This study is a secondary data analysis of the Hearts & Parks (H&P) crossover randomized controlled trial, a clinic-community collaboration targeted towards reducing childhood obesity among children in North Carolina (NC). Participants were enrolled between February 8, 2018 and March 10, 2020.[23] However, to ensure similar time duration for the statistical comparison between pre-closure and during-closure values, we only include data starting March 1, 2019 for this analysis. Prior to the pandemic, H&P enrolled and randomized 260 children and adolescents with obesity into either the 6-month clinic-community intervention or a waitlist control group, who received usual care until they entered the intervention at 6 months. In the intervention, patients received care at a pediatric weight management program and were able to participate in a structured play and exercise program, Bull City Fit, delivered at a local parks and recreation center. In Bull City Fit (offered 6 days/week), participants engaged in 60 minutes of PA at every session and were offered weekly nutrition education. The waitlist control group was a six-month waitlisted group, where participants received a non-obesity-related literacy intervention during the first six months, after which they were invited to participate in the intervention for the remaining six months. The study was approved by the Duke Health Institutional Review Board (IRB# Pro00086684) and was funded by the American Heart Association (AHA) Strategically Focused Research Network 17SFRN33670990.
The COVID-19 pandemic led to the closure of Bull City Fit in-person sessions as well as in-person school closures beginning on March 15, 2020. For the purposes of our analysis, we define "pre-closure” to be the period between March 1, 2019 and March 14, 2020, “during-closure” to be the period between March 15, 2020 and March 31, 2021, and “post-closure” to be the period between April 1, 2021 and June 30, 2021. These time frames were chosen based on the announcement of stay-at-home orders for North Carolina (announced on Saturday, March 14, 2020)[24], and when most schools in the Durham school district returned to in person learning (April 2021). The inclusion criteria for H&P required that they live in a geographic radius such that the majority of, if not all, children would be attending a public, private, or charter school in Durham County. Given that the number of participants who wore fitness trackers varied over time, sample sizes vary for the different periods.
Outcomes. The primary outcomes of interest were PA (defined as step count), bedtime, waketime, and sleep duration pre-, during-, and post- the COVID-19-associated closures.
Physical Activity. PA was measured objectively using step counts from a water-resistant Garmin VivoFit 3 wristband, chosen for its long battery life to last for the study duration without the need for charging. Participants were instructed to wear the watch 24 hours a day for the entire one-year study duration. The Garmin Connect app was downloaded and set up on participants’ or their parents’ smartphones. Parents and/or participants were instructed to sync the smartwatches to the app at least once a week. Garmin data were collected and aggregated by Pattern Health Technologies, Inc., who provide digital health platforms to manage health programs. Fifteen-minute epoch-level (where epoch is the time interval for which step count information was provided) step count information was transformed into daily step counts, which was then used to calculate average daily step counts per month (available for n = 252). Zero values were not reported by Pattern Health or Garmin, and thus it was not possible to differentiate non-wear time from sedentary times from the step count data alone. To address this, we leveraged mean motion intensity (MMI), a metric reported by the Garmin device, as a proxy for watch wear. MMI is a proprietary measure provided for each activity epoch that can take on values between 0 and 7, where 0 corresponds to no activity intensity and 7 corresponds to the greatest measurable activity intensity. We defined non-wear as MMI < 1 and used this definition to remove data corresponding to non-wear times from analysis, which resulted in data availability for 218 participants. From there, we only included in this analysis participants who had sufficient step count data covering the entire pre-, during-, and post-closure period between March 1, 2019 and June 30, 2021. Hence, for the subsequent analysis, we employed a data-driven approach and only included data for participants who had more than 60 days of valid data, where a valid day required more than 41% wear time (the presence of more than 40 out of the 96 possible epochs that can be reported in 24 hours) and only considered valid days for analysis. This resulted in data from 94 participants being included in the final PA analysis presented here (female: 55.3%, median age: 9.7 years) (Supplementary Figs. 1 and 2; Table 1), with n = 93 (female: 54.8%, median age: 9.7 years), n = 53 (female: 52.8%, median age: 9.8 years) and n = 8 (female: 50%, median age: 8.8 years) for pre-closure, during-closure, and post-closure, respectively. The post-closure sample size was fairly small in our analysis but we report average PA and sleep metrics post-closure to offer a potential trend in PA and sleep patterns directions.
