Background: Training program and distribution of training load may influence sleep characteristics. Aim: The aim of the study was to examine sleep characteristics, hormonal and immunological responses of young swimmers in microcycles of training after a redistribution of the training load. Methods: Twelve swimmers, recorded their sleep during one week of low-load training (BS). The following two consecutive weeks they performed in a counterbalanced cross-over design two training conditions: i) one week including 8 training sessions (2 morning and 6 afternoon: EXP) and ii) one week including 6 training sessions (evening only: CON) and a total training load equal to EXP. Training load was calculated by the product of the rating of perceived exertion (RPE) and the training duration. Time in bed (TIB), time out bed (TOB), total sleep time (TST), time from lying down to sleep onset (SOL), sleep efficiency [SE:(TST/TBT)*100] and minutes awake after sleep onset (WASO) were recorded with actigraph. On days of morning training in EXP and the corresponding days and times in CON (Tuesday and Thursday) a saliva sample was taken before and after the afternoon training to determine cortisol and immunoglobulin A concentration. Results: Training load was not different between EXP and CON (p=0.31). TBT, TST and TOB were decreased during EXP condition compared to CON (5±24, 5±15 and 11±12%, respectively, p<0.01) and BS (10±12, 11±24 and 13±38% respectively, p<0.01) without any difference in SE (p=0.33). Cortisol concentration did not differ between conditions (p=0.08) but was 98% higher at start compared to the end of training in both conditions (p<0.01). Immunoglobulin A concentration was not different between conditions (p=0.43) but was 50% lower post-training on Thursday compared to pre-training on Tuesday in both conditions. Conclusions: Inclusion of two morning training sessions reduces the quantitative sleep characteristics but does not affect its quality. A moderate reduction does not affect hormonal and immune function during the microcycle.
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