The balance between recovery and stress and between training and rest is of high importance in the daily routine of competitive athletes, and is a substantial component for optimal competition preparation (Hausswirth & Mujika, 2013; Kellmann & Beckmann, 2018a). Fast and effective regeneration and recovery have become important due to the increased frequency of competition, which is related to social and media pressures and the constant pursuit for performance improvement. The greater demand on athletes is supported by literature findings of inadequate recovery phases and overload symptoms in athletes from different sport disciplines (Dupont et al., 2010; Ekstrand, Walden, & Hagglund, 2004; Main & Landers, 2012; Meyer, 2010). Increased training stimuli for a long period combined with insufficient recovery can lead to a performance stagnation or decrease and may even involve a chronic maladaptation. This is known as overtraining syndrome (Meeusen et al., 2013; Meeusen & De Pauw, 2018). Progressive fatigue and underperformance can be the result of a long-term underrecovery (Halson, 2014; Kellmann & Beckmann, 2018a). However, the difficulty is to determine the exact point when conventional training turns from overreaching into non-functional overreaching.