Former Undergraduate Researcher Stevens Institute of Technology Lynnwood, Washington, United States
Introduction:: Sit-to-stand (STS) is a fundamental function of everyday life but can cause injury and lack of independence for those unable to perform the movement due to neuromuscular diseases. The movement involves transitioning from a seated position to a standing position without the loss of balance. Healthy adults perform on average 60 (±22) STSs per day [1]. Performing a STS is also a part of the timed up-and-go test (TUG) that is performed to assess the lower extremity function, mobility, and fall risk in patients [2]. Age and disease can impact the execution of the STS movement, as a decrease in balance and muscle strength can increase the need for intervention during a STS [3,5]. With diseases that affect balance and coordination, such as stroke and Parkinson's disease, patients may perform distorted or wrong motions during a STS, which could increase their chance of falling. A previous study has shown that 37.2% of falls in stroke patients occur during the STS movement [4,5]. The STS movement phases have been categorized using kinematics [3] and electromyography [6], but there is little research on the pressure distribution on the foot during the movement. This study aims to further categorize the phases of the STS movement through foot pressure mapping technology, focusing on the pressure distribution and forces experienced on the feet throughout the movement.
Materials and Methods:: The F-Scan Pressure Measurement Foot System was used to collect foot pressure mappings of 2 female subjects. The F-Scan sensors were taped to the ground in front of a stool. The F-Scan sensors were calibrated individually to the subjects’ body weights utilizing F-Scan’s calibration protocol. The subjects were asked to remove their shoes and sit on the stool, adjusted for their feet to fully touch the ground while fully seated. The subjects were asked to perform the STS movement from a fully sitting to a fully standing position, with their feet placed on the sensors throughout the movement. They were asked to perform the STS movement 5 times.
Results, Conclusions, and Discussions:: Pressure mapping of both feet was collected to analyze the pressure distribution, force-time profiles, and center of force (COF)-time profiles of STS trials. Observations include an average high concentration of pressure within the heels and balls of the feet, as well as variable force and COF position during the movement.
Analyzing videos of the foot pressure mapping compared to the force-time profiles during the STS movement informs how force is distributed over the foot throughout the STS movement. As such, the trends of the foot pressure distribution can be paired with the phases of the STS movement, with the phases of the STS based on the foot pressure mapping categorized as such: Phase 0 - Fully Sitting, Phase 1 - Trunk Tilt, Phase 2 - Thighs Off, Phase 3 - Rising, and Phase 4 - Full Stand.
Once these phases of foot pressure were identified, the phases could be synchronized with the force-time profile of the STS movement. As seen with the foot pressure mapping, Phase 1 has a rapid and high increase in pressure leading to the pressure peaking at Phase 2. Phase 3 shows variability in force that happens as someone is getting up from a movement and as the pressure distribution moves throughout the foot. Phase 4 shows that the changes in the forces stabilize once one is fully standing. The distribution of pressure on the foot during the STS movement is high at the heel and ball of the foot, with pressure moving from heel to ball until pressure is distributed over the whole foot. This is likely due to the center of mass moving anterior as the person moves from a sitting to a standing position.
Since STS is a transition movement, there is a high fall risk as the COF changes anterior/posterior, and force distribution is not equal over the foot. Those with distal muscle weakness and injury may not be able to perform the necessary forces to stand. Therefore this data can help inform physical therapists in the rehabilitation of patients having difficulty performing the STS movement.
Acknowledgements (Optional): : Thank you to Dr. Sally Shady from Stevens Institute of Technology for encouraging me to write this abstract!
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