The Motion of Body Center of Mass During Walking: A Review Oriented to Clinical Applications

Abstract

Human walking is usually conceived as the cyclic rotation of the limbs. The goal of lower-limb movements, however, is the forward translation of the body system, which can be mechanically represented by its center of mass (CoM). Lower limbs act as struts of an inverted pendulum, allowing minimization of muscle work, from infancy to old age. The plantar flexors of the trailing limbs have been identified as the main engines of CoM propulsion. Motion of the CoM can be investigated through refined techniques, but research has been focused on the fields of human and animal physiology rather than clinical medicine. Alterations in CoM motion could reveal motor impairments that are not detectable by clinical observation. The study of the three-dimensional trajectory of the CoM motion represents a clinical frontier. After adjusting for displacement due to the average forward speed, the trajectory assumes a figure-eight shape (dubbed the “bow-tie”) with a perimeter about 18 cm long. Its lateral size decreases with walking velocity, thus ensuring dynamic stability. Lateral redirection appears as a critical phase of the step, requiring precise muscle sequencing. The shape and size of the “bow-tie” as functions of dynamically equivalent velocities do not change from child to adulthood, despite anatomical growth. The trajectory of the CoM thus appears to be a promising summary index of both balance and the neural maturation of walking. In asymmetric gaits, the affected lower limb avoids muscle work by pivoting almost passively, but extra work is required from the unaffected side during the next step, in order to keep the body system in motion. Generally, the average work to transport the CoM across a stride remains normal. In more demanding conditions, such as walking faster or uphill, the affected limb can actually provide more work; however, the unaffected limb also provides more work and asymmetry between the steps persists. This learned or acquired asymmetry is a formerly unsuspected challenge to rehabilitation attempts to restore symmetry. Techniques of selective loading of the affected side, which include constraining the motion of the unaffected limb or forcing the use of the affected limb on split-belt treadmills which impose a different velocity and power to either limb, are now under scrutiny.

Latest Research Trends in Gait Analysis Using Wearable Sensors and Machine Learning: A Systematic Review

“…Gait is the periodic movement of hands and feet [53]. Different gait patterns are distinguished by differences in velocity, limb movements, force, and ground contact duration.…”

Mechanical and energetic determinants of impaired gait following stroke: segmental work and pendular energy transduction during treadmill walking

“…Human walking can be modeled as an inverted pendulum. In this model, the body center of mass (BCoM), potential energy (Ep) and kinetic energy (Ek) are in a continuous exchange to minimize mechanical work and energy production (Gordon et al, 2009;Saibene and Minetti, 2003;Tesio and Rota, 2019). When this optimal walking mechanic is changed, abnormal trajectories of the BCoM and body segments may lead to greater mechanical work production or reduced energy exchange, ultimately influencing the energy cost of locomotion (Massaad et al, 2007).…”

Kinematic Gait Adjustments to Virtual Environments on Different Surface Conditions: Do Treadmill and Over-Ground Walking Exhibit Different Adaptations to Passive Virtual Immersion?

“…Along these lines, it has been described that clearance of obstacles can be modified by the obstacles' characteristics. For instance, pedestrians modify their clearance when crossing an aperture formed by two people as opposed to poles [ 38 ] or when avoiding human-like avatars compared to inanimate objects immersed in VREs [ 39 ]. However, in the later trials (C7), participants began anticipating the VRE accurately, and thus only slight adjustments were needed to avoid collisions with the virtual people (Figures 3(b) and 3(d) ).…”

“…It has been well described that the motion of the COM itself is a constant target of neural control which could be used to describe gait and balance performance [ 38 ]. Additionally, relating the COM motion to the segmental kinematic perspective allows the understanding of adaptative mechanisms during gait [ 38 ]. In this context, both COM kinematic outcome measures reported in this study were considered as kinematic markers of the level of interaction of the participants with the VREs.…”