Active and passive anterior translational shoulder impedance varies inversely with perturbation amplitude

Evaluating active translational shoulder stability is essential to quantifying clinically-relevant deficits in individuals with shoulder instability. Estimating impedance with random perturbations allows for this assessment of active translational stability that is not possible with clinical techniques. Given the presence of amplitude dependence in previous rotational joint impedance studies, our objective was to quantify passive and active anterior translational shoulder impedance while varying perturbation amplitude. Our results displayed decreases in impedance at increasing amplitudes that were slightly more pronounced during active conditions. These results highlight the sensitivity of translational shoulder impedance to perturbation amplitude and inform the proper interpretation of translational impedance during future experimental paradigms.