Estimation of the body center of mass velocity during gait of people with transfemoral amputation from force plate data integration

Quantification of push-off and collision work during step-to-step transition in amputees walking at self-selected speed: Effect of amputation level

Maintaining forward walking during human locomotion requires mechanical joint work, mainly provided by the ankle-foot in non-amputees. In lower-limb amputees, their metabolic overconsumption is generally attributed to reduced propulsion. However, it remains unclear how altered walking patterns resulting from amputation affect energy exchange. The purpose of this retrospective study was to investigate the impact of self-selected walking speed (SSWS) on mechanical works generated by the ankle-foot and by the entire lower limbs depending on the level of amputation. 155 participants, including 47 non-amputees (NAs), 40 unilateral transtibial amputees (TTs) and 68 unilateral transfemoral amputees (TFs), walked at their SSWS. Positive push-off work done by the trailing limb (WStS+) and its associated ankle-foot (Wankle-foot+), as well as negative collision work done by the leading limb (WStS-) were analysed during the transition from prosthetic limb to contralateral limb. An ANCOVA was performed to assess the effect of amputation level on mechanical works, while controlling for SSWS effect. After adjusting for SSWS, NAs produce more push-off work with both their biological ankle-foot and trailing limb than amputees do on prosthetic side. Using the same type of prosthetic feet, TTs and TFs can generate the same amount of prosthetic Wankle-foot+, while prosthetic WStS+ is significantly higher for TTs and remains constant with SSWS for TFs. Surprisingly and contrary to theoretical expectations, the lack of propulsion at TFs' prosthetic limb did not affect their contralateral WStS-, for which a difference is significant only between NAs and TTs. Further studies should investigate the relationship between the TFs' inability to increase prosthetic limb push-off work and metabolic expenditure.

Comparison of ground reaction force and marker-based methods to estimate mediolateral center of mass displacement and margins of stability during walking

Dynamic balance control during human walking can be described by the distance between the mediolateral (ML) extrapolated center of mass (XCoM) position and the base of support, the margin of stability (MoS). The ML center of mass (CoM) position during treadmill walking can be estimated based on kinematic data (marker-based method) and a combination of ground reaction forces and center of pressure positions (GRF-based method). Here, we compare a GRF-based method with a full-body marker-based method for estimating the ML CoM, ML XCoM and ML MoS. Fifteen healthy adults walked on a dual-belt treadmill at comfortable walking speed for three minutes. Kinetic and kinematic data were collected and analyzed using a GRF-based and marker-based method to compare the ML CoM, ML XCoM and ML MoS. High correlation coefficients (r > 0.98) and small differences (Root Mean Square Difference < 0.0072 m) in ML CoM and ML XCoM were found between the GRF-based and marker-based methods. The GRF-based method resulted in larger ML XCoM excursion (0.0118 ± 0.0074 m) and smaller ML MoS values (0.0062 ± 0.0028 m) than the marker-based method, but these differences were consistent across participants. In conclusion, the GRF-based method is a valid method to determine the ML CoM, XCoM and MoS. One should be aware of higher ML XCoM and smaller ML MoS values in the GRF-based method when comparing absolute values between studies. The GRF-based method strongly reduces measurement times and can be used to provide real-time CoM-CoP feedback during treadmill gait training.

Determination of the center of mass in a heterogeneous population of dogs

The center of mass (CoM) is the location in a body where mass distribution is balanced. It has a fundamental role in balance and motion which has been poorly described in the dog. The objective of this study was to estimate the variance of the center of mass (CoM) in a heterogeneous population of client-owned dogs and to describe the relationship between CoM, subject morphometrics and an inertial measurement unit (IMU) box positioned ventrally on a neck collar. A single force platform and a reaction board were used to determine CoM in the transverse, sagittal and dorsal planes in thirty-one healthy adult dogs. A series of morphometric measurements were acquired with each dog standing, including distances relative to an IMU box positioned ventrally on a neck collar. Mean transverse plane CoM was 48% the distance from ischium to the IMU box, near the xiphoid process. Mean sagittal place CoM was 59% the width of the chest on the left side. Mean dorsal plane CoM was 41% the distance from the most dorsal to the most ventral aspect of the body. Dog length was the primary variable required to maximize the relationship between three-dimensional CoM and identifiable variables measured. A CoM based normalization procedure should be considered to normalize mass or motion based outcome measure output (e.g., ground reaction forces, vector acceleration) in a heterogeneous population of dogs. Future research will be needed to determine if CoM-based normalization procedures reduce variance in outcome measures affected by subject morphometrics.

Characterizing the Gait of People With Different Types of Amputation and Prosthetic Components Through Multimodal Measurements: A Methodological Perspective

Prosthetic gait implies the use of compensatory motor strategies, including alterations in gait biomechanics and adaptations in the neural control mechanisms adopted by the central nervous system. Despite the constant technological advancements in prostheses design that led to a reduction in compensatory movements and an increased acceptance by the users, a deep comprehension of the numerous factors that influence prosthetic gait is still needed. The quantitative prosthetic gait analysis is an essential step in the development of new and ergonomic devices and to optimize the rehabilitation therapies. Nevertheless, the assessment of prosthetic gait is still carried out by a heterogeneous variety of methodologies, and this limits the comparison of results from different studies, complicating the definition of shared and well-accepted guidelines among clinicians, therapists, physicians, and engineers. This perspective article starts from the results of a project funded by the Italian Worker's Compensation Authority (INAIL) that led to the generation of an extended dataset of measurements involving kinematic, kinetic, and electrophysiological recordings in subjects with different types of amputation and prosthetic components. By encompassing different studies published along the project activities, we discuss the specific information that can be extracted by different kinds of measurements, and we here provide a methodological perspective related to multimodal prosthetic gait assessment, highlighting how, for designing improved prostheses and more effective therapies for patients, it is of critical importance to analyze movement neural control and its mechanical actuation as a whole, without limiting the focus to one specific aspect.