Reliability and Validity of Ankle Muscle Strength Testing Using the ISOTIB Device

One repetition maximum (1RM) testing is recognised as a reliable and valid method for determining maximum muscle strength. However, there are limited reports in the literature for measuring maximum ankle strength using free-weight methods. The aim of this study was to determine the test-retest reliability and concurrent validity of a novel free-weight device (ISOTIB) used to measure ankle strength.

Fifteen healthy, recreationally active, adults (male = 10, female = 5, age = 29.7 ± 4.4 years) volunteered for the study, attending two sessions 1 week apart. Reliability was assessed using intraclass correlation coefficients (ICC_(3,1)) and Bland-Altman method. Concurrent validity was examined by comparing 1RM ankle strength and normalised muscle activity using surface electromyography (sEMG) during dorsiflexion, inversion, and eversion movements performed with the ISOTIB device and an isokinetic dynamometer.

The ISOTIB exhibited excellent test-retest reliability for maximal dorsiflexion (ICC_(3,1) = 0.99, 95% CI: 0.977-0.997), inversion (ICC_(3,1) = 0.99, 95% CI: 0.970-0.997), and eversion (ICC_(3,1) = 0.97, 95% CI: 0.920-0.991) strength. Concurrent validity was confirmed, with high positive correlations for maximal dorsiflexion (r = 0.90, 95% CI: 0.72-0.97) p < 0.001), inversion (r = 0.67, 95% CI: 0.24-0.88) p < 0.007), and eversion (r = 0.87, 95% CI: 0.64-0.96) p < 0.001) strength. sEMG results supported concurrent validity with comparable activity in the tibialis anterior, peroneus longus, and peroneus brevis muscles.

The ISOTIB demonstrated excellent reliability and validity, suggesting it is a viable tool for assessing maximal ankle strength. The ISOTIB offers a practical alternative to current methods, which are typically expensive and utilise large immovable devices.