London: If you think a weekend lie-in can help compensate for your week's sleep loss, think again – it doesn't make up for the hours of shut-eye lost, scientists have claimed.

Researchers at the Penn State College of Medicine in Pennsylvania found that performance deteriorates when sleep is regularly restricted to six hours per night -- and does not improve after two nights of "recovery" sleep.

While having a lie-in helps people feel a bit more clear-headed, they are still slow and clumsy, a news daily reported.

For the study, the researchers monitored young men and women who spent 13 consecutive nights in a sleep lab.

They slept eight hours per night for the first four nights. After that, their sleep was restricted to six hours per night for six nights, followed by three "recovery nights" of ten hours' sleep.

Lead researcher Dr Alexandros Vgontzas said: "After one work week of mild sleep deprivation, two recovery nights were adequate in improving sleepiness but not performance.

"The usual practice of extending sleep during the weekend after a busy work week associated with mild sleep loss is not adequate in reversing the cumulative effects on
cognitive function resulting from this mild sleep deprivation."

But there is some good news -- at least for men who find it hard to get out of bed at the weekend.

The research shows that they are less able to cope with lack of sleep than the fairer sex -- meaning that if anyone deserves a late start in the morning, they do.