*3.1. Reliability*

Similar SJ (test = 29.6 ± 6.0 cm; retest = 30.8 ± 6.6 cm), CMJ (test = 31.9 ± 6.6; retest = 34.2 ± 6.9 cm) and CMJAS (test = 39.4 ± 9.7 cm; retest = 39.7 ± 10.0 cm) values were observed between testing sessions in male recreationally active adults. Non-significant differences (*p* > 0.05) were observed between testing sessions for SJ (ES = trivial; CI 95% (0.4; 2.1)), CMJ (ES = small; CI 95% (1.6; 2.9)), and CMJAS (ES = trivial; CI 95% (−0.5; 1.1)) as observed in Table 2. High test-retest reliability (ICC > 0.93; TE < 5% for CMJ and CMJAS, respectively) was observed for all measures.



Abbreviations: SJ, squat jump; CMJ, countermovement jump; ES, effect size; Diff, difference; CI, confidence interval; ICC, intraclass correlation coefficient; TE, typical error; CV, coefficient of variation; SWC, smallest worthwhile change.

Table 3 shows the test retest results for SJ (test = 23.9 ± 6.0 cm; retest = 25.8 ± 6.8 cm), CMJ (test = 26.8 ± 6.3; retest = 27.3 ± 6.2 cm), and CMJAS (test = 29.3 ± 6.0 cm; retest = 30.2 ± 6.4 cm) in female recreationally active adults. There were no significant differences (*p* > 0.05) between testing sessions for SJ (ES = small; CI 95% (1.0; 2.8)), CMJ (ES = trivial; CI 95% (−0.1; 1.1)), and CMJAS (ES = trivial; CI 95% (0.2; 1.6)). High test-retest reliability (ICC > 0.94; TE < 5% for CMJ and CMJAS, respectively) was observed for all measures.

#### *3.2. Test Usefulness*

The TE for SJ for both male and female participants was greater than the presumed SWC; consequently, these measures were rated as "marginal." In contrast, TE for CMJ and CMJAS for both genders were similar or lower than SWC and was rated as "OK" and "good".


**Table 3.** Test-retest reliability and usefulness of My Jump 2 in female recreationally active adults.

#### *3.3. The Validity of the Test*

There were no significant differences (*p* > 0.05) between the My Jump 2 app and Optojump for all jumps in male participants with trivial effects size (from −0.03 to −0.09) (Table 4). Very large correlations were observed between the My Jump 2 app and Optojump for SJ (r = 0.95, *p* = 0.001), CMJ (r = 0.98, *p* = 0.001), and CMJAS (r = 0.98, *p* = 0.001).

**Table 4.** Descriptive statistics and validity analysis in male recreationally active adults based on Pearson's r.


Abbreviations: r, Pearson's correlation coefficient.

Similar results were obtained for female recreationally active adults (Table 5). No significant differences (*p* > 0.05) were observed between the My Jump 2 app and Optojump for all jumps in female recreational athletes with trivial effects size (from −0.09 to −0.19). Very large correlations were observed between the My Jump 2 app and Optojump for all jumps (r > 0.94, *p* = 0.001).

**Table 5.** Descriptive statistics and validity analysis in female recreationally active adults based on Pearson's r.


Figures 2–4 show the level of agreemen<sup>t</sup> for all jumps. Bland and Altman's plot depicting limits of agreemen<sup>t</sup> for SJ height between the Optojump and My Jump 2 show that the majority of data points are within the 95% CI's (Figure 2).

Further analysis of the Bland–Altman plots in male athletes revealed very low R<sup>2</sup> values (R<sup>2</sup> ≤ 0.10), meaning outcomes estimated from My Jump 2 had no predisposition to overestimate or underestimate jump performance. On the contrary, in female participants, the plot shows bias related to the magnitude of jump height (R<sup>2</sup> = 0.74), such that, at lower jump heights, values derived from Optojump data tended to be higher than those from My Jump 2, resulting in positive difference scores. Moreover, the mean bias between the two methods for all jumps was 0.51 cm.

**Figure 2.** Level of agreemen<sup>t</sup> (Bland–Altman) with 95% limits of agreemen<sup>t</sup> (dashed lines) and the mean difference (solid line) between My Jump 2 and the Optojump for SJ in (**A**) male and (**B**) female participants.

**Figure 3.** Level of agreemen<sup>t</sup> (Bland–Altman) with 95% limits of agreemen<sup>t</sup> (dashed lines) and the mean difference (solid line) between My Jump 2 and the Optojump for CMJ in (**A**) male and (**B**) female participants.

**Figure 4.** Level of agreemen<sup>t</sup> (Bland–Altman) with 95% limits of agreemen<sup>t</sup> (dashed lines) and the mean difference (solid line) between My Jump 2 and the Optojump for CMJAS in (**A**) male and (**B**) female participants.
