Data: UK Household Longitudinal Study
We used data from UK Household Longitudinal Study (UKHLS) [21,22,23,24]. UKHLS is a nationally representative, longitudinal study of people in the UK that started in 2009 and comprises approximately 40,000 households. UKHLS contains a rich set of information relating to many aspects of respondents’ lives. The main survey is conducted annually with a two-year rolling window making up one wave.
From April 2020, selected participants were asked to complete monthly (every two months from September 2020) web-based surveys examining the impact of the COVID-19 pandemic on the welfare of UK individuals, families, and wider communities.
This paper utilises study waves that contain data on the participants’ physical activity. These include waves 7 (Jan 2015-Jun 2017), 9 (Jan 2017-Jun 2019), and 11 (Jan 2019-December 2021) from the annual UKHLS main survey and waves 1 (April 2020), 5 (September 2020), and 7 (January 2021) from the COVID-19 study. We dropped all observations from the annual wave 11 data that were collected after February 2020 to avoid capturing any effects of COVID-19.
Measures
Physical activity
Participants were asked to provide information on the number of days they were physically active for at least ten minutes at a time in the last seven days for three different types of physical activity: walking, moderate physical activity, and vigorous physical activity. Walking included that done “at work and at home, walking to travel from place to place, and any other walking that you might do solely for recreation, sport, exercise, or leisure”; moderate activities include those that “make you breathe somewhat harder than normal and may include carrying light loads, bicycling at a regular pace, or doubles tennis”; and vigorous activities include those that “make you breathe much harder than normal and may include heavy lifting, digging, aerobics or fast bicycling.”
Respondents who indicated they were physically active for ten minutes or more on at least one day were also asked how much time they spent being physically active (for each activity type) in a combination of hours and minutes on one of those days. Full details of survey methods are published by UKHLS [25].
We defined two binary variables to proxy whether individuals realised the physical activity levels recommended by the CMOs (henceforth referred to as being ‘physically active’). The first of which was the primary focus of our analysis and entailed coding individuals as 1 (Yes) if an individual completed at least 150 min of moderate physical activity or at least 75 min of vigorous physical activity per week. However, unlike UKHLS, the CMOs’ definition of moderate physical activity includes “brisk walking.” Hence, we also derived an alternative proxy variable where individuals were coded as 1 (Yes) if they completed at least 150 min of walking or moderate physical activity, or at least 75 min of vigorous physical activity. Individuals with missing data for total minutes of vigorous or moderate activity (or walking for alternative proxy variable) were not included in the analysis.
We derived an estimate of participants’ total minutes of physical activity per week for each type of activity by multiplying the reported total minutes of each activity by the number of days reportedly active. Full details of the questions and response options used to determine the participants’ physical activity in UKHLS annual and COVID-19 questionnaires are provided in ‘Additional File 2’.
We were able to determine whether 15,568 individuals (14,523 for alternative proxy variable) were physically active in at least one of the annual waves of data and at least one of the waves in the COVID-19 study. Of these, 3,660 (3,312 for alternative proxy variable) reported being aged 65 or over before March 2020. This subset of individuals was used as the core sample. Sociodemographic descriptive statistics of this sample are reported in ‘Additional File 3’.
Additional variables
UKHLS contains data relating to individual characteristics that could feasibly influence how lockdown affects trends in physical activity, and thus lead to widening pre-existing health inequalities. To examine differences in physical activity trends, we used data on respondent age and whether they had a self-reported long-standing physical or mental impairment, illness, or disability in at least one of the pre-COVID-19 annual waves of data. We also examined differences by stratifying the sample into tertiles based on individuals’ average level of physical activity across the pre-COVID-19 waves of data.
To examine differences in physical activity trends by neighbourhood deprivation, we used Office of National Statistics data containing information on respondents’ index of multiple deprivation (IMD; a scale from most deprived to least deprived) deciles for England (2019), Wales (2019), Scotland (2020) and Northern Ireland (2017). We used Lower Layer Super Output Area (LSOA) codes, or national equivalents, to link these to the UKHLS data.
We defined a ‘least deprived’ population and a ‘most deprived’ population. An individual was defined as belonging to the most deprived population if, for the respective nations (England, Scotland, Wales, Northern Ireland), the LSOA or equivalent they reside in has IMD ranking (from April 2020) below the median.
There were differing levels of missing data across the questions used to derive these additional variables. Therefore, where we stratified the sample, the sample size varies slightly across different analyses. ‘Additional File 4’ illustrates how the samples of respondents were determined.
Analysis
Empirical approach
We examined trends in the proportion of older individuals who were physically active both before and after the government-imposed lockdown in March 2020.
Stratifying by respondent characteristics
To examine how the trends varied by individual characteristics, and how lockdowns could have widened existing inequalities, we re-examined the trends after stratifying the sample by whether respondents (i) had a health condition, (ii) respondent age, (iii) the level of deprivation. Where the sample was stratified by age, we also examined trends for a comparator group of individuals who were aged 16–64 before March 2020.
Any change in the proportion of individuals who were physically active after the COVID-19 lockdown is an aggregation of those who were already physically active before lockdown and those that were more sedentary. The effect of lockdown is not necessarily homogenous for these groups and taking a simple average could mask these important differences. Hence, to further investigate differences among certain populations, we re-examined the trends after stratifying the sample into tertiles based on respondents’ total minutes of moderate activity and vigorous activity per week (i.e., the measures used to dichotomise the variable on whether physically active), averaged across pre-COVID-19 waves.
Seasonality
The season can affect activity levels, generally with lower levels of activity in the winter months and higher in summer [26]. This is largely driven by the climate and day length where, for example, the UK’s colder temperatures, greater levels of rainfall, and fewer sunshine hours in the winter months [27] are associated with less physical activity among older adults [28].
Given that before the introduction of the lockdown, data were collected over the year and after lockdown data were collected for specific months, changes in activity levels could be reflecting seasonality rather than the effect of an imposed lockdown. Hence, we re-examined the trends described, restricting the sample to respondents from whom data were collected one month on either side of April, September, and January.