Melatonin Secretion and Impacts of Training and Match Schedules on Sleep Quality, Recovery, and Circadian Rhythms in Young Professional Football Players Almendros-Ruiz, Antonio Conde Pipó, Javier Aranda Martínez, Paula Olivares Jabalera, Jesús Acuña-Castroviejo, Darío Requena, Bernardo Fernández Martínez, José Mariscal Arcas, Miguel Circadian rhythm melatonin Training time Football performance Sleep This study was funded by the High Council for Sports (CSD), the Spanish Ministry of Culture and Sport, through the NESA NETWORK Spanish Network of Sports Care at Altitude Ref. 19/UPB/23. This work has been carried out with the support of the University of Granada PPJIB2021-22. Modern elite football is becoming increasingly physically demanding, often requiring training and matches to be played at night. This schedule may disrupt circadian rhythms and melatonin secretion, thereby impairing sleep and recovery. This study investigated the effects of training time on melatonin secretion, circadian phase markers, and sleep parameters in elite youth soccer players. Forty male players (aged 16–18 years) from an elite Spanish youth football club were studied. Two groups followed the same training program but trained either in the morning (MT) or in the evening (ET). Salivary melatonin was measured at six time points to determine the mean levels, dim light melatonin onset (DLMO), amplitude, and acrophase. Chronotype, sleep quality (PSQI), and daytime sleepiness (ESS) were assessed using validated questionnaires. Dietary intake and anthropometric variables were also recorded. The MT group had higher mean melatonin levels (p = 0.026) and earlier DLMO (p = 0.023) compared to the ET group. Sleep quality was significantly better in the MT group (p < 0.001), despite shorter sleep duration (p = 0.014). No major differences in diet or anthropometry were observed. The chronotype had a secondary effect on the circadian markers. Evening training is associated with alterations in melatonin rhythms and reduced sleep quality, possibly due to light-induced chronodisruption. These findings highlight the importance of training timing as a modifiable factor in the chronobiology and recovery of athletes. Incorporating circadian principles into training schedules may optimize resting time and thus performance and long-term health in athletes. 2025-07-02T08:17:06Z 2025-07-02T08:17:06Z 2025-05-11 journal article Almendros-Ruiz A, Conde-Pipó J, Aranda-Martínez P, Olivares-Jabalera J, Acuña-Castroviejo D, Requena B, Fernández-Martínez J, Mariscal-Arcas M. Melatonin Secretion and Impacts of Training and Match Schedules on Sleep Quality, Recovery, and Circadian Rhythms in Young Professional Football Players. Biomolecules. 2025; 15(5):700. [DOI: 10.3390/biom15050700] https://hdl.handle.net/10481/105030 10.3390/biom15050700 eng http://creativecommons.org/licenses/by/4.0/ open access Atribución 4.0 Internacional MDPI