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Physical activity measures in the Millennium Cohort Study

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Learn about the Millennium Cohort Study (MCS) and its measurement of physical activity

Longitudinal study description

The Millennium Cohort Study (MCS) is the youngest of the current UK national longitudinal studies and involves just over 19,000 families with babies born around the millennium (Sep 2000- Jan 2002) in England, Wales, Scotland, and Northern Ireland [105]. The study was set up to be multidisciplinary, focusing on a range of experiences and outcomes of children and their families, including physical and mental health, whilst collecting rich social, economic, and demographic data on participants to understand how these shape outcomes. The first sweep was carried out when study children were around 9 months old and they have since been followed up at age 3, 5, 7, 11, 14y and recently at age 17y. In childhood, main carers (mainly mothers) have provided information through interviews, and if present their partners have also taken part. Teachers have provided data in some sweeps. Physical measurements and assessments of children’s skills and abilities have been carried out, and from age 11y study children have completed their own questionnaires. Fieldwork for the age 17y sweep was completed in 2019 with data released in the autumn of 2020.

The MCS was included in the COVID-19 waves of data collection in the British birth cohorts. A web-based interview was carried out in May 2020 (Wave 1), September-October 2020 (Wave 2), and February-March 2021 (Wave 3), when MCS members were aged ~20 years.

Physical activity overview (3 to 20y)

MCS contains childhood self-reported measures across physical activity domains (from 3-14y). Leisure time was measured at ages 3, 5, 7, 11, 14, and 17y (and 19-20y in the COVID-19 waves); active travel was measured at ages 5, 7, 11, 14, and 17y; and sedentary behaviour measured at age 3, 5, 7, 11, 14, and 17y (and 19-20y in the COVID-19 waves). Domestic activity was only measured in the COVID-19 waves at 19-20y.

With regard to comparability across time, overall engagement in leisure time activities is comparable in duration (weekly), while those indicating specific activity/sport are comparable in intensity. The COVID-19 waves are slightly different to the core waves as they measure leisure activity as daily duration and do not include the same level of information about the specific activities so are not directly comparable with the earlier waves. However, they are directly comparable to the other cohorts included in the COVID-19 waves. The form of active travel used is comparable across ages. Finally, measures of sedentary behaviour duration (hrs/day) while using TV, video games, and smartphones are comparable across ages.

At age 14y, participants also completed time-use diaries that included physical activity data from one weekday and one weekend day collected through paper forms, a mobile application, or online form. Data was recorded in 10-minute slots throughout the day from 4am.

Additionally, objective measures of physical activity (minutes of sedentary, light, and moderate to vigorous intensity physical activity) were captured at age 7y using the Actigraph GT1M accelerometer, waist-worn (Actigraph, Pensacola, Florida); and at age 14y using the GENEActiv accelerometer, wrist-worn (Activinsights, Kimbolton, England). Raw accelerometry data and derived variables are available for the age 7y data, and derived variables are available at age 14y.

Data access

MCS data are freely accessible to bona fide researchers by applying through the UK Data Service. More information on MCS is available on the CLS website. The raw accelerometer data from age 14y is available on request from the CLS Data Access Committee.

Learn about the other studies covered by this guide and their measurement of physical activity:

Explore the measures by physical activity domain and their cross-study comparability:

Further information:

This page is part of the CLOSER resource: ‘Physical activity across age and study: a guide to data in six CLOSER studies’.