. It’s been a whirlwind.
On Friday, the Supreme Court ruled that President Trump’s sweeping tariffs on U.S. trading partners violated federal law. The ruling dealt a major blow to the administration’s economic agenda and left trade deals in limbo as world leaders tried to figure out their next steps.
Here’s what has happened since Friday:
The court’s 6-3 decision determined that Mr. Trump exceeded his authority in imposing the levies.
Chief Justice John G. Roberts Jr. wrote for the majority that the 1970s emergency statute that Mr. Trump invoked to bypass Congress did not allow him to unilaterally impose the duties.
Mr. Trump was in the East Room of the White House speaking to a group of governors and cabinet officials when he found out that the court had struck down his tariffs. He told those gathered that he had a contingency plan and ended the meeting early.
In a news conference at the White House on Friday afternoon, Mr. Trump announced a 10 percent global tariff on all imports, using a different legal authority to impose them. He also said that he would open investigations into unfair trade practices in an effort to secure additional tariffs, and that he would not reinstate the so-called de minimis exemption, a policy that had allowed billions of dollars of low-value imports to enter the United States tax-free.
Mr. Trump vowed to press forward with his tariff tactics despite the ruling. “It’s ridiculous but it’s OK. Because we have other ways, numerous other ways,” the president said on Friday. “The numbers can be far greater than the hundreds of billions we’ve already taken in.”
On Saturday, Mr. Trump said that he would raise the new global tariff rate to 15 percent, effective immediately.
Fiscal concerns swirl as experts assess the fallout from the court’s decision and the president’s reaction.
The federal budget has reached a new level of volatility. Tariffs had become a key source of revenue, and it’s unclear if Mr. Trump will be able to make up the difference to help pay for an expensive tax cut that he signed into law last year that will add to the nation’s deficit.
The fate of billions of dollars in duties collected by the United States remains up in the air. The Supreme Court has left it to the U.S. Court of International Trade and the lower courts to figure out refund proceedings. Mr. Trump was also unsure of how the process would work.
The ruling may have dashed Mr. Trump’s spending dreams, which had tariffs as their centerpiece. He had promised to use tariff revenue to offset the costs of programs that included a bailout for farmers who had faced retaliation from other countries because of his trade wars.
But Trump aides said on Sunday that the administration was on track to resurrect its punishing tariffs through a new approach that they contended would better resist legal challenges.
“The president has been campaigning on tariffs and protecting American industry for many years,” Jamieson Greer, the U.S. trade representative, said on ABC’s “This Week.” “The policy hasn’t changed.”
American businesses and consumers are unsure how any new tariffs will affect them.
American companies celebrated the ruling after enduring months of burdensome import taxes. But their relief quickly turned into newfound concern as Mr. Trump renewed his trade war with a slate of new tariffs.
A poll released on Friday that was taken before the Supreme Court’s ruling showed that 64 percent of Americans disapproved of Mr. Trump’s tariffs.
Consumers will have to wait to see how the ruling affects prices for imported products like apparel, electronics and furniture. Economists warned that any short-term boost to the economy could be hurt by a lengthy period of uncertainty.
Apple might be among the biggest winners if lower tariffs stick. While the tech giant has moved to shield itself from Mr. Trump’s trade squabbles, it has paid more than $3 billion in tariffs over the past three quarters.
In Washington, an angry President Trump is singling out those who opposed him.
Mr. Trump castigated the justices who ruled against him, calling them “fools and lap dogs” and said he would push forward with new tariffs anyway. He suggested that two he had nominated during his first term — Justices Neil M. Gorsuch and Amy Coney Barrett — were “an embarrassment to their families” because they didn’t take his side.
Mr. Trump punished a Republican lawmaker, Representative Jeff Hurd of Colorado, on Saturday by withdrawing his endorsement of the lawmaker. Mr. Hurd had joined House Democrats in voting to cancel tariffs on Canada. Mr. Trump backed Mr. Hurd’s right-wing primary opponent.
A small group of Republicans in Congress lauded the court’s ruling, including Senator Chuck Grassley of Iowa and Senator Mitch McConnell, the Kentucky Republican and former longtime party leader, who called for their branch of government to reassert its role in trade matters.
With international trade deals imperiled, world leaders look for clarity.
Countries that had struck trade deals with Mr. Trump to get lower tariff rates are now stuck with them. Last week, Japan committed to $36 billion in investments in the United States and Indonesia signed an agreement in Washington under threat of damaging levies. The court ruling has left their leaders wondering if their agreements will stand.
In Europe, officials had hoped that this year would bring stability to international trade after a chaotic 2025, but the ruling now leaves last year’s trade deal between the European Union and the United States in flux. With questions of refunds and Mr. Trump’s new unilateral tariffs, European leaders are closely watching the president’s next move.
For Canada, the most detrimental tariffs remain in place. American levies aimed at Canadian manufacturers — including the automotive, steel and aluminum industries — and the lumber sector were imposed under a different law and are unaffected by the court’s ruling.
Kim Bhasin is a business reporter covering the retail industry for The Times.“
Saturday, February 21, 2026
Do You Back Into a Parking Spot or Back Out?
Do You Back Into a Parking Spot or Back Out?
“The practice of backing into parking spaces, once uncommon, is gaining popularity in the United States. While some drivers find it safer and more convenient, others, like the author, find it unnecessary and inconvenient. The trend is partly driven by AAA’s updated guidelines, which recommend backing in for better visibility and quicker exits.
An exploration of what’s driving a change in America’s parking lots.
America, we often hear, is a deeply divided country. To our ideological divisions, allow me to add one of the vehicular kind: people who pull into a parking lot space versus those who back in.
