Correlation between gait quality, walking speed, and endurance and their changes in patients with cerebral palsy: improved quality does not always mean faster walking or greater distance

Cerebral palsy (CP) is a nonprogressive brain disorder that causes permanent movement and posture impairments, often resulting in gait dysfunction. Improving walking ability is a key therapeutic goal, as it enhances daily functioning and social participation. Gait quality, walking speed, and endurance are commonly assessed using the Gait Deviation Index (GDI), gait velocity ( v ), and the six-minute walk test (6MWT). Although these measures are widely used, it remains unclear how strongly they are related to one another and whether their changes over time follow similar patterns. Importantly, each feature is assessed with different procedures and practical constraints, which may limit joint interpretation in routine clinical practice. Therefore, this study aimed to quantify the relationships between GDI, gait velocity, and distance measured during the 6MWT (6MWT distance) in ambulatory individuals with CP and to determine whether their changes follow a similar pattern over time. In total, 360 ambulatory participants with spastic CP (Gross Motor Function Classification System (GMFCS) I–III) were assessed twice over a 24-month period (T1: first assessment; T2: 24 months later; paired T1–T2 data were available for N=211). Gait quality (GDI), walking speed (velocity), and endurance (6MWT distance) were measured using instrumented gait analysis and standardized protocols. Correlations between these measures were analysed using Pearson’s or Spearman’s coefficients, with significance set at p < 0.05. At baseline (T1), in the entire group, the GDI was moderately correlated with gait velocity (p < 0.01, r = 0.59) and strongly correlated with 6MWT distance (p < 0.01, r = 0.61); gait velocity and 6MWT distance were also strongly correlated (p < 0.01, r = 0.61). In subgroup analyses, significant baseline correlations of varying strength were observed across all the subgroups. For changes from T1 to T2, correlations in the entire group were very weak for changes in GDI vs. changes in gait velocity (p = 0.03, r = 0.15) and for changes in GDI vs. changes in 6MWT distance (p = 0.02, r = 0.16); changes in gait velocity had a stronger correlation with changes in the 6MWT, but this correlation was still weak (p < 0.01, r = 0.26). Significant correlations between changes in the mentioned parameters occurred only in selected subgroups, again with varying strength. Gait quality, walking speed, and gait endurance are correlated in individuals with CP, and the strength of these relationships depends on the level of ambulatory function. Although gait quality changed over time, its change showed only very weak associations with changes in walking speed and gait endurance; in independently ambulant participants (GMFCS I–II), changes in the GDI were not associated with changes in velocity or walking distance, whereas in participants with GMFCS III, improvements in gait quality aligned with longer walking distance but not with higher velocity. Overall, these findings support a pragmatic, individualized approach to clinical assessment, guided by patients’ ambulatory function level and the limitations of the GDI for interpreting longitudinal change. Institutional Review Board permission no. 767/24.