What Is Actigraphy
Actigraphy is a method of tracking sleep and wake patterns using a small accelerometer worn on the wrist, typically for 7 to 14 consecutive days. The device records movement data continuously, and specialized software distinguishes sleep from wakefulness based on the assumption that prolonged stillness indicates sleep. Unlike sleep studies, actigraphy happens at home without electrodes or overnight lab visits.
How It Works
The actigraphy device samples motion every 15 to 60 seconds. When movement drops below a set threshold and remains low for several minutes, the algorithm marks those periods as sleep. The device captures your actual sleep environment, circadian rhythm patterns, and daytime activity levels without the artificial setup of a laboratory.
Raw data is downloaded and analyzed using validated algorithms. Most commonly, clinicians use the Cole-Kripke algorithm or similar scoring methods to interpret the data. The output shows total sleep time, sleep onset latency, number of awakenings, and sleep efficiency. Over a two-week period, actigraphy reveals whether your sleep is consistent, fragmented, or delayed relative to your intended schedule.
Clinical Applications in Sleep Disorders
For insomnia, actigraphy confirms whether reported poor sleep aligns with actual sleep metrics. Patients often underestimate how much they sleep due to sleep state misperception, a core feature of insomnia. Actigraphy data guides cognitive behavioral therapy for insomnia (CBT-I) treatment by establishing a baseline and tracking progress. Sleep restriction therapy, a CBT-I component, relies on actigraphy-derived total sleep time to determine safe bed time windows.
In circadian rhythm disorders, actigraphy reveals the timing and phase of sleep relative to the 24-hour day. A 5 to 7-day actigraphy run often detects delayed sleep phase, where sleep onset occurs 2 to 3 hours later than the desired bedtime, or advanced sleep phase, where sleep ends 2 to 3 hours earlier. For suspected sleep apnea, actigraphy cannot diagnose the condition but can confirm fragmented sleep patterns that prompt referral to polysomnography.
When Actigraphy Is Ordered
- Differentiating insomnia from other sleep disorders by documenting actual sleep duration and timing
- Monitoring sleep schedule consistency and sleep hygiene interventions over time
- Evaluating circadian rhythm alignment before light therapy or melatonin treatment
- Tracking treatment response in patients starting CPAP therapy or behavioral interventions
- Detecting irregular sleep patterns that suggest advanced or delayed sleep phase disorder
Key Limitations
Actigraphy cannot distinguish sleep stages (light, deep, REM) or detect apneas, hypopneas, or oxygen drops. Motion-based algorithms may misclassify quiet wakefulness as sleep and miss subtle restlessness. If your doctor suspects sleep apnea based on symptoms like gasping, pauses in breathing, or severe daytime sleepiness, polysomnography remains the gold standard test. Actigraphy also assumes consistent wear and accurate self-reporting of sleep and wake times, which affects accuracy.
Common Questions
- How accurate is actigraphy compared to actual sleep? Sensitivity ranges from 84% to 98% depending on the algorithm, but overestimation of sleep is common in people with insomnia. Using actigraphy alongside a sleep diary provides a more complete picture of perceived versus objective sleep.
- Can I shower or swim while wearing the actigraphy device? Most modern actigraphy watches are water-resistant up to 30 meters, safe for daily washing. Always confirm water resistance specifications with your sleep provider.
- How does actigraphy data inform sleep hygiene changes? If actigraphy shows fragmented sleep despite adequate time in bed, poor sleep hygiene factors like inconsistent bedtime, caffeine after 2 PM, or irregular wake time become treatment targets. The data motivates behavior change by showing patterns rather than relying on memory alone.
Related Concepts
- Sleep Diary - Subjective record you complete daily to track bedtime, wake time, and perceived sleep quality, often paired with actigraphy for validation
- Sleep Study - Polysomnographic test that measures brain waves, heart rate, breathing, and oxygen levels, more comprehensive than actigraphy but performed in a lab
- Sleep Efficiency - Percentage of time spent asleep relative to total time in bed, a key metric derived from actigraphy data