Actometer

An actometer (also known as an actigraph ) is a measuring device for recording the movement activity of a subject . It is worn like a wrist watch on the wrist or on the ankle. The measurement is usually carried out over a longer period of time (a few weeks) in which the device is worn 24 hours a day.

Modern actometers are light, slightly larger than a wristwatch, and store the data on changes in position and acceleration values on a chip that can be read out on the computer. In some cases, actometers also offer the option of using additional sensors to measure additional parameters such as the light intensity in the subject's surroundings, the ambient and body temperature, and thus to obtain additional information for the evaluation.

The profile of the intensity of movement as a diagram of frequency and intensity in relation to the time axis is called the “actogram”. The process of data acquisition and evaluation is " actigraphy ".

functionality

Actometers are accelerometer-based devices that continuously capture, digitize, and record movement in one, two, or three dimensions. The storage space for the amount of data and the performance of the battery make measurements over several weeks and months possible without any problems. The piezoceramic accelerometers emit a voltage, while the determined forces stand for a positive or negative acceleration. If the acceleration is constant, there is no voltage after a short time, as in the absence of movement. The fact that the extremities are connected to the torso means that constant acceleration in a single direction does not occur over a long period of time and these accelerometers can be used here without any problems. Every change in direction generates acceleration again.

With regard to the location of the attachment, it should be noted that the device takes into account the acceleration that acts on itself. An actometer worn on the left wrist does not take into account movements of the right arm or legs. Depending on the question, one should pay attention to this fact. In sleep medicine measurements, the wrist is always assumed to be the place of attachment.

With regard to the length and the valuation of an epoch, autocorrelation must be considered. Anyone who walks or sits for a second in a short epoch of length will most likely still be on the move or sit in the next epoch. This consistency is no longer given when storing or displaying in longer periods. One must also consider how a very brief violent movement is to be interpreted in the representation of an epoch.

For the field of sport it is important that newer devices can recognize and record not only the presence of movement (acceleration) but also the intensity.

When it comes to questions relating to sleep medicine, the very high correlation between measurements using the actometer and polysomnography with regard to values such as sleep duration must not be overestimated. What is not common in healthy people can happen in patients with sleep disorders. Several very short episodes of complete waking up and subsequent falling asleep without much exercise that were not taken into account do not change the total so much for a sleep duration of about eight hours, but prevent the rest of the sleep.

Areas of application

Use in sleep medicine

In sleep medicine , actigraphy is an aid in the investigation of certain sleep disorders and is often used in addition to a sleep diary kept individually by the patient to supplement and objectify the recording of sleep-wake times. A differentiation of sleep with regard to sleep stages or awakening disorders, which is necessary for the actual diagnosis, is not possible. The actigraphy shows a sleep pattern in the sense of a circadian pattern of sleep and wakefulness over several sleep cycles.

Application in sleep research

In the sleep research , the fact is used that the collection of data does not take place localized and is possible in the familiar environment of the subjects. The computer-aided, less labor-intensive evaluation enables larger groups to be examined and examinations over a longer period of time with manageable effort. As long as the parameters to be recorded and the achievable accuracy are sufficient for the respective question, the environment of a sleep laboratory can be dispensed with.

Application in the other areas

Detection of hyperactivity , to measure the degree of hyperactivity, the movement values of average active people are usually used for comparison.
Use in research in the field of chronobiology
Use in competitive sports

Individual evidence

↑ Product example ( Memento from April 22, 2010 in the Internet Archive )
^ ^A ^b Warren W. Tryon: Behavioral Sport Psychology . Springer, New York 2011, ISBN 978-1-4614-0069-1 , Actigraphy: The Ambulatory Measurement of Physical Activity, p. 25-41 , doi : 10.1007 / 978-1-4614-0070-7_2 (English).
↑ S3 guideline for non-restful sleep / sleep disorders of the German Society for Sleep Research and Sleep Medicine (DGSM). In: AWMF online (as of 2009)
↑ ^a ^b Timothy Morgenthaler et al., Standards of Practice Committee, American Academy of Sleep Medicine: Practice Parameters for the Use of Actigraphy in the Assessment of Sleep and Sleep Disorders: An Update for 2007 . In: Sleep . tape 30 , no. 4 , 2007, p. 519-529 , PMID 17520797 (English).

[1] Product example ( Memento from April 22, 2010 in the Internet Archive )

[Tryon-2] A ^b Warren W. Tryon: Behavioral Sport Psychology . Springer, New York 2011, ISBN 978-1-4614-0069-1 , Actigraphy: The Ambulatory Measurement of Physical Activity, p. 25-41 , doi : 10.1007 / 978-1-4614-0070-7_2 (English).

[S3-3] S3 guideline for non-restful sleep / sleep disorders of the German Society for Sleep Research and Sleep Medicine (DGSM). In: AWMF online (as of 2009)

[Morgenthaler-4] Timothy Morgenthaler et al., Standards of Practice Committee, American Academy of Sleep Medicine: Practice Parameters for the Use of Actigraphy in the Assessment of Sleep and Sleep Disorders: An Update for 2007 . In: Sleep . tape 30 , no. 4 , 2007, p. 519-529 , PMID 17520797 (English).