Strength−Duration Curves of the Common Fibular Nerve Show Hypoexcitability in People With Functional Ankle Instability

Abstract Background Some motor impairments, such as decreased reaction of peroneal muscles, altered kinematic, or poor postural control, have been described in people with functional ankle instability. Evidence shows a possible relationship between fibular nerve impairments and functional ankle instability. Objective To investigate the electrophysiologic excitability of the common fibular nerve, as measured by Strength–Duration curves, in subjects with functional ankle instability compared with a control group without ankle impairment. Design A cross-sectional study. Setting University Research laboratory. Participants Fifty subjects with functional ankle instability (35 men, 15 women; ages 24.36 ± 5.01 years) and 63 uninjured control patients (44 men, 19 women; ages 22.67 ± 4.85 years) were recruited by convenience sampling. Interventions Not applicable. Main outcome measures Strength–Duration curves of the common fibular nerve were made in all participants. Rheobase, chronaxie, Bawen index, accommodation index, galvano-tetanic threshold, and intensity thresholds for different pulse durations were obtained and compared between the 2 groups. Results Subjects with functional ankle instability show increased values of chronaxie (0.58 ± 0.24 ms versus 0.47 ± 0.16 ms; P = .004), Bawen index (1.53 ± 0.24 versus 1.39 ± 0.21; P = .002), and intensity thresholds for pulse durations ≤2 ms both for rectangular and triangular pulse wave forms. The accommodation index was smaller in subjects with functional ankle instability than controls (3.7 ± 0.72 versus 4.05 ± 0.98; P = .036). The remaining parameters did not show significant differences between groups. Conclusions These findings suggest that subjects with functional ankle instability show a decreased excitability in their common fibular nerve when compared with subjects without ankle injuries.