Sleep in German female youth national ice hockey athletes

Descriptive statistics, which are presented in Table 1, showed that the mean PSQI global score at T1 exceeded the corresponding score at T2, indicating a reduction from the first to the second measurement. Paired t-test results indicated a significant change in PSQI global scores from pre- to post-TC assessments (t = 2.33, p = 0.031, df = 19), with a medium effect size (d = 0.52). The test–retest reliability of PSQI scores, however, was rather small, with a moderate correlation (r_s = 0.471, p = 0.036). Descriptively, the division into categories dividing good from poor sleepers on the basis of the PSQI global score indicated a change from pre- to post-TC measurements, as can be seen from Fig. 1. At T1, 50% of players were identified as good sleepers, while 45% were categorized as poor sleepers and 5% were categorized as showing very poor sleep quality (PSQI scores > 10). The proportion of good sleepers increased at T2, with 65% categorized as good sleepers and 35% identified as having poor sleep quality.

Focusing on the PSQI component scores for ’subjective sleep quality,’ paired t-test results indicated no significant change from T1 (1.05 ± 0.51) to T2 (1.10 ± 0.64; t = −0.57, p = 0.577, df = 19), and the effect size was trivial (d = 0.13). Regarding the component scores for ’sleep duration,’ there was a significant difference between T1 (0.30 ± 0.57) and T2 (0.00 ± 0.00; t = 2.35, p = 0.030, df = 19), with a medium effect size (d = 0.53).

Regarding the descriptive statistics in Table 1, the ESS global score before TC was slightly higher than the post-TC ESS mean score. Regarding ESS global scores, results of the paired t-test indicated no significant pre- to post-TC difference (t = 0.67, p = 0.510, df = 19), and the effect size was trivial (d = 0.15). The test–retest reliability of ESS scores was nearly acceptable, with a moderate correlation (r_s = 0.647, p = 0.002). As can be seen from Fig. 2, at T1, ESS scores were in a normal range of daytime sleepiness for 65% of players, while the remaining 35% showed excessive daytime sleepiness (ESS scores > 10). At T2, 75% showed normal daytime sleepiness, while 25% exceeded a score of 10 and were thus categorized as exhibiting excessive daytime sleepiness.

As can be seen from Table 2, descriptive data differed between the OG and DG. At both measurements, T1 and T2, the mean PSQI score of F was higher than the corresponding score of D and G. Concerning the ESS, a different pattern emerged: while the ESS score of F slightly exceeded the DG score at T1, at T2, in contrast, the score was lower in the OG compared to the DG. When divided by position, no intergroup differences were found, neither for the PSQI and ESS global scores at T1 and T2 nor for their difference scores depicting changes over time, as Mann–Whitney U test results were not statistically significant (p > 0.1).

The aim of this study was to assess subjective sleep quality and daytime sleepiness in German female youth national ice hockey athletes at the start and end of a TC immediately preceding the World Championship Division IA tournament. Results imply a significant increase in subjectively perceived sleep quality over the course of the TC. Based on the results of the component score analyses, this increase appears to be due to increased sleep duration over the course of the TC rather than due to an increase in subjective sleep quality. There was no statistically significant trend for the sample’s daytime sleepiness. Descriptively, there was a reduction in daytime sleepiness from the start of the TC to the end. Thus, a pre-tournament TC seems to be an effective and beneficial measure to ensure an improvement in sleep quality and decline of sleepiness, as a prerequisite for performance readiness in an upcoming tournament. The reduction in training intensity during the TC and the temporary reduction of the double burden of school and training due to the Christmas holiday period might have been major influencing factors in this improvement of sleep quality and daytime sleepiness [25]. The implementation of guided relaxation techniques before bedtime, the absence of smartphone use before going to sleep, and scheduled bedtimes, which all constitute sleep hygiene interventions [10], probably promoted more restful sleep. Anecdotal reports from athletes indicated a beneficial effect of relaxation techniques, which should be systematically assessed in future studies on the effects of sleep hygiene interventions. TC conditions of short distances between the hotel and ice stadium, having meals together, and the common bedtime routine potentially promoted stress reduction and (social) recovery, which, in turn, positively affected sleep and sleepiness [17, 22]. For some athletes the opposite trend was observed, as they showed an increase in daytime sleepiness or a decrease in sleep quality from pre- to post-TC measurements. The unfamiliar sleep environment of the hotel, the fact of sharing bedrooms with a teammate, and different sleeping conditions might have interfered with sleep in these players more than for others [18], and/or they may be more sensitive or already slightly disturbed sleepers. Performance pressure and nervousness due to the nomination process and the upcoming tournament constitute other possible factors that might have contributed to the impairment of sleep quality and daytime sleepiness in some players. These individual deviations from the average trend in the team underline the individuality of sleep and sleeping behavior, requiring an individual assessment and evaluation of sleep [14, 30].

Comparison with other studies that examined sleep in athletes shows that the average PSQI and ESS scores of the sample were quite similar to those reported in previous studies on male and female winter Canadian national team athletes, highly trained team sport athletes, and collegiate student athletes (e.g., female student athletes, female field hockey players) [4, 21, 29]. The sample’s mean scores and their decrease over time were very similar to those reported for the men’s junior national team [14]. In case of the male ice hockey players, however, there were no interventions addressing sleeping conditions as for the current sample of female youth athletes. Like the men’s youth ice hockey team, the German team won the tournament, although one quarter of the team showed excessive daytime sleepiness and poor sleep quality was found in a third of all players at the end of the TC. The cause for these striking values could be a lack of sleep quality characteristics and sleep duration. Whether further improvement of performance could have been achieved by greater improvement in sleep parameters or whether a temporal neglect of sleep quality during tournament phases is tolerable needs to be specifically examined [14]. Follow-up assessments including frequent measurements covering season and off-season phases as well as pre- and post-competition periods would provide a more comprehensive view of players’ sleep and daytime sleepiness. This would in turn enable a differentiation between temporary sleepiness and impaired sleep quality during (preparation for) championship periods and continuous and long-lasting disturbed sleep going beyond tournament phases.

Regarding position-specific differences, the lower sleep quality in F compared to D and G at both measurements might be explainable by their higher performance demands causing potentially stronger interference with sleep quality due to higher levels of post-practice or post-competition muscle soreness or pain [12], and possibly due to a higher level of responsibility. As with sleep quality, the daytime sleepiness of F was slightly higher at the first measurement. The development of daytime sleepiness of D and G over time, however, was contrary to the development observed in F and the whole team, as it increased at the end of the TC. Possibly, the D and G experienced training sessions or test games during the TC as more intense and demanding than the group of F, which may have caused an increase in daytime sleepiness and fatigue but did not interfere with sleep quality. The possible effects of performance demands and training intensity on sleep should be investigated in more detail in future research, considering and integrating objective training parameters. The chosen group formation of building the DG out of D and G might have been another influencing factor, as the demands of G and D differ [13]. Differences between player positions should be assessed in a larger sample of female athletes, including young and adult athletes and a sufficient number of players in all three positions. Furthermore, differences in performance demands might be reflected in different recovery patterns and needs, rather than having a direct effect on sleep. Therefore, future research on the interactions between performance demands, recovery, and sleep is required.