When walking, step length provides critical information on travelled distance along the ongoing path. Little is known on the role that knowledge about body dimensions plays within this process. Here we directly addressed this question by evaluating whether changes in body proportions interfere with computation of travelled distance for targets located outside the reaching space. We studied locomotion and distance estimation in an achondroplastic child (ACH, 11 yr) before and after surgical elongation of the shank segments of both lower limbs and in healthy adults walking on stilts, designed to mimic shank segment elongation. Kinematic analysis of gait revealed that dynamic coupling of the thigh, shank and foot segments changed substantially as a result of elongation. Step length remained unvaried, in spite of the significant increase in total limb length (~1.5 times). These relatively shorter strides resulted from smaller oscillations of the shank segment, as would be predicted by proportional increments in limb size, and not by asymmetrical segmental increment as in the present case (thighs' length was not modified). Distance estimation was measured by walking with eyes closed towards a memorized target. Before surgery, the behaviour of ACH was comparable to that of typically developing participants. In contrast, following shank elongation, ACH walked significantly shorter distances when aiming at the same targets. Comparable changes in limb kinematics, stride length and estimation of travelled distance were found in adults wearing on stilts, suggesting that path integration errors in both cases were related to alterations in the inter-segmental coordination of the walking limbs. The results are consistent with a dynamic locomotor body schema used for controlling step length and path estimation, based on inherent relationships between gait parameters and body proportions.