Functional overreaching (FOR) occurs after well-timed periods of relatively large training loads and adequate restoration. Athletes suffering from NFOR/overtraining syndrome (OTS) might not present with ‘textbook symptoms’; instead, they could be asymptomatic, display a myriad of individualised symptoms or exhibit normal symptoms of acute fatigue. The protocol involves two graded exercise tests to exhaustion with a 4-h rest between bouts and involves measures of adrenocorticotropic hormone (ACTH) and prolactin (PRL), measured at four time points: baseline, immediately after completion of the first test, prior to the second test and immediately after the second test. An important feature of NFOR/OTS is the inability to sustain exercise performance, and several studies have indicated NFOR using simulated or sport-specific performance testing such as incremental testing, time to exhaustion and competition performance. Disturbances in mood state are often reported in athletes suffering OTS and appear to be sensitive to periods of intensified training in both endurance and strength sports.