What Best Protects the Inverted Weightbearing Ankle Against Further Inversion?: Evertor Muscle Strength Compares Favorably with Shoe Height, Athletic Tape, and Three Orthoses

We measured the maximal isometric eversion moment developed under full weightbearing in 20 healthy adult men (age, 24.4 ± 3.4 years; mean ± SD) with their ankles in 15° of inversion. Tests were performed at both 0° and 32° of ankle plantar flexion in low- and in three-quarter-top shoes with and without adhesive ath letic tape or one of three proprietary ankle orthoses. At 0° of ankle plantar flexion, the mean maximal voluntary resistance of the unprotected ankle to an inversion moment was 50 ± 8 N-m; this increased by an average of 12% (or 6 N-m) when the subject wore a three- quarter-top basketball shoe. The maximal voluntary resistances to inversion moments developed with the ankles further protected by athletic tape or any of three orthoses were not significantly different. Biomechani cal calculations suggest that at 15° of inversion the fully active ankle evertor muscles isometrically developed a moment up to six times larger than that developed when an athlete wears a three-quarter-top shoe alone and more than three times larger than that developed passively when the athlete has tape or an orthosis worn inside a three-quarter-top shoe. We conclude that fully activated and strong ankle evertor muscles are the best protection for a near-maximally inverted ankle at footstrike.