Optimum Handle Location for the Hand-Assisted Sit-to-Stand Transition: A Tool

Abstract

Background: The aging process contributes to the decline in physical capacity that leads to loss of independence in performing life activities. Immobility and instability are the most significant predictors and indicators of physical disability and dependence. As a result, a variety of assistive devices exist to address immobility and instability in older adults, including walkers, canes, crutches, wheelchairs and handrails. Sit-to-stand (STS) transitions are the most common transitions in daily mobility activities. The ability to perform STS transitions successfully is therefore one of the most important activities to focus attention on. As a result of physical deterioration, older adults will sooner or later be faced with their physical limitations, and in particular, will not be able to provide enough torque at critical body joints to make the STS transition. Aim: This paper suggests employing two-arm assistance using two handles located symmetrically in the body’s sagittal plane. During the aging process, people are faced with varying levels of muscle deterioration and body constraints and consequently require different levels of assistance to complete the transition successfully. This paper aims to develop a tool to find the optimum handle location for people based on their body constraints to reduce knee torque (identified as the critical joint in the STS transition). These findings are also used to measure the effects of assistive device handle position on the biomechanics of the two-arm assisted STS transition. Methods: For this purpose, a theoretical tool was developed by integrating human body kinetics with a multi-objective genetic algorithm to find the optimum hand force required at the seat-off point for a set of potential handle locations. The tool was set to achieve the minimum knee torque within the defined body constraints and assumptions. In line with the physics of the STS transition, the “seat-off point”, when subjects lose their seat support, was chosen as the most challenging point of the task. This was coupled with the “nose over toes” posture recommended to older adults by occupational therapists. Results and Discussion: The schematic of the developed tool shows that the best handle locations requiring the minimum torques at the body joints are positioned in handle zone 2, where the handles are placed vertically above the knee and below the hip joints and horizontally located ahead of the hip and behind the knee joints. Within this handle zone, both components of the hand forces (vertical downward and horizontal backward) provide assisting torque to all the body joints and consequently reduce the torques required at body joints.