The HGN Lab for Bionic Engineering is equipped with three dedicated labs for motion analysis. The first space is dedicated to gait analysis and includes an “in-ground” Bertec instrumented treadmill (with instrumented handrails), Vicon cameras, and overhead support. The second space is dedicated to ergonomics studies and includes Bertec force plates, Vicon cameras, and overhead support. The third space is dedicated to ambulation and functional mobility and includes an ambulation circuit with an instrumented staircase, ramp, elevated walkways, stairs, force plates, Vicon cameras, and Safe-gait active weight support system. Additional equipment includes the full-body Xsens Awinda inertial motion system, Delsys 16-channels electromyography system, and Cosmed K5 for indirect calorimetry. Below are some examples of biomechanics studies performed using this equipment.
Exoskeleton Studies
Ankle Exoskeleton
The ankle exoskeleton project aims to assist individuals with ankle weakness resulting from hemiparesis following a stroke. The Utah Ankle Exoskeleton is lightweight and fully integrated, with high torque density. Preliminary results suggest that ankle exoskeleton assistance can lead to more normative kinematics and increased foot clearance, reducing compensatory movements and fall risk.
Two-Degree-of-Freedom Hip Exoskeleton
In the 2-DOF Hip Exoskeleton study, we explore the impact of both frontal and sagittal plane torques generated by a portable hip exoskeleton on individuals with hemiparesis. Our central hypothesis is that hip abduction torque will increase step width and margin of stability, while sagittal plane torques will increase propulsive force. To test this hypothesis, we measured the foot placement and full body kinematics and kinetics of individuals with hemiparesis while receiving frontal and sagittal plane hip torques applied by an exoskeleton and compared these results to the same subjects walking without the exoskeleton. We tested multiple levels of hip abduction torque to closely study the relationship between frontal plane torque and step width, margin of stability, and propulsive force. Quantifying the effect of frontal plane assistance on gait stability and propulsion in individuals with hemiparesis could lead to the development of effective interventions, such as portable exoskeletons, that provide immediate benefits for this population by increasing their mobility and quality of life.
Utah Knee Exoskeleton
The Utah Knee Exoskeleton is fully enclosed, lightweight, and can provide biological levels of knee torque. The goal of this project is to improve the mobility of individuals with spinal cord injuries during daily ambulation activities, including walking, stair ascent and descent, and ramp ascent and descent.
Knee Exoskeleton during Sit-to-Stand Transitions
In this study, we asked 8 individuals with hemiparesis to stand up and sit down with our first-generation knee exoskeleton using direct myoelectric control. We recorded muscle effort and full-body motion capture. The knee exoskeleton improved stand-up speed, symmetry, and muscle effort. Read the full paper here.
Hip Exoskeleton Improves Above-Knee Amputee Metabolic Cost
In this study, we used assistive wearable robotics in a unique way - we used a bilateral hip exoskeleton to improve the metabolic cost of walking in above-knee amputees, who walked on a treadmill with their passive prosthetic knee and ankle. We found a 15.6% improvement in metabolic cost, which is the equivalent of removing a 12-kg backpack from a non-amputee individual. Check out the full paper here.
Prosthesis Studies
Knee Prosthesis - Stance Knee Flexion
Stance Knee Flexion (SKF) plays a critical role in biological gait by absorbing impact and returning energy to support forward motion. Above-knee amputees typically lose this functionality, as passive prostheses cannot generate the positive power needed for physiological SKF. In this study, individuals with unilateral above-knee limb loss walked with an active knee prosthesis under two conditions: a stiff, high-impedance mode and a control mode designed to replicate physiological SKF.
When SKF was enabled, the prosthesis closely matched biological knee behavior—flexing during early stance, generating appropriate extension torque, and absorbing and returning energy similar to a natural limb. Importantly, providing physiological SKF reduced residual hip extension torque by 36%, indicating a meaningful decrease in compensatory effort.
