Physical activity, sedentary behaviour, sleep and light exposure

The Actigraph wGT3X-BT (Actigraph LLC, Pensacola, Florida, USA) is used to objectively monitor 24-hour physical activity, sedentary behaviour, sleep and light exposure.^{15 16} The wGT3X-BT is a triaxial accelerometer designed to record continuous high-resolution physical activity and sleep/wake information. It includes an integrated ambient light sensor that delivers lux values alongside activity information. Lux is a measure of light intensity. At visit 1, participants wear the device on their non-dominant wrist for 10 consecutive days. The device does not have to be removed during aquatic activities or showering. An information sheet describing how to wear the device correctly is provided. The actigraphy data will be downloaded using the ActiLife software and processed using the R package GGIR.¹⁷ Variables such as energy expenditure (MET-min/day), sleep/ wake parameters (total sleep time, total wake time and number of awakenings) and amount of light exposure (Lux) will be derived from the actigraphy data.

Questionnaires on physical activity, sedentary behaviour, sleep and light exposure are also administered at the same visit. Participants are interviewed using the modified International Physical Activity Questionnaire-Short Form (IPAQ-SF) to self-report their physical activity in the last 7 days.¹⁸ The modified questionnaire evaluates the vigorous physical activity, the moderate physical activity and the walking time. We removed question asking about the sitting time from the original IPAQ-SF and included it in the questionnaire used to assess sedentary behaviour. The data will be computed in metabolic equivalents (MET-min/week) scores. Questionnaire on sedentary behaviour which is modified from the Adult Sedentary Behaviour Questionnaire is performed.¹⁹ The questionnaire evaluates time spent sedentary in the last 7 days, including sitting time at work, sitting/lying down time to watch television, to use electronic devices at mealtimes, while driving or reading. Participants also self-administer the Pittsburgh Sleep Quality Index questionnaire to assess their sleep habits in the last month,²⁰ and the Harvard Light Exposure Assessment questionnaire to assess their main light sources exposure in hourly basis on a typical weekday and weekend day.²¹