The relationship between excessive pronation as measured by navicular drop and isokinetic strength of the ankle musculature.

EMG research has shown that excessive pronation affects the timing and magnitude of extrinsic muscle activity. This study was designed to investigate the relationship between excessive pronation and isokinetic strength of the ankle. The following measures were performed on 24 subjects (12 pronators, 12 normals) matched for gender and weight: 1) plantarflexion, dorsiflexion, inversion and eversion strength, both eccentrically and concentrically, determined by isokinetic peak torque at 30 degrees/sec; and 2) excessive pronation determined by navicular drop. Subjects with excessive pronation were found to have no difference in invertor strength, but decreased concentric plantarflexion strength when compared to normals. This finding agrees with biomechanical theory suggesting that a pronated foot is less rigid and generates less torque. Differences in strength ratios in excessive pronators were also observed and attributed to the decrease in plantarflexion strength.