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Athletes can suffer from various degrees of overtraining. NFOR is non-functional overtraining, and OTS is overtraining syndrome. The symptoms are similar, but you can recover from NFOR in a few weeks or months, while the recovery period for OTS can be years and an athlete will most likely never reach their best level again. So it is important to make the correct diagnosis of NFOR and OTS quickly. The Human Physiology (MFYS) research group of the Vrije Universiteit Brussel collected data from 100 athletes and developed a unique test to determine the difference: the TOP test, or training optimisation test. This is the only scientific test to differentiate between NFOR and OTS. The results of the research by Professor Romain Meeusen’s team were published in the leading journal Medicine & Science in Sports & Exercise.


To improve their performance, athletes often step up their training. A certain degree of overload combined with sufficient recovery time leads to performance improvement. This is called functional overreaching or functional overtraining. When the balance between training and recovery is not right, non-functional overstraining (NFOR) can occur. The first symptoms of NFOR are a decline in performance, persistent fatigue and reduced mental resilience. Failure to recognise NFOR in time can result in overtraining syndrome (OTS).


The difference between NFOR and OTS is difficult to determine. They have similar characteristics such as decreasing performance, high levels of fatigue and psychological and hormonal disturbances, symptoms that can also be present when an athlete is ill.


Professor Meeusen’s team therefore always starts by excluding all other possible causes of the drop in performance. During a thorough medical check-up they look for organic diseases or infections and examine the athlete’s blood and their hormonal state. The psychomotor abilities are tested, with a number of attention and reaction time tests, and psychological questionnaires are used to examine the athlete’s state of mind. After other possible causes have been excluded, it is a question of determining whether the athlete is suffering from NFOR or OTS.


For this purpose, the TOP test is used. For the TOP test, two exercise tests are performed in which hormone values (ACTH, Growth Hormone and Prolactin) are measured. The hormones come from the pituitary gland and are good indicators for the body’s ‘stress state’.  Between the two tests there is a break of about four hours. The reaction of the hormones to the second test is important. If the reaction rises sharply compared to the first test, one can assume NFOR. In an athlete with OTS, the pituitary gland will not react to the second test. “We assume that in OTS various biological, neurochemical and hormonal regulatory mechanisms no longer function properly,” says Professor Meeusen. “If there is little or no reaction from the hormones, we can assume that the athlete has overtraining syndrome. We developed this TOP test after it was established in many cases that athletes who train twice a day often perform worse during afternoon training. With this test we can now identify a case of NFOR in time and take action. Even better of course is prevention. We have also designed a questionnaire that trainers can use.”