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Functional ankle instability (FAI) afflicts many athletes. Several causes of FAI have been implicated, including peroneal muscle weakness. Traditional musculoskeletal rehabilitation programs have focused on concentric muscle strength. The purpose of our study was to compare concentric and eccentric isokinetic and isometric eversion ankle strength measurements between subjects identified as having unilateral FAI and subjects having no history of inversion ankle sprain.
Employing a matched-pairs technique, subjects with no history of ankle injury were compared with subjects with unilateral FAI using isokinetic and isometric measures of eversion ankle strength. Strength testing was performed in a sports medicine clinic setting.
Forty-two subjects volunteered for this study: 21 subjects suffered from unilateral FAI (age = 19.3 ± 1.1 years, wt = 84.0 ± 9.5 kg, ht = 181.5 ± 9.2 cm), while 21 subjects served as matched-paired controls (age = 19.5 ± 1.2 years, wt = 82.5 ± 10.9 kg, ht = 179.5 ± 7.9 cm).
Ankle eversion concentric and eccentric strength (peak torque) was assessed at 0°/s, 30°/s, 60°/s, 90°/s, 120°/s, 150°/s, and 180°/s using an isokinetic dynamometer.
We found no significant differences in concentric, eccentric, or isometric eversion ankle strength between the 2 groups of subjects.
The exact cause of FAI remains elusive. Based on our results, those who suffer from unilateral FAI do not appear to have eversion strength deficits. Unless clear evidence of weakness exists, clinicians may find that eversion strength training exercises are unnecessary. Future research should examine other causes of FAI, including reciprocal muscle group strength ratios and proprioception deficits.