It also found their mood was better on gym days than non-gym days.The study has been published in the International Journal of Workplace Health Management

The study found that exercise re-energised staff, improved their concentration and problem solving and made them feel calmer.Experts said the findings should encourage more businesses to provide facilities for staff to exercise.

They also felt they might be criticised by colleagues for taking time out from their desk jobs, the study found, reports the Telegraph.In the study, the volunteers were asked to fill out short questionnaires about their mood and work productivity on two working days of their choice - one set for a day they decided to exercise and a second set for another day.

Lead author Jo Coulson, from Bristol University, said: "It's generally well-known now that there are many physical and mental health benefits that can be gained from regular exercise.

"If people try to fit an active break into their working day, they might also experience the added bonus of their whole day feeling much more productive. And that always feels good in our busy lives.

"The study also begs the question whether employers can afford not to be encouraging active breaks."The suggestion is that employers who are ahead of the game in offering proper onsite facilities actually get less from their employees on days that they don't exercise."