Validity of activity-based devices to estimate sleep

For some time, the importance of assessing physical activity as a critical health behavior has been recognized: reliable measurements of physical activity are useful in evaluating the role of physical activity in health promotion and also for evaluation of the relative effectiveness of public health programs and interventions.1 Large-scale epidemiological studies have incorporated both subjective and objective tools for assessing physical activity. The measurement of energy expenditure by doubly labeled water is the “gold standard,” though it is both costly and has limited extendibility.2 Accelerometry is one of the most commonly used methods for assessing free-living physical activity.3 Compared to other objective measures, it has been shown to be highly sensitive in detecting varying levels of physical activity,4,5 and is currently being used by the US National Health and Nutrition Examination Survey (NHANES IV).6 Sleep has also been recognized to be a key health attribute associated with energy expenditure and other health outcomes. Large-scale epidemiological studies have employed both objective and subjective tools for measurement of sleep-wake behavior. The “gold standard” measure of sleep is made using polysomnography (PSG), though wrist actigraphy has gained popularity over the past several decades as an important lower-cost and minimally invasive measurement alternative.7,8 Compared to PSG, actigraphy has been shown to be a reliable and valid instrument to assess sleep.9–11 The need to integrate measurement of both sleep and physical activity in population studies is clear, though no uniform approach exists to measure sleep and physical activity concurrently. Use of the same instrumentation for measuring both sleep and activity could accelerate the collection of more comprehensive physiological data while minimizing cost and participant burden. The same apparatus would likewise facilitate clinical monitoring of sleep and activity in clinical disorders of energy balance. Devices used for the estimation of sleep using wrist actigraphy and for the estimation of physical activity by core accelerometry are, however, very similar. Both are used to record a digitally integrated measurement of gross motor activity. The marketable difference between the 2 devices is as follows: whereas the core accelerometer is typically worn on the trunk and used to predict energy expenditure and activity data, the wrist actigraph is worn on an extremity; and the smaller movements of the wrist as compared to the trunk are used to infer time spent asleep and wake. BRIEF SUMMARY Current Knowledge/Study Rationale: Physical activity and sleep both are attributes important for health. Although objective, concurrent measurement of each could improve our understanding of risk of obesity and other health conditions, there are little data that address the validity of measuring these attributes using the same devices. Study Impact: This study supports the ability to use the same activity monitors to measure both physical activity and sleep, identifying the potential for future epidemiological and public health initiatives to measure both of these important health attributes concurrently. We aimed to test the hypothesis that a device specifically marketed for core accelerometry could be moved to the wrist and could generate data that would result in accurate estimation of sleep-wake states. We collected concurrent data from several actigraphy/ accelerometry devices in order to compare estimation of sleep. A sample of 30 participants in a Cleveland-based epidemiological research study using actigraphy to estimate sleep participated by wearing 3 devices on a single night concurrent with PSG.