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Phys Ed Gretchen Reynolds on the science of fitness.

To combat afternoon slumps in enthusiasm and focus, take a walk during the lunch hour.

A new study finds that even gentle lunchtime strolls can perceptibly — and immediately — buoy people’s moods and ability to handle stress at work.

It is not news, of course, that walking is healthy and that people who walk or otherwise exercise regularly tend to be more calm, alert and happy than people who are inactive.

But many past studies of the effects of walking and other exercise on mood have focused on somewhat long-term, gradual outcomes, looking at how weeks or months of exercise change people emotionally.

Fewer studies have examined more-abrupt, day-to-day and even hour-by-hour changes in people’s moods, depending on whether they exercise, and even fewer have focused on these effects while people are at work, even though most of us spend a majority of our waking hours in an office.

So, for the new study, which was published in the Scandinavian Journal of Medicine and Science in Sports this month, researchers at the University of Birmingham and other universities began by recruiting sedentary office workers at the university.

Potential volunteers were told that they would need to be available to walk for 30 minutes during their usual lunch hour three times a week.

Most of the resulting 56 volunteers were middle-aged women. It can be difficult to attract men to join walking programs, said Cecilie Thogersen-Ntoumani, the study’s lead author and now a professor of exercise science at Curtin University in Perth, Australia. Walking may not strike some men as strenuous enough to bother with, she said. But she and her colleagues did attract four sedentary middle-aged men to the experiment.

The volunteers completed a series of baseline health and fitness and mood tests at the outset of the experiment, revealing that they all were out of shape but otherwise generally healthy physically and emotionally.

Dr. Thogersen-Ntoumani and her colleagues then randomly divided the volunteers into two groups, one of which was to begin a simple, 10-week walking program right away, while the other group would wait and start their walking program 10 weeks later, serving, in the meantime, as a control group.

To allow them to assess people’s moods, the scientists helped their volunteers to set up a specialized app on their phones that included a list of questions about their emotions. The questions were designed to measure the volunteers’ feelings, at that moment, about stress, tension, enthusiasm, workload, motivation, physical fatigue and other issues related to how they were feeling about life and work at that immediate time.

A common problem with studies of the effect of exercise on mood, Dr. Thogersen-Ntoumani said, is that they rely on recall. People are asked to remember hours or days after the fact how exercise made them feel. Given how fleeting and mysterious our emotions can be, recalled responses are notoriously unreliable, Dr. Thogersen-Ntoumani said.

Instead, she and her colleagues wanted in-the-moment assessments from people of how they felt before and after exercise. The phone app questions provided that experience, she said, in a relatively convenient form.

Then the first group began walking. Each volunteer was allowed to walk during one of several lunchtime sessions, all of them organized by a group leader and self-paced. Slower walkers could go together, with faster ones striding ahead. There was no formal prescribed distance or intensity for the walks. The only parameter was that they last for 30 minutes, which the volunteers had said would still allow them time to eat lunch.

The groups met and walked three times a week.

Each workday morning and afternoon during the first 10 weeks, the volunteers in both groups answered questions on their phones about their moods at that particular moment.

After 10 weeks, the second group began their walking program. The first group was allowed to continue walking or not as they chose. (Many did keep up their lunchtime walks.)

Then the scientists compared all of the responses, both between groups and within each individual person. In other words, they checked to see whether the group that had walked answered questions differently in the afternoon than the group that had not, and also whether individual volunteers answered questions differently on the afternoons when they had walked compared with when they had not.

The responses, as it turned out, were substantially different when people had walked. On the afternoons after a lunchtime stroll, walkers said they felt considerably more enthusiastic, less tense, and generally more relaxed and able to cope than on afternoons when they hadn’t walked and even compared with their own moods from a morning before a walk.

Although the authors did not directly measure workplace productivity in their study, “there is now quite strong research evidence that feeling more positive and enthusiastic at work is very important to productivity,” Dr. Thogersen-Ntoumani said. “So we would expect that people who walked at lunchtime would be more productive.”

As a pleasant, additional outcome, all of the volunteers showed gains in their aerobic fitness and other measures of health at the completion of their 10 weeks of walking.

But, tellingly, many said that they anticipated being unable to continue walking after the experiment ended and a few (not counted in the final tally of volunteers) had had to drop out midway through the program. The primary impediment to their walking, Dr. Thogersen-Ntoumani said, had been “that they were expected by management to work through lunch,” suggesting that management might wish to acquaint themselves with the latest science.

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