## 4 Discussion  
### Reliability, Validity and Aerobic Capacity Assessment  
Table 3 shows the research that includes verification of reliability, validity and aerobic capacity assessment of the IFT 30-15. [PERSON] and [PERSON] [25] conducted a six-week strengthening intervention that involved a sample of 26 female sub-elite netball players and compared 30-15 IFT scores and Yo-yo IRT 1 level scores. The results indicate a very strong relationship between these two tests. The authors propose the 30-15 IFT for measuring HII (high-intensity intermittent-based running performance) and indicate that this test is suitable for the abovementioned purpose [25]. Regarding the elite futsal players (ICC = 0.92) and female players (ICC = 0.96), this test, including the Vift value, also proved to be reliable [26]. [PERSON] et al. performed checks of 30-15 IFT validity in four rugby leagues and found that the test was valid [27]. Furthermore, [PERSON] et al. [15] also confirmed the validity and reliability of this test for the assessment of intermittent aerobic fitness with a sample of 17 elite soccer players (Vift--ICC = 0.91; CV = 1.8%; HRpeak--ICC = 0.94; CV = 1.2%; and VO2 max--ICC = 0.94; CV = 1.6%). Another study, confirmed by the previous one, was conducted on a sample of 14 soccer players in order to verify the reliability of the test. The authors of this study concluded that the test was reliable (CV = 2.5%) for the evaluation of cardiorespiratory fitness specific to team sports [1]. Similar observations and similar conclusions were made by other authors, who also found the IFT 30-15 to be a reliable and useful field test for assessment of cardiorespiratory fitness of young rugby league players [27]. [PERSON], as the originator and creator of the abovementioned test, discovered in his research a high correlation between the results of the 30-15 IFT and those of the Yo-Yo IR1 (r = 0.75; 90%; CL = 0.57; 0.86). However, he eventually concluded that it was possible that the two tests might be assessing slightly different physical characteristics and capacities but that the sensitivity to training in both tests was almost equal [28]. [PERSON] et al. [16] studied the reliability of the 30-15 IFT, comparing it with the treadmill test. The respondents were young female elite basketball players. This study arrived at the following results: VO2 max (CV = 4.9%, ICC = 0.85), VIFT (CV = 6.0%, ICC = 0.85) and Hrmax (CV = 4.8%, ICC = 0.96), based on which the author concluded that the 30-15 IFT is a practical way to assess the fitness abilities of young female basketball players. [PERSON] et al. [18] conducted research where they tried to determine the reliability of the 30-15 IFT-28m test on a sample of 10 elite wheelchair rugby players. The authors concluded, based on gathered results, that the test is reliable when used on these respondents (30-15 IFT28m, CV = 1, 9%, ICC = 0, 99; Peak heart rate, CV = 4, 5%, ICC-0.95; Blood lactate (CV = 5, 5%, ICC = 0.98). There are studies that have compared the submaximal and maximal cardiorespiratory response between 30-15 IIT and 30-15 IFT on a sample of 10 semi-professional hockey players [29]. They concluded that, compared to the field test (30-15 IFT), maximal cardiorespiratory responses (HRpeak and VO2 peak) on the 30-15 IFT were lower, while the maximal lactate was higher during the 30-15 IFT. This overview study shows that 30-15 IFT has an excellent reliability relating to VO2 max testing, as demonstrated by high ICC values (\(\geq\)0.85) and low CV values (\(\leq\)4.9). In addition, it shows an outstanding reliability with regard to VIFT, which is demonstrated by high ICC values (\(\geq\)0.85) and low CV values (\(\leq\)6.0). The 30-15 IFT proved to be reliable for both Hrmax and HRpeak based on the retrospectively provided values (CV = 4.8%, ICC = 0.96; ICC = 0.94 n CV = 1.2%).