LONDON, ENGLAND: We have all seen them on the train or the bus. Chins glued to their chests, thumbs hovering and their eyes locked in a digitally induced trance.

But according to a report on CNN.com, a British occupational psychologist is arguing that persistent monitoring of one's BlackBerry will increase stress levels and most likely decrease productivity too.

CNN.com said that Mr Amir Khaki from AK Consulting had studied the BlackBerry habits of a group of executives in middle to senior management who were either high or low frequency users.

'High' users typically switch on their BlackBerrys during the commute to work and keep them on in the evenings and during weekends.

'Low' users generally allocate specific times to check their BlackBerrys and respond to e-mail.

'People who fell into the high user category tend to have a distorted perception of their own usage and they equate their BlackBerry use with being dedicated to the job,' Mr Khaki said.

But these displays of enthusiasm did not translate into efficiency. In one example, Mr Khaki observed a high frequency user trying to complete a simple spreadsheet. The task, Mr Khaki estimates, should have taken about 20 minutes but ended up taking three times as long because of BlackBerry monitoring.

The knock-on effect of this disruption is the anxiety it creates.

'You're not finishing what you are supposed to be doing. The dependency it creates when you can't find it, or its buzz when you can't do anything about it because you are in a meeting, causes stress,' he said.

While high users are driven to distraction, their partners are sometimes compelled to destruction.

'Many hated them. I heard a story of one being flushed down the toilet,' Mr Khaki said.

He advises companies whose employees have been issued with a smartphone to at least provide a basic level of training.

'You need to know how to use it properly. After all, we get training when every other technology comes online,' Mr Khaki said.

He suggests companies try to encourage their employees to set a limit on usage. Of course, there are going to be exceptions but, on the whole, he recommends a maximum of 12 hours of use during the working week.

On a personal level, his advice is simple: 'At the start of any task, turn it off! Interruptions don't help anyone do anything better, faster or at a higher quality.'

He added that research suggests people who respond to e-mail in batches take much less time doing it and are better at it.

With more people upgrading to smartphones, issues over productivity and stress will surely rise as more executives find the line between work and leisure time blurring.

It is a trend which concerns organisational psychology and health professor Cary Cooper, from the Lancaster University Management School in Britain.

'We are finding that people are working on their paid work in what used to be their leisure time and that's having consequences both for their health and their productivity,' Prof Cooper told CNN.

He believes the recession has perhaps compounded the problem as people feel more insecure about their jobs but he advises people: 'Use your BlackBerry rationally. If you are on holiday, access it once every two days, explain to someone that you are away and you'll deal with it when you get back.

This article was first published in The Straits Times.