SAN FRANCISCO — It’s 1 p.m. on a Thursday. Dianne Bates, 40, juggles耍弄 three screens. She listens to a few songs on her iPod, then taps out a quick e-mail on her iPhone and turns her attention to the high-definition高清 television.

Just another day at the gym.

As Ms. Bates multitasks, she is also churning搅动 her legs in fast loops圈 on an elliptical椭圆 machine in a downtown繁华 fitness健身 center. She is in good company. In gyms and elsewhere, people use phones and other electronic devices to get work done — and as a reliable antidote解毒 to boredom.

高科技的好处

Cellphones, which in the last few years have become full-fledged羽翼丰满 computers with high-speed Internet connections, let people relieve the tedium（tediousness) of exercising, the grocery store lines排队, stoplights交通管制红绿灯 or lulls in the dinner conversation.

The technology makes the tiniest windows of time entertaining, and potentially productive.

坏事

But scientists point to an unanticipated side effect: when people keep their brains busy with digital input, they are forfeiting丧失 downtime休息 that could allow them to better learn and remember information, or come up with new ideas.

Ms. Bates, for example, might be clearer-headed if she went for a run outside, away from her devices, research suggests.

downtime lets the brain go over

At the University of California, San Francisco, scientists have found that when rats have a new experience, like exploring an unfamiliar area, their brains show new patterns of activity. But only when the rats take a break from their exploration do they process those patterns in a way that seems to create a persistent memory of the experience.

The researchers suspect that the findings also apply to how humans learn.

“Almost certainly, downtime lets the brain go over 温习experiences it’s had, solidify them and turn them into permanent long-term memories,” said Loren Frank, assistant professor in the department of physiology at the university, where he specializes in learning and memory. He said he believed that when the brain was constantly stimulated, “you prevent this learning process.”

At the University of Michigan, a study found that people learned significantly better after a walk in nature than after a walk in a dense urban environment, suggesting that processing a barrage of information leaves people fatigued.

假象

Even though people feel entertained, even relaxed, when they multitask while exercising, or pass a moment at the bus stop by catching a quick video clip, they might be taxing疲劳 their brains, scientists say.

“People think they’re refreshing themselves, but they’re fatiguing themselves,” said Marc Berman, a University of Michigan neuroscientist.

见缝插针，时间像海绵

Regardless, there is now a whole industry of mobile software developers competing to help people scratch搔 the entertainment itch痒痒. Flurry, a company that tracks追逐 the use of apps（A computer application）, has found that mobile games are typically played for 6.3 minutes, but that many are played for much shorter intervals. One popular game that involves stacking 堆放blocks gets played for 2.2 minutes on average.

Today’s game makers are trying to fill small bits of free time, said Sebastien de Halleux, a co-founder of PlayFish, a game company owned by the industry giant Electronic Arts.

“Instead of having long relaxing breaks, like taking two hours for lunch, we have a lot of these micro-moments,” he said. Game makers like Electronic Arts, he added, “have reinvented改造 the game experience to fit into micro-moments.”

Many business people, of course, have good reason to be constantly checking their phones. But this can take a mental toll代价、损耗. Henry Chen, 26, a self-employed auto mechanic in San Francisco, has mixed feelings不可分割，情结 about his BlackBerry habits.

“I check it a lot, whenever there is downtime,” Mr. Chen said. Moments earlier, he was texting with a friend while he stood in line at a bagel麻花 shop; he stopped （playing game ) only when the woman behind the counter interrupted him to ask for his order.

Mr. Chen, who recently started his business, doesn’t want to miss a potential customer. Yet he says that since he upgraded his phone a year ago to a feature-rich多姿多彩 BlackBerry, he can feel stressed out难受死了 by what he described as internal pressure to constantly stay in contact.

客观需要和心理欲望的区别

“It’s become a demand. Not necessarily a demand of the customer, but a demand of my head,” he said. “I told my girlfriend that I’m more tired since I got this thing.”

人生是负累

事业使人累，游戏更使人累。人生的负累太多，善，更是负累。

In the parking lot outside the bagel shop, others were filling up moments with their phones. While Eddie Umadhay, 59, a construction inspector, sat in his car waiting for his wife to grocery shop, he deleted old e-mail while listening to news on the radio. On a bench outside a coffee house, Ossie Gabriel, 44, a nurse practitioner, waited for a friend and checked e-mail “to kill time.”

Crossing the street from the grocery store to his car, David Alvarado pushed his 2-year-old daughter in a cart filled with shopping bags, his phone pressed to his ear.

He was talking to a colleague about work scheduling, noting that he wanted to steal a moment to make the call between paying for the groceries and driving.

“I wanted to take advantage of the little gap,” said Mr. Alvarado, 30, a facilities manager at a community center.

For many such people, the little digital asides come on top of heavy use of computers during the day. Take Ms. Bates, the exercising multitasker at the expansive Bakar Fitness and Recreation Center. She wakes up and peeks at her iPhone before she gets out of bed. At her job in advertising, she spends all day in front of her laptop.

But, far from wanting a break from screens when she exercises, she says she couldn’t possibly spend 55 minutes on the elliptical machine without “lots of things to do.” This includes relentless无情，不懈 channel surfing.

“I switch constantly,” she said. “I can’t stand commercials. I have to flip around unless I’m watching ‘Project Runway’ or something I’m really into.”

Some researchers say that whatever downside there is to not resting the brain, it pales in comparison to the benefits technology can bring in motivating people to sweat.

“Exercise needs to be part of our lives in the sedentary坐 world we’re immersed in. Anything that helps us move is beneficial,” said John J. Ratey, associate clinical professor of psychiatry at the Harvard Medical School and author of “Spark: The Revolutionary New Science of Exercise and the Brain.”

But all things being equal, Mr. Ratey said, he would prefer to see people do their workouts away from their devices: “There is more bang for your buck doing it outside, for your mood and working memory.”

Of the 70 cardio machines on the main floor at Bakar Fitness, 67 have televisions attached. Most of them also have iPod docks and displays showing workout performance, and a few have games, like a rope-climbing machine that shows an animated character climbing the rope while the live human does so too.

A few months ago, the cable TV went out and some patrons were apoplectic激动. “It was an uproar. People said: ‘That’s what we’re paying for,’ ” said Leeane Jensen, 28, the fitness manager.

忙里偷闲，什么是闲

At least one exerciser has a different take. Two stories up from the main floor, Peter Colley, 23, churns away on one of the several dozen elliptical machines without a TV. Instead, they are bathed in sunlight, looking out onto the pool and palm trees.

“I look at the wind on the trees. I watch the swimmers go back and forth,” Mr. Colley said. “I usually come here to clear my head.”

动亦难，静亦难

朱熹说，心体本身运动不息。

人要静下来，比什么都难。

佛教和气功的入定，太难了。

红楼梦里的妙玉不是因为入定而走火入魔吗？