A Study on the Intersection of Ground Reaction Forces during Overground Walking in Down Syndrome: Effects of the Pathology and Left–Right Asymmetry

Abstract

Motor dysfunctions in patients with Down Syndrome (DS) result in poor locomotion and an altered gait phenotype, characterized by compromised stability management and frequent bilateral asymmetries. Directing ground reaction forces to a point above the center of mass, referred to as the virtual pivot point (VPP), is one means of maintaining stability during walking. This cross-sectional observational study compared the dynamic gait function of 33 individuals with DS (mean age: 17.7 ± 6.4 years, 13 females) to a group of 36 healthy controls (mean age: 15.5 ± 6.1 years, 15 females), using the concept of the VPP. Results showed that the VPP was located more anteriorly in individuals with DS compared to healthy controls, with no differences in the variability (R2) or symmetry of VPP coordinates. This anterior VPP position is likely due to the larger hip moments observed in patients with DS during the propulsive phase of stance. High R2 values in DS suggest that the VPP is strongly related to dynamic stability during walking.

Walking like a robot: do the ground reaction forces still intersect near one point when humans imitate a humanoid robot?

“…Analogous to the VPP model, an intersection point of the GRFs above the CoM could also be found in various experimental studies for human walking [ 5 , 10 – 14 ], and even for some animals such as dogs [ 5 , 15 ], macaques [ 16 ] and quails [ 17 ]. In those experiments, the GRFs point to the VPP with a small spread.…”

“…Additionally, the CoMz shifts downward by approximately 5 cm each for the crouched walking and for the walking with added masses compared with the control condition (figure 4b). Both effects increase the VPP height [42]. The slower walking speed causes a smaller ratio of horizontal GRFs in GRF magnitude (figure 4c,d), which shifts the VPP upward [42].…”

“…Both effects increase the VPP height [42]. The slower walking speed causes a smaller ratio of horizontal GRFs in GRF magnitude (figure 4c,d), which shifts the VPP upward [42].…”

Virtual pivot point: Always experimentally observed in human walking?

“…Based on statements of Herr & Popovic [19], here the VPP was defined as a point if R 2 was greater than 0.6, separately for each condition. For each trial, the VPP position was only considered if the VPP was classified as a point (for more details concerning the VPP calculation see [16]). For the analyses, the anterior-posterior (x) direction and the vertical (z) direction were considered.…”

“…Thus, in this study it is hypothesized that (1) for walking with modified foot rollover a VPP could be observed, but the position will change. If the range of the CoP motion relative to the horizontal CoM position becomes smaller, the VPP is shifted down [16]. For walking with a plank the range will presumably be smaller than for walking with shoes since the foot lift-off will take place further ahead in the foot due to the limited rollover in the metatarsophalangeal joints.…”