actigraphs

Actigraphs are wearable motion sensors that record acceleration to infer activity levels over time. Most are worn on the wrist and produce a time series of activity counts per epoch, commonly 30 seconds, which reflect limb movement. Actigraphy is used to estimate sleep–wake patterns and circadian rhythms in both clinical and research settings, often during at-home monitoring.

Devices and data interpretation rely on accelerometry to generate metrics such as total activity counts, sleep onset latency, total sleep time, wake after sleep onset, and sleep efficiency. Data can be displayed as actograms showing daily activity rhythms and exported for analysis with specialized software. Sleep–wake classification typically employs validated algorithms, including Cole-Kripke and Sadeh, to assign each epoch as asleep or awake. In addition to sleep metrics, actigraphy supports studies of daily activity patterns, circadian phase, and fatigue-related risk.

Applications span clinical and population research. Actigraphy is used to assess sleep disorders, circadian rhythm disruptions, depression and other psychiatric conditions, pediatric and elderly sleep, obesity and metabolic health, and sleep in shift workers or hospitalized patients. It is valued for long-term, noninvasive, naturalistic monitoring outside laboratory settings, complementing polysomnography when full sleep staging is unnecessary or impractical.

Limitations include reliance on movement as a proxy for sleep, which can misclassify quiet wakefulness and short naps. Accuracy varies with epoch length, device placement, and wear compliance, and there is no universal standard for data processing. Devices from different manufacturers and varying algorithms can yield noncomparable results. Combining actigraphy with sleep diaries can improve interpretation and reduce misclassification.