From The Ergoweb® Learning Center

Study Quantifies Sleep Deprivation Effects

Fatigue and confusion significantly occurred among research subjects following one night of sleep deprivation (SD – total lack of sleep) and did not return to a baseline level after a one night (seven-hour) sleep opportunity ,according to a recently published Japanese study involving 10 healthy young males. One night of SD also affected high-order cognitive capabilities such that a return to baseline scores took at least two nights of sleep opportunity.

One night of SD induced subjective sleepiness recovered to a baseline value following one night of sleep.

SD did not seem to impact tasks involving simple addition and simple word memory.

The Bottom Line – How This Applies To Ergonomists

There are many factors that affect the quantity of sleep workers obtain.  In the work setting, key issues include:

  • psychosocial risk factors
  • company hours-of-work policy
  • symptoms related to an injury or chronic condition

This study shows that one night of SD significantly impacts the level of employee fatigue and confusion.  Further, one night of SD leads to a poor performance of high-order cognitive tasks and requires two nights of sleep to return to normal capability.

Although the affects of sleep loss may seem obvious, this study quantifies the impact of SD to show how it can affect the decision making of employees at any level within a company and ultimately, the business profit margin.

Other Key Study Points

Regardless of test day, the mean score for sleepiness was significantly higher at 8:00 am compared to 8:00 pm for all sleepiness scales.

The mean score of depression-dejection mood was significantly lower at 8:00 am than at 8:00 pm.

Tension-Anxiety mood score was lower on the 1st and 2nd recovery days compared to baseline.

Study Method

The study subjects were 10 healthy men between 19 and 25 years of age. The volunteers’ normal daily sleep duration ranged from six to eight hours.

Day One (Baseline)
Following a 7-hour night of sleep, subjects reported to the laboratory for evaluation of:

  • mood Profile of Mood States)
  • sleepiness Kwanseigakuinn Sleepiness Scales, Stanford Sleepiness Scale and Visual Analogue Scale)
  • task performance (Simple addition task, paced auditory serial addition task, simple words memory task, reading span test, continuous performance task, and Wisconsin card sorting test) Prior to the investigation, volunteers reviewed and practiced the tasks

Volunteers then performed their normal daily activities. Twelve hours later, subjects returned to the lab and completed the same questionnaires and tasks. That evening, the volunteers were not allowed to sleep.

Day Two
At 8:00 am and 8:00 pm, the same questionnaires and tasks were performed.  Otherwise, subjects performed their normal daily activities.  At 11:30 pm, the volunteers were allowed to rest (this meant participants completed 41 hours of total wakefulness) for seven hours.

Days Three, Four, and Five
Subjects woke up at 6:30 am.  At 8:00 am and 8:00 pm, the same questionnaires and tasks were performed.  Subjects performed their normal daily activities, went to bed at 11:30 pm, and were allowed seven hours of rest.

Subjects received a base fee and a “performance bonus” to motivate high productivity.  Although participants did not know the bonus criteria, benchmarks were set such that all subjects received the bonus if tasks were completed with a demonstration of effort. 

This complete paper can be viewed without fees at:

Article Title: Recovery of cognitive Performance and Fatigue after One Night of Sleep Deprivation

Publication: Journal of Occupational Health, 51:412-422, 2009

Authors: K Ikegami, S Ogyu, Y Arakomo, K Suzuki, K Mafume, H Hiro, and S Nagata

This article originally appeared in The Ergonomics Report™ on 2009-12-28.