The Reliability of Common Functional Performance Tests within an Experimental Test Battery for the Lower Extremities

The main aim of this study was to determine the test–retest reliability of an experimental functional test battery: Y-balance test (YBT), single-leg countermovement jump (SLCMJ), single-leg hop for distance (SLH), side-hop (SH), speedy-jump (SJ), agility-T (AT), and lower extremity functional test (LEFT). Secondary aims were (1) to determine the mean range for the limb symmetry index (LSI) and (2) to detect significant differences in performance between test–retest sessions. Twenty-two healthy adults (14 males, 8 females; age 23.3 ± 3.9) were tested by the same rater during two different sessions (T1–T2), with a seven-day interval, under the same conditions. Reliability analysis showed good-to-excellent reliability (0.89 < ICC < 0.97; 0.80 < α < 0.98) for the test battery. LSI ranged from 95.9 ± 6.7% (SH-T1) to 104.4 ± 12.5% (SLCMJ-T2). Repeated measures ANOVA detected significant performance differences between sessions in the LEFT (p = 0.009) and for non-dominant sides in the SLH (p = 0.015), SH (p = 0.007), and SJ (p = 0.011). The high reliability of the test battery suggests a potential use in clinical sports practice. The LSI range of ≥95% was proposed as a benchmark for healthy adults. Learning effect seems to have played a crucial role in the T2 improvements of the non-dominant side for hop performances (SLH, SH, SJ) and speed performance (LEFT).