AbstractThis study aimed to assess the responsiveness to the rehabilitation of three trunk acceleration-derived gait indexes, namely the harmonic ratio (HR), the short-term longest Lyapunov’s exponent (sLLE), and the step-to-step coefficient of variation (CV), in a sample of subjects with primary degenerative cerebellar ataxia (swCA), and investigate the correlations between their improvements (∆), clinical characteristics, and spatio-temporal and kinematic gait features. The trunk acceleration patterns in the antero-posterior (AP), medio-lateral (ML), and vertical (V) directions during gait of 21 swCA were recorded using a magneto-inertial measurement unit placed at the lower back before (T0) and after (T1) a period of inpatient rehabilitation. For comparison, a sample of 21 age- and gait speed-matched healthy subjects (HS_matched) was also included. At T1, sLLE in the AP (sLLE_AP) and ML (sLLE_ML) directions significantly improved with moderate to large effect sizes, as well as SARA scores, stride length, and pelvic rotation. sLLE_ML and pelvic rotation also approached the HS_matched values at T1, suggesting a normalization of the parameter. HRs and CV did not significantly modify after rehabilitation. ∆sLLE_ML correlated with ∆ of the gait subscore of the SARA scale (SARA_GAIT) and ∆stride length and ∆sLLE_AP correlated with ∆pelvic rotation and ∆SARA_GAIT. The minimal clinically important differences for sLLE_ML and sLLE_AP were ≥ 36.16% and ≥ 28.19%, respectively, as the minimal score reflects a clinical improvement in SARA scores. When using inertial measurement units, sLLE_AP and sLLE_ML can be considered responsive outcome measures for assessing the effectiveness of rehabilitation on trunk stability during walking in swCA.