For decades, there were generally agreed-upon standards and norms around parking. You entered a lot, saw an open spot and pulled in, like everyone else. But in the past few years, it seems to me something has changed in our national parking lots.
Listen to this article with reporter commentary
Perhaps you’ve noticed it at the supermarket or CVS. Amid all the cars that are parked headfirst, a seemingly increasing number have instead been backed in. These dissenters face out, like getaway drivers in a bank robbery ready to make a clean escape. Some people, myself included, find the move annoying.
William Van Tassel, the manager of driver training programs for AAA, confirmed my suspicion — and said that perhaps it was because they were following AAA’s updated guidelines.
“We started promoting this around 2020,” he said, in curriculum distributed to driving instructors at public and private driving schools throughout the United States.
“In general,” said Mr. Van Tassel, 59, who lives in Orlando, Fla., and drives a Porsche Cayman that he indeed backs in, “it’s a good idea from a safety perspective.”
My own theory is that reversing into a space is a response to the ambient anxiety in our society, akin to privately noting the exits in a movie theater. In a nation of rampant gun violence, backing in so you can quickly get out provides a sense of security.
Imminent Threat Solutions, a Texas-based company that teaches people to “prevail against all threats,” as its website says, recommends “tactical parking” — i.e., backing in — for swift evasion. “Next time you park somewhere, start war-gaming it,” the company suggests. “What if I was being chased?” they advise drivers to consider.
But perhaps there are more prosaic reasons, too. Some years ago, Matthew Dicks, a schoolteacher in West Hartford, Conn., noticed that a colleague would back in each morning, despite the extra time it took her to fit between parked cars.
One day, he asked her why.
“She hated her job,” Mr. Dicks, 55, said. “She told me, ‘I just want to get out of here as quickly as possible at the end of the day.’”
Although Mr. Dicks thought backing into a space was “ridiculous,” he kept an open mind, as you might if a friend said they dressed their hot dog with mayonnaise. He decided to try it for a week.
“Right away, I discovered that backing up is always harder than driving forward,” said Mr. Dicks, who wrote a blog post in 2016 laying out his arguments, including that the narrowness of a standard parking space (7.5 to 8.5 feet) relative to the width of a highway lane (12 feet) makes it more dangerous to reverse into a spot.
Mr. Dicks also believes reversing into a spot is discourteous: Other drivers must wait while you position your car, causing congestion in busy parking lots. He concluded his study with a message for his fellow drivers: “Stop backing into parking spots. It makes no sense.” (He has received multiple emails every month for several years from angry backer-inners making their case.)
Lately, I find myself doing the lazy man’s version of backing into a spot — that is, finding two open spots in a line and “pulling through” so I’m facing forward. This way, I don’t have to back up at all.
Still, like Mr. Dicks, I find reversing into a spot awkward, and I couldn’t help but wonder if there was a demographic profile of backer-inners. My wife suspects they’re mostly men showing off — was that true? And it seemed to me that a disproportionate number of them drove big American work trucks, but could you really peg backer-inners by their vehicles?
I recently drove out to the suburbs north of New York City to do a little field work. At the Ardsley Diner, in Ardsley, N.Y., amid all the cars in the lot parked the typical way, I watched Antonio Mateo back his maroon S.U.V. into a space.
Mr. Mateo, 49, who was picking up a breakfast order, said he found it easier to back in. “I get out quickly,” he explained.
Eighteen miles north, at a Home Goods in Mount Kisco, there were 38 spots in the parking lot, which was full. Five cars — or around 13 percent — were backed in. They ran the gamut of make, model and price, from a Chevrolet Trax to a Ford F-150 to a Mercedes-Benz GLK350.
The owner of the Mercedes S.U.V., Mirna Martinez, said that she started backing into spots about 10 years ago, for reasons she couldn’t remember. It has since become habit. When I asked why, she offered the same rationale I heard repeatedly.
“Convenience,” Ms. Martinez, 55, said. “It’s easier to get in and go.”
A profile was emerging, but it didn’t seem to be shaped by gender or car make — it was more of a mind-set. Backer-inners, it seemed, preferred doing the harder maneuver first. They prioritized leaving a little more quickly.
Some people, I discovered upon further investigation, are required to back into a space. Luke MacGregor, 44, is an engineer in New Brunswick, Canada.
“I do a lot of work at industrial sites, like power plants, refineries,” he said. “Our corporate policy is to back in. The idea is if there was any reason to leave quickly, like an evacuation, everyone could get out a little faster.”
Mr. MacGregor’s 81-year-old mother, Sandra Phinney, appears to back in — but she actually pulls through, as I do, because craning her neck is painful, she wrote in an email. “It’s much easier to drive straight out.”
And safer, as Mr. Van Tassel, the AAA instructor, said. He cited a 2020 study from the journal Transportation Research that found, among other things, that the pull-in, back-out maneuver had a higher crash risk. Since pedestrians are most likely to be found walking in the major lanes, not in a parking space, it’s safer to back into the area with fewer people. This was a major factor in the updated AAA recommendation, he said.
So now that backing into a space is doctrine, it seems likely the practice will proliferate.
But I can’t bring myself to join in, and I don’t fully accept the safety argument. Since 2018, new vehicles sold in the United States have been federally mandated to have backup cameras, which can assist in reversing out of a spot without plowing into someone.
Mr. Dicks is firmly in my camp. Indeed, it has become something of a small crusade to convince the fellow drivers in his life not to back in.
Not long ago, Mr. Dicks rode with a friend to Boston for a night out.
“We arrived and he was pulling into a parking lot, and I saw he was lining up to back in,” he said. “I said, ‘No! What are you doing?’ He tells me, ‘I thought we could save time, get out quicker.’ What are we going to save? One second in a day?”
And, thus, the friend pulled in.“
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