Letter to the Editor: Caution Needed in Interpreting Step-to-Step Transitions in Stroke Rehabilitation

This Letter to the Editor addresses key methodological and interpretative issues in a recent study by Covarrubias-Escudero et al.(https://doi.org/10.1002/pri.70080), which examined the effects of functional electrical stimulation (FES) on step-to-step transitions (STS) in individuals with chronic stroke. While the authors provide valuable insights into center-of-mass (CoM) mechanics during gait, we raise several concerns regarding the study's experimental design and data interpretation. First, the absence of controlled walking speed limits the ability to distinguish between genuine changes in transition strategy and speed-related adaptations, particularly since FES tends to increase gait velocity. Second, the lack of bilateral or limb-specific analysis restricts conclusions about gait asymmetry, a central feature of post-stroke locomotion. In addition, ambiguity surrounding the definition and computation of vertical velocity of the CoM (V_{v CoM}) calls into question the reliability of this outcome measure. Specifically, the methods used to estimate CoM dynamics are not fully described, which weakens confidence in the reported effects. Finally, the use of peak vertical ground reaction forces (GRF_v) may not be appropriate in pathological gait, where clear force maxima are often absent, and average-based metrics could offer more reliable alternatives. We conclude that future studies should emphasize speed standardization, bilateral analyses, and transparent methodological reporting to strengthen the clinical and scientific value of biomechanical assessments in stroke rehabilitation.