The Reliability and Validity of a Novel Ankle Isometric Plantar Flexion Strength Test

Abstract

Context: Strengthening of ankle plantar flexor muscles is one of the important components in the rehabilitation of many lower limb injuries and disorders. However, there are few simple methods to evaluate ankle plantar flexor strength in clinical situations without using equipment. The purpose of this study was to verify the intraexaminer and interexaminer reliability and the concurrent validity of a novel ankle isometric plantar flexion (PF) strength test (PF break test [PFBT]). Design: Case–control study. Methods: The intraexaminer and interexaminer reliabilities of the PFBT were evaluated in 57 orthopedic patients and 30 healthy adults. The range of motion of the ankle joint and the number of heel raises were compared between positive and negative PFBT cases. Then, isometric ankle PF torque (ankle PF of 0°, 15°, and 30°) was compared in knee extension and in the 50° flexion position between positive and negative PFBT cases in 30 healthy adults. Results: The intraexaminer reliability (κ) of the PFBT was .81 to .94, and the interexaminer reliability (κ) was .37 to .74. The PFBT positive group had a significantly smaller range of motion in the ankle joint (P < .05) and a significantly lower number of heel raises (P < .001) than the PFBT negative group in orthopedic patients, but no significant differences in healthy adults. The PFBT positive group had less ankle PF torque than the PFBT negative group at all ankle PF angles (P < .01). The isometric PF torque in the end range of ankle PF in knee extension could predict the results of the PFBT and correctly classified 90.0% of cases (P < .001). Conclusion: The PFBT is considered a simple and valid method to evaluate isometric ankle PF strength in the clinical setting.