“…The studies varied in many respects, as exercise duration (short time-from 1 to 8 days, long-lasting-from 2 to 12 months), exercise type, exercise intensity (moderate, moderate-to-vigorous, acute until exhaustion), training conditions (hypoxic, normoxic conditions, indoor training, outdoor training), sex, and measuring the timing of maximal secretion of MT as well as the measurement methods. An increase of MT concentration following PE in the morning [ 90 ] and in hypoxic conditions [ 91 ], decreases in the same [ 79 , 92 ], and a lack of the effect [ 93 , 94 ] were reported. Referring to the MT measurement timing, Carlson et al [ 90 ] observed that exercise performed in the morning resulted in elevated MT secretion by 20% compared to the hormone secretion induced by the afternoon exercise.…”