Statistical analysis
For the statistical analysis of the demographic, physical activity, and juggling performance data, SPSS Statistics (version 27.0; IBM, New York, USA) was used. All the analyses were performed after checking for normal distribution of the data via the Shapiro–Wilk test, and the level of significance was set to 5%. When the data were normally distributed, mixed analyses of variance (ANOVAs) with factor interaction (time × group) were used. We applied Greenhouse–Geisser correction, if the Mauchly’s sphericity test had been significant. If a significant interaction effect (time × group) was observed, post hoc tests were performed via paired t-tests within groups applying Bonferroni–Holm corrections (Holm To determine intervention-related changes in GM volume, we employed a flexible factorial model with the factors group (IG, CG) and time (week 0, week 6, and week 12) implemented in SPM12. Since we were interested in time-dependent changes, only within-group changes over the different time points of assessment were computed. Therefore, we did not include age, sex, or total intracranial volume as covariates. An absolute threshold of 0.1 was applied to exclude voxels with a probability of having less than 10% GM. We then compared the changes in all three time points (week 0 vs. week 6, week 6 vs. week 12, and week 6 vs. week 12) within each group. Finally, statistical thresholds were set using a cluster-level 