Actimetry

Actimetry is the measurement and analysis of locomotor activity in humans or animals using motion sensors. It typically uses wearable accelerometers mounted on the wrist or other body sites, or non-contact infrared sensors, to record movement continuously over days to weeks. Data are usually summarized in fixed time epochs (commonly 30 or 60 seconds) as activity counts and then analyzed to infer sleep-wake patterns, circadian rhythmicity, physical activity levels, and responses to interventions. In practice, actigraphy is the common clinical and research application of actimetry.

Devices include wrist-worn actigraphs and portable accelerometers, and data can be processed to yield metrics such as total activity, sleep onset and wake times, sleep efficiency, and wake after sleep onset. More advanced analyses extract rhythmic parameters such as interdaily stability, intradaily variability, and cosinor-derived measures (mesor, amplitude, acrophase).

Applications span sleep medicine (classification of insomnia, circadian rhythm disorders, circadian misalignment), psychiatry (assessment of mood disorders), neurology (gait and motor activity in Parkinson's disease), geriatrics and pediatrics (functional status and activity levels), and pharmacology (drug effects on activity). In animal research, actimetry records locomotor activity in home cages or open-field tests.

Limitations include dependence on device placement and wear-time, limited ability to classify movement type, potential artefacts from non-physiological movements, and variability across devices and algorithms. Interpretation typically requires validation against gold standards such as polysomnography for sleep research.

See also: Actigraphy, accelerometer, circadian rhythm.