Table 1
| Overall n (%) | Pre-closure n(%) | During-closure n(%) | Post-closure n(%) |
Age Groups (years) | | | | |
5–10 | 65 (69%) | 64 (69%) | 37 (70%) | 5 (63%) |
11–13 | 16 (17%) | 16 (17%) | 9 (17%) | 0 (0%) |
14–18 | 13 (14%) | 13 (14%) | 7 (13%) | 3 (37%) |
Gender | | | | |
Male | 42 (45%) | 42 (45%) | 25 (47%) | 4 (50%) |
Female | 52 (55%) | 51 (55%) | 28 (53%) | 4 (50%) |
Race | | | | |
Other | 37 (39%) | 37 (40%) | 21 (40%) | 0 (0%) |
Black/African American | 32 (34%) | 31 (33%) | 21 (40%) | 4 (50%) |
White | 21 (22%) | 21 (23%) | 9 (17%) | 2 (25%) |
Multiracial | 2 (2%) | 2 (2%) | 0 (0%) | 0 (0%) |
Native Hawaiian/Pacific Islander | 1 (1%) | 1 (1%) | 1 (2%) | 2 (25%) |
Missing | 1 (1%) | 1 (1%) | 1 (2%) | 0 (0%) |
Ethnicity | | | | |
Not Hispanic | 51 (54%) | 50 (54%) | 27 (51%) | 5 (63%) |
Hispanic | 43 (46%) | 43 (46%) | 26 (49%) | 3 (37%) |
Treatment Group | | | | |
Intervention | 50 (53%) | 49 (53%) | 26 (49%) | 5 (63%) |
Waitlist Control | 44 (47%) | 44 (47%) | 27 (51%) | 3 (37%) |
To account for activities that occurred during school hours, we also explored step counts only during the times when children were expected to be in school (7:00 AM – 4:00 PM on non-summer weekdays). Step count values were extracted on weekdays for all months excluding the summer months of June, July and August, when schools are typically on break.
Sleep. Sleep was measured objectively using the Garmin wristband. Sleep epochs were detected by Garmin’s proprietary sleep detection algorithm, and reported in seconds. Sleep epochs varied in duration as expected based on the number of sleep episodes detected and their individual durations.[25] Some nights had multiple sleep epochs for single participants, indicating disturbed sleep, movement during sleep, improper watch wear during sleep, or algorithmic error. The sleep periods labeled by Garmin were used for the sleep duration, bedtime, and waketime analysis.
DATA/STATISTICAL ANALYSIS
Step data were aggregated at the daily level for each participant by summing the step count within each epoch for each day only for epochs with an associated MMI ≥ 1. The average daily steps per month were calculated for each participant, and then averaged across all participants to calculate the average daily step count per month for the entire cohort. These average values and their standard deviations were reported for each of the three time periods: pre-closure, during-closure and post-closure (n = 93, 53, and 8, respectively), to enable comparison of PA during each period and to explore whether a relationship would emerge between PA and closures. For analysis of PA during school times, step count observations beginning from 7:00 AM and before 4:00 PM on weekdays, for all months except June, July and August, were included. Daily step count (averaged by month) for school times were calculated in the same way as the overall step count analysis described above (n = 93, 52 and 8, respectively for pre-closure, during-closure and post-closure).
For the sleep analysis, we used the time stamp of the earliest sleep epoch recorded after 6:00 PM on that day and 8:00 AM the following day to define the sleep start time, or bedtime. Similarly, we defined waketime as the latest sleep end time among all such epochs. If the bedtime was after midnight, the bedtime date was adjusted to be the date for the previous day. Total daily sleep duration per participant was calculated as the sum of the durations of all sleep epochs for each day. Average bedtime, waketime, and sleep duration per participant were calculated for each month, and these values were averaged for all participants to obtain the overall population average. Average bedtime, and waketime were each rounded to the nearest 15 minutes and were reported, along with the standard deviations, for each of the three time periods: pre-closure, during-closure and post-closure. Additionally, we report summer bedtime and waketime values separately to emphasize similarities in trends during typical summer pre-closure and both school-year and summer months during-closure.
We performed the Mann Whitney U Test to determine whether step count and sleep duration were significantly changed between the pre- and during-closure periods. To account for variations that are potentially attributable to seasonal changes, pre-closure step counts and sleep durations were compared with the corresponding months during-closure. Given that the post-closure data was only available for a small number of participants (N = 8) and for a limited number of months, we exclude the post-closure data from the statistical analysis and only report the average values for all PA and sleep metrics post-closure.
All analyses were conducted using Python version 3.7.4 through Jupyter notebooks (Jupyter notebook 6.0.1) in the Duke Protected Analytics Computing Environment (PACE) given the sensitive nature of the data. The visualizations were generated using the Seaborn library in Python version 3.7.4.