Utility of actiwatch sleep monitor to assess waking movement behavior in older women.

PURPOSE: Wrist-worn accelerometer devices measure sleep in free-living settings. Few studies, however, have investigated whether these devices can also measure waking movement behavior (e.g., total movement volume, physical activity). The purpose of this study was to investigate the ability of a wrist-worn Actiwatch 2 sleep monitor to rank total movement volume and physical activity levels compared with a waist-worn ActiGraph GT1M accelerometer and self-reported leisure time physical activity, respectively. In addition, we compared temporally matched activity measured via the ActiGraph GT1M and Actiwatch 2 over the study week. METHODS: A subset of women from the Healthy Women Study (n = 145; age, 73.3 ± 1.7 yr) wore an Actiwatch 2 on their nondominant wrist and an ActiGraph GT1M on their dominant hip for seven consecutive days. Participants recorded their leisure time physical activity in a 7-d diary and completed the past year version of the Modifiable Activity Questionnaire. Analyses were conducted for all wake periods and separately for active periods when both devices were worn. RESULTS: Spearman rank-order correlation coefficients for total movement volume between the Actiwatch 2 and ActiGraph GT1M were significant for wake periods (r = 0.47, P < 0.001) and, to a lesser extent, for active periods (r = 0.26, P < 0.01). However, the Actiwatch 2 did not rank participant's physical activity levels similarly to self-reported leisure time physical activity estimates (κ ≤ 0.05, P > 0.05). Multilevel model analyses comparing temporally matched activity measured via the ActiGraph GT1M and Actiwatch 2 suggest that the two devices yielded similar levels of activity during wake periods (B = 0.90; SE, 0.008; P < 0.001) and during active periods (B = 0.81; SE, 0.01; P < 0.001). CONCLUSIONS: A wrist-worn Actiwatch 2 may be useful for ranking total movement volume and for assessing the pattern of activity over a day in older women. However, our data do not support using a wrist-worn Actiwatch 2 device for measuring physical activity.

Temporal relationships between physical activity and sleep in older women.

PURPOSE: The objective of this study is to examine the temporal and bidirectional relationships between accelerometer-derived physical activity estimates and actigraphy-assessed sleep characteristics among older women. METHODS: A subgroup of participants (N = 143, mean age = 73 yr) enrolled in the Healthy Women Study wore an ActiGraph accelerometer on their waist and an Actiwatch sleep monitor on their wrist concurrently for seven consecutive days. Multilevel models examined whether ActiGraph-assessed daily activity counts (ct·min⁻¹·d⁻¹) and moderate- to vigorous-intensity physical activity (MVPA; min·d⁻¹) predicted Actiwatch-assessed sleep onset latency, total sleep time, sleep efficiency, and sleep fragmentation. Similar models were used to determine whether nighttime sleep characteristics predicted physical activity the following day. RESULTS: In unadjusted models, greater daily activity counts (B = -0.05, P = 0.005) and more minutes of MVPA (B = -0.03, P = 0.01) were temporally associated with less total sleep time across the week. Greater sleep efficiency was associated with greater daily activity counts (B = 0.37, P = 0.01) and more minutes of MVPA (B = 0.64, P = 0.009) the following day. Less sleep fragmentation was also associated with greater daily activity counts and more MVPA the following day. Findings were similar after adjustment for age, education, body mass index, depressive symptoms, arthritis, and accelerometer wear time. CONCLUSIONS: Few studies have used objective measures to examine the temporal relationships between physical activity and sleep. Notably, these findings suggest that nightly variations in sleep efficiency influence physical activity the following day. Thus, improving overall sleep quality in addition to reducing nightly fluctuations in sleep may be important for encouraging a physically active lifestyle in older women.