*2.4. Physical Fitness*

For testing the physical fitness, participants completed the German Motor Performance Test (GMT) 6-18 [21]. The GMT is a standardized test battery consisting of eight items that assesses various subdomains of physical fitness: 20 m sprint (sprint velocity), balancing backwards on three 3 m long beams with different width (coordination in a task requiring precision), jumping sidewards over a middle line for 15 s (coordination under time pressure), stand-and-reach (flexibility), push-ups in a period of 40 s (strength endurance), sit-ups in a period of 40 s (strength endurance), standing long jump (power), and 6 min run (endurance). With regard to the performance criteria of GMT 6-18, the inter-rater reliability (0.95) and test–retest reliability (0.82) of the test battery were good, and the battery has been validated for assessing speed, coordination, flexibility, strength, and endurance [21]. According to the exact instruction of the test manual by Bös [21], tests were carried out by trained physical education students in the gymnasiums of the participating schools. All tests were completed during a single session, lasting about 90 min in random order, except for the 20 m sprint, which was completed at the beginning, and the 6 min run, which was completed at the end of the testing session. Values of the eight test items were standardized according to age and sex-reference values resulting in so-called Z-values, with a value of 100 representing average performance in the tests. According to Bös [21], the formula for the standardization is

$$\mathbf{Z} = (\mathbf{x}\_{i} - \mathbf{M}) / \mathbf{SD} \times 10 + 100 \tag{1}$$

where x<sup>i</sup> is the raw value of the test item, M is the mean, and SD the standard deviation of the age- and sex-specific norm sample. Values above 100 indicate above-average performance and values below 100 indicate below-average performance. The average of all scores was used as an indicator for overall physical fitness [21].
