According to a survey of participants published on Wednesday, most of the companies had seen no loss of productivity during the experiment, and some had seen a significant improvement.

Thirty-five of the 41 companies that responded to a survey said they were likely or extremely likely to keep the four-day workweek after the trial is over. Most of the companies said productivity was the same or better. Six companies said productivity had gone up.

The idea of a four-day workweek has been around for a long time. It has not materialized on a large scale, but Vice President Richard M. Nixon predicted it in the not too distant future. Changes in the workplace over the coronaviruses have given rise to questions about other parts of work. Is working five days a week just because we have done it for a long time, or is it really the best way to work?

Joe O'Connor is the chief executive of 4 Day Week Global, a nonprofit group that is conducting the study with a think tank and researchers at Cambridge University. Many benefits can be brought by remote and hybrid work, but it doesn't address overwork.

The four-day week gave employees more time to exercise, cook, spend time with their families and take up hobbies, according to some leaders of companies in the trial. Critics were concerned about the added costs and reduced competitiveness of European companies.

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More than 3,300 workers in banks, marketing, health care, financial services, retail, and other industries in Britain are taking part in the pilot, which is one of the largest studies to date.

Mark Roderick, the managing director and co-owner of Allcap, said it was too early to say how the shortened workweek had affected productivity or the company's bottom line. Employees were happy with the extra day off and the company was considering continuing it.

The company's headquarters are in Gloucester, England.

The new schedule gave Mr. Roderick more time to prepare for the triathlon. Since summer holidays and the shorter workweek have meant that staff can be stretched thin, some days are more stress than they might have been. He used a British phrase for "in a difficult situation."

Experiments similar to the one conducted in Britain are being done in other countries as well. Employees in a trial completed the same amount of work.

The four-day workweek at Amplitude Media was such a success that the company hopes to make it permanent, according to the managing director. She said that employees have found ways to work better. Even though half of the employees are off on Wednesday and Friday, the company is still growing and delivering the same amount of work.

It has made me not ping from thing to thing all the time. She is a painter and feels calmer. She said that the real test will be how the experiment goes over the final few months as the company grows.

The founder and chief executive of 5 Squirrels, a skin care manufacturer based in England, said that employees had become more productive, while making fewer errors, and that they were collaborating better.

He said that they have gotten away from that because they are all trying to get out of here at five o'clock.