The human body is capable of adapting to complicated situations: physical or intellectual effort, illness... But beyond a certain threshold, the burden becomes too heavy. Fatigue is an alarm signal that we must know how to listen to. This is not always easy in a world as demanding as ours, where we must constantly be at the top, improve our performance and prove our abilities.  

Fatigue: when should you worry?

Legs like lead, difficulty getting up in the morning? Fatigue can have multiple causes that are not always easy to understand. If it persists for more than 15 days, it is better to consult a doctor because it may reveal an underlying pathology.

However, many people do not dare to talk about it. "Often, fatigue is not accepted. Some people are afraid of being seen as a slacker. It is not always well recognized by patients and doctors," says Dr. Grégoire Cozon, immunologist at the Lyon University Hospital and author of Stop à la fatigue (Dunod, 16.90 €).

Another difficulty: fatigue is difficult to evaluate, as it can be felt differently from one person to another. "We have not yet invented the fatigometer," observes Dr. Cozon, who emphasizes that each individual has his or her own "fatigue threshold" that should not be exceeded.

If you have the impression that you are no longer able to accomplish your usual tasks with the same speed and efficiency as before, it is time to ask yourself the right questions. 

Physical fatigue: take the staircase test

Physical fatigue is stronger at the end of the day. Typically, we are "full of it". This weariness can be the consequence of an intense physical effort and manifest itself by aches and pains or cramps. But it can also result from a viral infection (Covid, infectious mononucleosis, flu...), an inflammatory, cardiac or pulmonary disease or an endocrine imbalance (hypo or hyperthyroidism, for example). In all cases, it is the treatment of the disease that will help overcome this fatigue.

In women who have heavy periods and people who suffer from digestive microbleeding, blood loss can lead to iron deficiency over time, the main symptom of which is fatigue. This anemia can be treated by taking iron tablets, preferably under medical supervision.

How do you know if you have exceeded your physical capacity?

The staircase test can help you decide. A healthy adult should recover within five minutes after walking up six flights of stairs. But if the shortness of breath persists, if it is difficult to get going again and if you feel more or less irritated, then this fatigue is not normal. Lack of training or real pathology? Only a medical check-up can give the right answer.

Mental fatigue: overwork or depression?

Mental fatigue is typically felt in the morning upon waking up and persists throughout the day. The brain turns in slow motion with, as a consequence, difficulties to concentrate, to fix its attention and to memorize. This fatigue can go as far as apathy, all motivation having disappeared.

Most of the time, it is the result of overwork (for example, for a student during an exam period) or a lack of sleep.

To get out of it, it is absolutely necessary to put your brain at rest even if, very often, it is easier to say than to do... In concrete terms, you will have to slow down your activities, take breaks and, above all, avoid ruminating and feeling guilty, otherwise you will exhaust all your energy reserves and fall into burnout.

Before that happens, activities such as yoga, tai chi, qi gong or meditation, which focus attention on breathing and movement, can provide a certain amount of relief.

To recover from a sleep debt, it is sometimes enough to slightly modify one's lifestyle (going to bed and getting up at the same time, sleeping in a cool room, avoiding exposure to blue light from screens at night...) to get back into shape.

However, one should not neglect episodes of sleepiness during the day. These untimely falls asleep can reveal a sleep apnea syndrome. If left untreated, this disease can have serious cardiac consequences. Once again, it is important to talk to your doctor, especially if you snore and stop breathing during the night.

Mental fatigue can also affect patients after Covid, often associated with intense and persistent physical fatigue. Patients, even when recovered, frequently complain of a feeling of "mental fog" with difficulties in concentration and sleep disturbances that sometimes require psychological support.

Finally, if this mental fatigue is accompanied by dark thoughts, sadness and an inability to perform daily tasks, the problem must be taken seriously because it may be a depression. Medical advice is required.

Fatigue: when to consult?

Most of the time, fatigue is only temporary. Everything goes back to normal after a good night's sleep or a few days off. But "if the fatigue does not subside after a weekend of rest and lasts more than 15 days without any particular cause, you should consult a doctor", says Dr Cozon. Only a professional can identify the real cause of this exhaustion and propose an effective treatment.

In rarer cases, the fatigue persists for several months. For the specialist, it is necessary to consider a chronic fatigue syndrome (CFS) beyond six months of unexplained exhaustion in adults, three months in children. This disease affects between 300 000 and 600 000 people in France. In the most serious cases, even a minimal physical or intellectual effort can cause a real malaise. "These patients may take several days or weeks to recover from what they call a crash," Dr. Cozon points out. The diagnosis of CFS is complex and requires the advice of a specialist. The French Chronic Fatigue Syndrome Association offers support and practical advice to those affected. Fatigue is not a fatality!