Knee Prosthesis - Ramp Descent
Walking down slopes is a common activity where many people experience knee pain, and this is especially true for transfemoral amputees who have an increased risk of developing knee osteoarthritis. Risk of knee osteoarthritis has been linked to elevated knee contact forces, often seen in transfemoral amputees. In an effort to alleviate pain and symptoms of osteoarthritis, we are investigating the effect of modulating prosthetic knee resistive torque through damping on knee contact forces. After collecting motion capture data for various damping levels, we used OpenSim to model the musculoskeletal dynamics for each condition. Using static optimization to solve for predicted muscle force, we estimated the resulting knee contact force for each test condition. Our results suggest that an intermediate level of damping minimizes knee contact force, potentially leading to reduced risk of pain and osteoarthritis.
Knee Prosthesis - Metabolic Cost
Individuals with a transfemoral amputation typically experience an increase in the metabolic cost of walking post-amputation. This is most likely due to the prescribed prostheses being unable to inject positive energy during the gait cycle, requiring the intact joints to perform compensatory movements to successfully propel the body forward. In this study, 8 individuals with a transfemoral amputation walked on a treadmill for 6 minutes at a self-selected speed with both their prescribed prosthesis and the Utah Bionic Knee. Both metabolic and biomechanical measurements were taken. From this study, we saw, on average, a 15.5% reduction in the metabolic cost of walking with the Utah Bionic Knee. Secondly, we saw a 15.6% reduction in the positive biological joint work of walking with the Utah Bionic Knee.
Knee-Ankle Prosthesis - Stair Ascent and Descent
Stair ambulation presents significant challenges for prosthesis users due to the coordination required between sound and prosthetic limb movement and the high energy demands of the knee and ankle joints. Traditional passive prostheses, which cannot provide positive energy or control negative energy, require prosthesis users to compensate with their biological joints, which may lead to further mobility impairments. The objective of this study is to assess the relationship between coordinated prosthetic energy injection and sound limb burden: in stair ascent, to characterize the relationship between positive energy modulation via torque provided by an active prosthetic knee and work done by biological joints; in stair descent, to assess the effect of negative energy modulation via physiological movement at an active ankle prosthesis on sound-side knee joint contact force.
Salt Lake One Ankle Prosthesis
The Salt Lake One powered ankle project focuses on analyzing and replicating the natural behavior of the ankle throughout the gait cycle. This includes studying joint kinematics, ground‐reaction forces, and the timing and magnitude of muscle contractions that drive normal ankle mechanics. We are developing the powered ankle to replicate these biomechanical patterns, thereby restoring efficient push-off, enhancing stability, and creating a more natural and symmetrical walking experience for the user.
Knee-Ankle Prosthesis - Sit-to-Stand Transitions
Stand up and sit down are essential activities of daily living which are prerequisites to independence. These activities are also strenuous, requiring large amounts of knee extension torque. In this study, we asked above-knee amputees to perform stand-up and sit-down with our powered knee-ankle prosthesis providing 8 different levels of stand-up assistance. We performed full-body motion capture. We found that the powered prosthesis improved symmetry and muscle effort during both stand-up and sit-down. Read the open-access papers here: stand-up, sit-down. We also published an open-source dataset of the passive prosthesis trials: check out the dataset and the paper that describes it.
Other Studies
Bump'em Perturbation Study
The Bump-Em perturbation study aims to analyze the biomechanical responses of above-knee amputees to controlled mediolateral perturbations and compare amputee and able-bodied balance control strategies. To accomplish this, we asked 8 above-knee amputees and 8 non-amputee controls to walk on a treadmill while a “Bump’em” waist-cable system applied medial/lateral pulling perturbations at different times in the gait cycle. We hypothesize that amputees will experience greater instability from perturbations than able-bodied subjects due to limitations with their prosthesis and residual limb, and this difficulty will be exacerbated by a directional effect in which balance is worse when pulled toward the prosthesis side, leading to longer recovery times and more recovery steps. The information gained in this study is necessary to enable the development of new assistive devices, controllers, and rehabilitation strategies to improve the walking balance of above-knee amputees. This study could inform control strategies for powered prostheses and exoskeletons to improve balance recovery responses in above-knee amputees, improving mobility and lowering fall risk.