| Summary: | Ankle bracing is rapidly becoming the accepted method for the prevention of inversion injuries among active individuals suffering from a chronic ankle instability. The purpose of this study was to measure the effectiveness of the non-rigid, Subtalar Stabilizer (STS) ankle brace under conditions similar to an unexpected fall which inextreme circumstances could lead to a lateral ligament injury. The "calcaneal inversion" angles, times, and forces were measured when the subject's right foot, bearing body weight, was suddenly inverted as the trap door of the support platform swung to a side slope of 22°. Thirty subjects, 15 female and 15 male participated in the study. The "overall inversion drop" was divided into two phases, "free-fall" and "loading". The results of the 2 (sex) by 4 (brace condition) ANOVAs followed by post-hoc Tukeys analyses showed the brace significantly (p<0.05) reduced the "calcaneal inversionangle" from 27.4° ± 6.1° to 18.3° ± 6.0° for the "overall drop", significantly lengthened the "inversion time" from 0.140 ± 0.040seconds to 0.184 ± 0.040 seconds for the "overall drop", and significantly reduced the "calcaneal inversion velocity" from 324.6 ±111.9 °/sec. to 165.2 ± 66.5 °/sec. during "loading", and from 278.7± 120.0 °/sec. to 183.0 ± 108.7 °/sec. for the "overall drop". Following exercise which incorporated lateral movements and sprinting, the STS ankle brace continued to provide significant(p<0.05) reduction in the "calcaneal inversion angle and velocity" however it lost some of its original effectiveness. Although the females had a significantly (p<0.05) greater "calcaneal inversion range of motion" during "loading" there was no significant difference for the "overall drop" (33.0° ± 7.0° for the females versus 29.5° ±6.5° for the males). Therefore, it was concluded that the ankles of females are not more flexible in the frontal plane than the ankles of males. This study did not support the mechanism whereby braces play a role in the prevention of inversion injuries by enhancing afferent nerve fibres in order to prematurely stimulate the
protective peroneal muscles. Evidence indicates that it is more likely that the brace functions to limit motion by redistributing and supporting a proportion of the load experienced by the lateral ligaments of the ankle during sudden inversion. The results of this study suggest that the non-rigid STS ankle brace has at least a "four fold" purpose in its role in the prevention of inversion injuries: 1) to significantly restrict the degree of "calcanealin version range of motion" during an unexpected fall and 2) to significantly lengthen the time of inversion thereby decreasing the rate at which the calcaneus inverts during a sudden inversion drop,3) to maintain this support, significantly, following sprinting and lateral movement exercise, and 4) to provide a relatively equal amount of ankle restriction of motion for both active males and females.
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