A goal of this study is to test and compare three LDAs. Two of these LDA’s were designed and developed at the University of Utah. The Utah Exoskeleton (Torsion Spring), shown on the left, and The Utah Exoskeleton (Bending Member Device) shown below, store energy while bending and then returns energy through shoulder straps (similar to a normal backpack) to generate a lifting torque about the hips.The lift assist device in the first figure works similarly to the device in Figure 2, but through a different method. Torsion springs are fixed between the upper body attachment (backpack), and the lower body attachments (thigh panels). These torsion springs also provide resistance to bending the body by absorbing part of the energy. This energy is used to support the body. The springs have an adjustable pre-load so the user can choose how much assistance to receive from the device. A hard stop prevents the user from over extending while using this device.
The lift assist device shown in Figure 2 utilizes a bending member mechanism for storing and releasing energy. The upper segment attaches to the user’s torso much like a backpack. The lower two attachments connect to the user’s thighs with quick-release straps. As the user’s body bends, some energy is stored in the orange fiberglass members, and the energy is released as the user straightens the body. So the device resists bending, but assists while straightening the body or lifting. It also helps to support the body when the body is in a motionless bent posture. The sliders placed on both of the leg attachments allow the user a more comfortable range of motion which may be helpful when walking. The device also resists overextension as a safety feature.
The Springzback™ (Figure 3) is a commercially available device that provides relief to the back while bending and lifting. A special belt is worn by the user and the device clips to the belt on the anterior side of the pelvis.
The lift assist device in Figure 3 is a commercial device that attaches to the front of the body with two straps that wrap behind the body. The device utilizes an adjustable fluid compression mechanism to provide resistance when bending the body. Similar to other designs, this resistance reduces some of the force in the muscles while lifting. Like the other two lift assist devices described above, this mechanism allows each leg to move independent of the other. But unlike the other two devices, this design includes a hinge which allows for abduction and adduction of the legs (or moving the legs from side to side).
This study will investigate the biomechanical forces that a user will experience while performing lifting exercises and while maintaining multiple static positions with the aide of a lift assist device. This will be accomplished by modeling the body in the sagittal (side view) plane. Reflective markers will be placed at predetermined anatomical locations to track position, velocity and accelerations of the body. The study will also include data acquisition of the activity level of the erector spinae muscles (muscles of the back involved in lifting/bending) via Electromyography (EMG). Finally, each test subject will be given a questionnaire with which information regarding personal comfort and any useful user feedback may be obtained. The information acquired in this study will be used in future designs of assisted lift devices.