Validity and Reliability of an Adapted Leg/Back Isometric Strength Testing Device

Abstract

The leg/back dynamometer (LBD) is a valid lower-body strength test. For people stronger than the typical device, a crane scale could provide an adapted leg/back dynamometer (ALBD), although validity and reliability analyses are needed. Fifty participants completed three testing sessions, consisting of three LBD and ALBD trials each. One-sample t-tests determined whether LBD and ALBD mean differences were significant compared to 0. Paired samples t-tests and effect sizes (d) compared average and maximum LBD and ALBD. Pearson’s correlations and regression derived LBD and ALBD relationships. Intra-class correlation coefficients (ICC) and coefficient of variation (CV) assessed reliability. A three-way repeated measures ANOVA compared between-session LBD and ALBD. Test usefulness was analyzed by typical error (TE) and smallest worthwhile change (SWC). The mean differences analyses indicated a fixed bias (p≤0.04); the LBD recorded greater values than the ALBD (p<0.01; d=0.43-0.89). Relationships between the LBD and ALBD across all sessions were significant (p<0.001; r=0.902-0.985), with 94% explained variance. The ICCs and CVs for all sessions were acceptable (ICC≥0.97; CV≤6%). There were no significant LBD or ALBD differences between Sessions 1 or 2. However, average and maximum LBD for Session 3 was greater than Sessions 1 and 2; Session 3 average ALBD was greater than Sessions 1 and 2 (p≤0.002); and maximum ALBD was greater than Session 1 (p≤0.042). The LBD and ALBD were useful (TE=5.13-5.65kg; SWC=7.26-7.99kg). The ALBD can measure strength, although the data was lower than the LBD. The LBD and ALBD are reliable and useful; two practice sessions could enhance reliability.