Strength, muscular endurance, and flexibility are important components of healthy back function. This study determined the reliability and evaluated the validity of selected low back field tests (FITNESSGRAM ® Trunk Extension [FG-TE] and Box 90° Dynamic Trunk Extension [B-90° DTE]) when compared to laboratory tests (Parallel Roman Chair Dynamic Trunk Extension [PRC-DTE], Parallel Roman Chair Static Trunk Extension [PRC-STE], and Dynamometer Static Back Lift [DSBL]).
Forty males age 15.1 ± 1.2 yr and 32 females age 15.5 ± 1.2 yr participated.
Intraclass test-retest reliability coefficients (one-way ANOVA model for a single measure) ranged from .940 to .996. Validity coefficients determined by Pearson product moment correlation coefficients for males and females, respectively, were as follows: B-90° DTE vs. PRC-DTE = .82, .62 (p < .05); B-90° DTE vs. PRC-STE = .55, .38 (p < .05); B-90° DTE vs. DSBL = −.29, −.23; FG-TE vs. PRC-DTE = .23, −.11; FG-TE vs. PRC-STE = −.15, .33; and FG-TE vs. DSBL = −.04, −.36.
B-90° DTE was shown to be a valid field test when compared to PRC-DTE, but only for the males. Further research on the PRC-DTE and PRC-STE items for adolescents is recommended.