Chair rise transfer detection and analysis using a pendant sensor: An algorithm for fall risk assessment in older people

Falls result in substantial disability, morbidity, and mortality among older people. Early detection of fall risks and timely intervention can prevent falls and injuries due to falls. Simple field tests, such as repeated chair rise, are used in clinical assessment of fall risks in older people. Development of on-body sensors introduces potential beneficial alternatives for traditional clinical methods. In this article, we present a pendant sensor based chair rise detection and analysis algorithm for fall risk assessment in older people. The recall and the precision of the transfer detection were 85% and 87% in standard protocol, and 61% and 89% in daily life activities. Estimation errors of chair rise performance indicators: duration, maximum acceleration, peak power and maximum jerk were tested in over 800 transfers. Median estimation error in transfer peak power ranged from 1.9% to 4.6% in various tests. Among all the performance indicators, maximum acceleration had the lowest median estimation error of 0% and duration had the highest median estimation error of 24% over all tests. The developed algorithm might be feasible for continuous fall risk assessment in older people.

I. Introduction

Approximately one in three people over the age of 65 fall each year, resulting in significant physical and emotional cost on the individual and their family[1]. Older people suffering from serious injuries due to falls may lose their mobility, which has a dramatic impact on the quality of their lives[2]. An early detection of increased fall risk may allow timely interventions and reduce falls or injuries resulting from falls significantly[3]. Chair rise performance is influenced by the leg strength and power and measured as an indicator of fall risk status in older people[4], [5]. Functional tests, such as Timed-Up-Go (TUG), Five-Times-Sit-to-Stand and single chair rise test are usually incorporated in clinical fall risk assessments [6]–[8]. However, the aforementioned functional tests are only applied in controlled setups under the supervision of clinical professionals. Completion time and subjective evaluation of the difficulty when completing the test are the performance indicators. The development of on-body sensors facilitates studies in fall risk assessments beyond traditional clinical setup and measurements[6], [9]–[11]. Sensor-based chair rise assessment provides additional objective performance indicators besides the completion time. For example, peak power of a sit-to-stand (STS) transfer is measured using body-fixed sensors consisting of an accelerometer, a gyroscope and a magnetometer[9]. Fair to excellent agreements of transfer peak power measured with a standard method using force-plate and body-fixed sensors is presented. Other STS transfer performance indicators obtained from on-body sensors reported in previous studies include duration, velocity, maximum jerk, maximum acceleration and frequency features of accelerations [10]–[12]. The performance of the chair rise transfer can be measured with one or multiple sensors fixed on the body. For example, in study [12], STS timing is determined by a pair of sensors attached to the chest and the thigh. In [10], [11], [13], sensors fixed at the chest, one side of the hip and the center of mass (COM) are used to measure maximum acceleration, jerk and duration. To better understand the progression of fall risk and provide accurate assessment, prospective longitudinal studies in community settings are needed[2]. A low-cost easy-to-use fall risk assessment tool is desirable from this research perspective.