Purpose The aim of this study was to examine how intensifying training loads over a week affects the sleep patterns of young soccer players on the nights immediately following the intensified training sessions. Methods Quasi-experimental study. Fifteen young athletes participants of a team engaged in national level competition, underwent two weeks of training with varying load magnitudes—Week 1: low accumulated training load and Week 2: intensified training loads [40% increase in external training load(ETL)]. To characterize the intensification of the workload, the methods PlayerLoad and RPE-Session were employed to measure ETL and internal training load(ITL), respectively. Total sleep time(TST), total time in bed(TTB), sleep efficiency(SE), sleep latency(SL), and wake after sleep onset(WASO) were obtained using actigraphy and daily sleep log. The variables were compared among the days of week (e.g. Monday of week 1 with Monday of week 2, and so forth). Results Acute training intensification in week 2 led to significant increases in ETL and ITL on Monday and on Wednesday(p < .05), and ETL(p < .05) on Friday on the second week. Improvements in sleep were observed (Tuesday—TST:+80 min, WASO:-29.3 min, SL:-8 min, SE:+9%; Thursday—TST:+86 min, SL:-4 min, SE:+4%; Saturday—TST:+40 min, SL:+1 min) compared to the same day of the previous week. Correlations between ETL and ITL(r = 0.637), ITL and TST(r = 0.572), ITL and SE(r = 0.548) were found. Conclusion Intensification of training loads results in alterations in sleep variables, notably an elevated TST and SE in the days subsequent to the acute load increment.
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