BAKERSFIELD, Calif. -- Humans spend about one-third of their lives asleep, so it's no wonder that people often try to cheat the system by rising early and going to bed late.

Many people think they can make up a sleep debt with one or two good nights of rest on the weekend, but new research from Brigham and Women's Hospital has suggested this is impossible.

Scientists studied healthy volunteers in a sleep lab for three weeks. The participants kept a schedule that was similar to an on-call doctor -- 33 hours awake, followed by 10 hours of sleep.

On average, this translates to less than 6 hours of sleep per night.

They found that volunteers' reaction times improved after they had a chance to sleep -- but this improvement steadily wore off over the course of the day.

In the late hours, people's chronic sleep loss caught up with them and caused them to make more errors.

Researchers said the resulting sleep debt creates a dangerous situation for late-night drivers or those who work overnights in a hospital.