Accelerometry
Accelerometry (from acceleration = acceleration ) is a method of measuring movement by evaluating the signal supplied by an acceleration sensor. In contrast, the simple actimetry (also: actigraphy) uses mechanical counters and electromechanical sensors for continuous movement registration or video recordings for recording movement sequences.
Accelerometry has numerous areas of application in physics , technology and space travel , but also in many medical disciplines: occupational medicine and physiology , sports biomechanics , sports physiology , medical rehabilitation and even in psychophysiology and some behavioral sciences .
methodology
There are several technical options for measuring movement (see acceleration sensor , sports biomechanics ). Often, miniaturized piezoelectric acceleration sensors made of silicon are used, which convert the pressure fluctuations caused by an acceleration into electrical signals . Small, robust sensors weigh only a few grams and are highly sensitive with good signal resolution . Newer piezoresistive and piezocapacitive sensors deliver a signal that shows not only the acceleration but also the inclination of the sensor (position in relation to gravity ). In the case of a horizontal or vertical position, the direct voltage (DC) components of the signal differ , so the position of the body in space can also be determined. Gyro sensors can also measure angular acceleration . An acceleration sensor only reacts in one dimension with maximum sensitivity, so that two or three sensors must be combined in order to be able to detect movements in a plane or in three-dimensional space. For many purposes, measurements in one or two dimensions (axes) are sufficient, while human movement behavior has to be measured in the three spatial dimensions (planes).
For medical and psychophysiological examinations, small measuring and storage devices (recoder / analyzer systems) are available today for continuous measurement, recording and immediate evaluation in real time (real time analysis), which can even be used under everyday conditions (see ambulatory assessment ) .
For more detailed medical exams, electromyography (EMG) is used to register muscular activity. Video recordings, on the other hand, are suitable when it comes to complicated movement sequences or holistic coordination .
In contrast to the acceleration sensors attached to bodies, the motion detectors are used to detect movements in the immediate vicinity and then automatically switch on lighting or trigger an alarm . Other motion detection techniques were developed to record movements using a camera or bodysuit (full body suit) and to process them with the aid of a computer (see motion measurement or motion tracking , motion capture , animation , film technology ).
Applications
Accelerometry in technical systems
Acceleration or motion measurement with accelerometers has found numerous possible uses, ranging from mechanical engineering , elevator technology , alarm systems , car electronics , inertial navigation , satellite and rocket technology to geophysics and earthquake monitoring (see acceleration sensor ).
Accelerometry in Biology
The analysis of movements in humans and animals is more difficult than in technology. Due to the respective behavioral situation and the individual differences in body structure, there is a high variability in movement patterns . Therefore an optimal examination procedure and an exact secondary signal processing with pattern recognition and with statistical comparisons are necessary.
Accelerometry of human movement behavior
The continuous measurement of body position, movement patterns and physical (motor) activity (motor skills: gross and fine motor skills , locomotor skills , gestures , facial expressions ) is a fundamental task of behavioral science methodology:
- the recognition (detection) of changes in body position, e.g. B. Lying, sitting, standing, and typical movement patterns such as walking, climbing stairs, cycling;
- the distinction between special movements, e.g. B. finger and arm movements, tool use, gestures, head movements such as nodding the head during a conversation;
- the diagnosis and ongoing registration of movement disorders, e.g. B. Tremor of the hand in Parkinson's disease or restless legs syndrome ;
- the monitoring of fitness training and sporting activity, the mobilization of motor disabled patients as well as the probation control of rehabilitation measures in patients with disorders of posture and motor skills;
- the measurement of the 24-hour activity level with the sections physical activity and bed rest (sleep) and the most representative possible recording of movement activity as an index of the metabolism (energy expenditure).
In addition to continuous activity measurement (actimetry), accelerometry enables the reliable detection of body position, movement patterns and movement disorders. These advances in motion measurement were achieved through the development of new piezoresistive acceleration sensors, which also show their position in relation to the gravitational axis, through miniaturized digital recorders for multi-channel recordings and through modern methods of signal filtering, amplitude-frequency analysis and statistical analysis ( pattern recognition ). With suitable placement, a small sensor system with three axes is sufficient for the dimensions of the room to reliably detect the most important differences in position and movement, with only a few percent misclassifications occurring. Additional sensors are required to detect special activities or movement disorders ( multiple accelerometry ). The methodology can be individually adapted to the specific motor symptoms and the individual movement style through a test registration (calibration) and through statistical comparison with the movement patterns recorded later. Accelerometry is a well-established method for which there are numerous areas of application in psychology and medicine.
literature
- Hans BJBussmann, Ulrich Ebner-Priemer, Jochen Fahrenberg: Ambulatory behavior monitoring: Progress in measurement of activity, posture, and specific motion patterns in daily life . In: European Psychologist, 2009, Volume 14, 142–152.
- Kong Y. Chen, David R. Bassett: The technology of accelerometry-based activity monitors: Current and future . In: Medicine and Science in Sports and Exercise , 2005, Volume 37, 490-500.
- Jochen Fahrenberg, Rainer Leonhart, Friedrich Foerster: Everyday psychology with hand-held PC and physiological measuring system. Huber, Bern 2002, ISBN 3-456-83818-2 .
- Friedrich Foerster: Assessment of posture, motion, and hand tremor by calibrated accelerometry . In Jochen Fahrenberg, Michael Myrtek (Eds.): Progress in ambulatory assessment. Hogrefe & Huber, Seattle, WA 2001, ISBN 0-88937-225-X , pp. 233-256.
- Friedrich Foerster, Jochen Fahrenberg: Motion pattern and posture: Correctly assessed by calibrated accelerometers . In: Behavior Research Methods, Instruments and Computers , 2000, Volume 32, 450-457.
- Merryn J. Mathie, Branko G. Celler, Nigel H. Lovell, Adelle CF Coster: Classification of basic daily movements using a triaxial accelerometer . In: Medical and Biological Engineering and Computing , 2004, Volume 42, 679-687.
- Warren W. Tryon: Activity measurement . In Michel Hersen (Ed.). Clinician's handbook of adult behavioral assessment. Academic Press, New York 2006, ISBN 0-12-343013-5 , pp. 85-120.