We have recently shown that soccer players may benefit from acute sleep hygiene (SH) strategies to reduce the time to sleep onset after late-evening training session (Vitale et al., 2019a). In detail, soccer players allocated to an experimental group (EG, n = 17; age: 26 [+ or -] 6 years; height: 1.77 [+ or -] 0.06 m; body mass 72 [+ or -] 6 kg) exhibited lower sleep latency (-47%; p = 0.021, ES = 0.6) and better subjective sleep quality (+11.0%, p = 0.004, ES = 0.8) respect a control group (CG, n=12; age: 25[+ or -]7 years; height: 1. 76 [+ or -] 5 m; body mass 75 [+ or -] 11 kg) in response to a SH protocol after a late evening small-sided-game (SSG).
During this study, we collected saliva samples (Salivette, Sarsted AG & CO, Numbrecht, Germany) for evaluating salivary cortisol (Salivary cortisol kit, DiaMetra, DKO020) before (PRE), and after (POST), and before going to bed (POST 1) the SSG session. The cortisol awakening response (CAR) was also evaluated 30 min after morning awaking. Descriptive statistics (mean [+ or -] SD) for the outcome measures were calculated. The normality of the distribution of salivary cortisol was checked with the Shapiro--Wilk test and two-way analysis of variance was used to test intra- and inter-group differences for salivary cortisol concentration. When a significant effect occurred, a Bonferroni's multiple comparisons test was applied. The magnitude of change after the acute sleep strategy and differences between groups were analyzed by means of a modified statistical spreadsheet, which calculates the standardized differences, or effect sizes (ES) (Hopkins et al., 2009).
Figure 1 and Table 1 present the mean ([+ or -]SD) and the raw data of salivary cortisol samples in the different time points in EG and CG. Significant intergroup variation in salivary cortisol levels in EG in PRE versus POST (p = 0.0005, ES: [greater than or equal to] 2.0 [+ or -] 0.3, most likely), POST versus POST 1 (p = 0.036, ES: 1.4 [+ or -] 0.2, very likely), POST 1 versus CAR (p
Overall, we observed that EG and CG demonstrated similar salivary cortisol concentrations at baseline and in response to a late-night soccer-specific training session. However, comparison of acute post intervention sleep hygiene in EG showed a reduction of CAR in EG as compared with CG. According to the objective and subjective data of our previous work (Vitale et al., 2019a) we could hypothesized that players that carried out the SH...