In each of our days, we all experience those more positive moments, in which we feel productive, positive, active. These “highs” do, however, have their opposite moments. These “lows” can often be attributed to mental fatigue, which in turn leads to a reduction in cognitive performance. It is common knowledge that a tired individual will not perform as efficiently or as effectively. In these scenarios, errors can occur.

Each day, our body experiences two different rhythms: circadian and zeitgeber. While the first controls our natural body clock, the second regulates body temperature, mental performance and sleep. When one experiences jet lag, or when working shifts, these rhythms can be out of sync and this can have an adverse effect on the body in the form of fatigue and lethargy.

What may, however, be a revelation, is the fact that there are times of the day when individuals are more prone to mental fatigue. Specifically, at 3am and 3pm, an individual will naturally experience lows that make one more error-prone. Common symptoms include tiredness, a drop in energy levels or even feelings of exhaustion. At 3am, if we are still awake, our body needs sleep. It will shows us this need through the common signs of fatigue. This happens at 3pm as well: the time at which our body naturally requires a siesta. Studies have shown that the margin of error in workplaces is larger at these two key moments than at any other time of the day.

Distribution of more than 75,000 gas meter-reading errors across the 24-h period. Redrawn from Bjerner et all. 1995

Understanding these rhythms and their importance for our body and our health is fundamental to decrease the risk of error. Scheduling breaks for these more risk-prone moments and resting can not only see us through them but also improve our overall performance. This will not only make us happier and healthier but also save us and our organizations time and money.
In the specific scenario of jet lag, mental fatigue occurs when the body tries to resync its rhythms to adapt to the new time zone. It is due to the effort of resynchronising to the local daylight-darkness cycle. Symptoms are similar for shift workers, with ever changing work patterns.

It is important to note that the negative effects of mental fatigue are at their peak before dawn and during mid-afternoon.
Taking a nap, resting, spending some time away from the computer screen and scheduling breaks during these ‘rough’ periods can help fight the symptoms of fatigue. Understanding and respecting these rhythms is thus certainly advantageous in the long term.
If you are interested in learning more on how to fight fatigue do consider this book: "21 Tips For Beating Fatigue And Improving Your Health, Happiness And Safety"