Motion pattern and posture: Correctly assessed by calibrated accelerometers

Abstract

Basic motion patterns and posture can be distinguished by multichannel accelerometry, as recently shown. A refinement of this method appeared to be desirable to further increase its effectiveness, especially to distinguish walking and climbing stairs, and body rotation during sleep. Recordings were made of 31subjects, according to a standard protocol comprising 13motions and postures. This recording was repeated three times with appropriate permutation. Five uni-axial sensors and three sites of placement (sternum with three axes, right and left thigh) were selected. A hierarchical classification strategy used a standard protocol (i. e., individual reference patterns) to distinguish subtypes of moving behaviors and posture. The analysis method of the actometer signals reliably detected 13 different postural and activity conditions (only 3.2%misclassifications). Aminimum set of sensors can be found for a given application; for example, a two-sensor configuration would clearly suffice to differentiate between four basic classes (sitting, standing, lying, moving) in ambulatory monitoring.The assessment of movement and posture, and, generally, the kinematic analysis of behavior, has greatly profited from the progress made in sensor technology and advanced methods in signal analysis. The conventional method made use of wrist-worn actometers, tilt-switch transducers, mechanical pedometers, piezoceramic sensors, and other electronic devices to register movements. Actometer devices are suitable for many applications, and actometers are less expensive than the infrared-light method ofkinematic analysis, easier to apply than recordings of the electromyogram, and more convenient than videotape analysis. The measurement of activity in psychology and medicine was reviewed by Tryon (1991; see also H. Bussmann, 1998).Recent progress in the assessment of movement and posture resulted from three developments: First, the wide bandwidth of new piezoresistive (e.g., ICSensor Model 3031, Analog Devices ADXL202) and piezocapacitive sensors have paved the way for the development ofa new method with calibrated actometers. The DC signal output (i.e., signal output <0.5 Hz) allows the assessment of change in position in relation to the gravitational axis (i.e., inclination in degrees). The AC signal output >0.5 Hz in terms of the gravitation-that is, g (or milli-g)--represents acceleration along the sensitive axis of the device; second, the development of pocket-sized digital data recorders has especially facilitated multichannel

Valoración de la capacidad funcional en el ámbito domiciliario y en la clínica: Nuevas posibilidades de aplicación de la acelerometría para la valoración de la marcha, equilibrio y potencia muscular en personas mayores

“…Es conocido que, la mayoría de los movimientos humanos ocurren entre 0,3 y 3,5 Hz 39 . Por tanto, la mayoría de investigadores usan filtros que cortan la señal entre 0,1 y 0,5 para separar cada componente de la señal estática y la señal debida al movimiento 36,40,41 .…”

“…La aceleración aumenta en magnitud de la cabeza a los tobillos. Correr produce las aceleraciones mayores en la dirección vertical de 8,1 -12 g en el tobillo [35][36][37][38][39][40][41][42][43][44] , hasta 5,0g en la parte lumbar [35][36][37][38][39][40][41][42][43][44] y hasta 4,0 en la cabeza 44 . Las aceleraciones del tronco en el eje vertical que se han obtenido durante la marcha abarcan el rango -0,3 a 0,8 g, mientras que en dirección horizontal medido en la zona lumbar el rango va de -0,3 a 0,4 g y de -0,2 a 0,2 en la cabeza 45 .…”

“…Se pueden medir durante la marcha normal con las aceleraciones de la cintura, muslo o talón parámetros como tiempo de paso, de ciclo y simetría de zancada 34,41,53 . La componente vertical de la aceleración del tronco es lo más importante en la evaluación de la marcha [40][41] . Ésta es la componente más sensible a la presencia de trastornos en la marcha, y de la cual se pueden obtener más parámetros del ciclo de la marcha 53 .…”

A system for monitoring posture and physical activity using accelerometers

“…Accelerometers have been used to measure posture [6,7], mobility and gait [4,10] and metabolic energy expenditure [8]. These measurements indicate the amount of time that a patient spends engaged in various physical activities such as standing, sitting and walking as well as the amount of energy used during the day.…”

“…Accelerometers have been used for several decades to monitor body movement in subjects [4,5], and, more recently, for determining posture [6,7]. Technological advances have allowed the development of miniature, low powered, wireless accelerometer devices that are suitable for use by "free-living" subjects over prolonged periods [8].…”