Noise-Enhanced Eversion Force Sense in Ankles With or Without Functional Instability

Context: Force sense impairments are associated with functional ankle instability. Stochastic resonance stimulation (SRS) may have implications for correcting these force sense deficits. Objective: To determine if SRS improved force sense. Design: Case-control study. Setting: Research laboratory. Patients or Other Participants: Twelve people with functional ankle instability (age = 23 +/- 3 years, height = 174 +/- 8 cm, mass = 69 +/- 10 kg) and 12 people with stable ankles (age = 22 +/- 2 years, height = 170 +/- 7 cm, mass = 64 +/- 10 kg). Intervention(s): The eversion force sense protocol required participants to reproduce a targeted muscle tension (10% of maximum voluntary isometric contraction). This protocol was assessed under SRSon and SRSoff (control) conditions. During SRSon, random subsensory mechanical noise was applied to the lower leg at a customized optimal intensity for each participant. Main Outcome Measure(s): Constant error, absolute error, and variable error measures quantified accuracy, overall performance, and consistency of force reproduction, respectively. Results: With SRS, we observed main effects for force sense absolute error (SRSoff = 1.01 +/- 0.67 N, SRSon = 0.69 +/- 0.42 N) and variable error (SRSoff = 1.11 +/- 0.64 N, SRSon = 0.78 +/- 0.56 N) (P < .05). No other main effects or treatment-by-group interactions were found (P > .05). Conclusions: Although SRS reduced the overall magnitude (absolute error) and variability (variable error) of force sense errors, it had no effect on the directionality (constant error). Clinically, SRS may enhance muscle tension ability, which could have treatment implications for ankle stability.