The scientific motivation behind the study stems from a fundamental shift in how researchers think about physical activity, sedentary behaviour, and sleep. For decades, epidemiologists examined each of these behaviours in isolation, asking, for example, whether more exercise lowers the risk of heart disease or whether prolonged sitting raises the risk of type 2 diabetes. The evidence from such studies is clear: higher physical activity, less sedentary time, and adequate sleep are each associated with lower risks of cardiovascular disease, type 2 diabetes, obesity, several cancers, anxiety, depression, and premature mortality. But there is a hidden flaw in treating these behaviours separately. Time is finite. Every additional minute spent sitting is a minute not spent standing, stepping, or sleeping. The three behaviours are co-dependent components of a single twenty-four-hour whole, and analysing them independently distorts their true relationships with health.

This realisation has driven what researchers call the 24-hour movement paradigm, a framework that treats physical activity, sedentary behaviour, and sleep as inseparable parts of a daily time-use composition. The paradigm has already reshaped public health policy: several countries, including Canada, Australia, Thailand, South Africa, Saudi Arabia, and Egypt, along with the World Health Organization, have issued integrated 24-hour movement guidelines. Yet the first generation of these guidelines was built largely on studies that examined single behaviours in isolation, because rigorous evidence on their combined effects simply did not exist. The authors of the Canadian 24-hour movement guidelines for adults explicitly called for research with stronger designs, including longitudinal follow-up, device-measured behaviours, and attention to dimensions such as domain-specific activity, sleep consistency, napping, and daytime alertness. The Slovenian team designed the GIB study to answer exactly these calls.

The recruitment strategy leverages an existing national infrastructure. Every four years, the Statistical Office of Slovenia draws a nationally representative sample of 17,500 residents aged 18 to 74 from the Central Population Register, using stratified simple random sampling with region and settlement type as strata. These individuals are invited by post to complete the National Health-related Lifestyle Survey, conducted by the National Institute of Public Health, which historically achieves a response rate of around 60 percent. From the roughly 10,500 survey responders, the GIB team expects about 5 percent to accept an additional invitation to the device-based study, yielding approximately 525 participants per recruitment wave. The first baseline data collection took place in 2024, with subsequent waves planned for 2028, 2032, and beyond, creating a rolling cohort intended to span more than a decade.

At the heart of the measurement strategy sits the activPAL4micro, a small tri-axial accelerometer measuring just 4 by 2 by 0.4 centimetres and weighing 9 grams, which is attached to the front of the thigh. Unlike wrist-worn devices, thigh placement allows the monitor to distinguish posture with high precision: sitting, standing, lying, and stepping can be classified directly from body position rather than inferred from wrist movement. Participants wear the device for seven consecutive days, twenty-four hours per day, including during sleep, and simultaneously keep a diary recording bedtimes, wake times, naps, night-time awakenings, and, for employed participants, working hours. Sleep onset and offset are then determined by combining the algorithmic output with diary entries, with adjustments applied when the device records upright activity near the reported sleep window. The result is a complete, posture-based map of each participant’s entire week.

From these raw data, the researchers will construct two complementary time-use compositions. The first is posture-based, comprising stepping, standing, sitting, lying while awake, and sleeping. The second is movement-based, comprising moderate-to-vigorous physical activity, light-intensity physical activity, sedentary behaviour, and sleep. For employed participants, a third, domain-specific composition will separate occupational from non-occupational behaviour, allowing the team to ask whether physical activity at work carries the same health value as leisure-time exercise, a question with major implications for millions of workers in physically demanding jobs. Non-wear time will be proportionally reallocated to wake-time behaviours, daytime naps will be added to sleep time, and validated algorithms will process the event files in the R programming environment.

The device data will be complemented by an extensive battery of questionnaires. A novel ten-item instrument, the GIB24-Q, developed specifically for Slovenian population surveillance, asks about domain-specific moderate-to-vigorous activity, muscle-strengthening and balance exercise, walking, sedentary behaviour, recreational screen time, and sleep. The widely validated Global Physical Activity Questionnaire provides an international benchmark. The 46-item Healthy Built Environment Questionnaire captures perceptions of neighbourhood, home, and workplace environments, along with time spent outdoors and in nature. Each participant’s home address will also be linked to the Walk Score index, an open-access measure of neighbourhood walkability ranging from 0 to 100, and to environmental indicators including air quality and the number of days with high temperatures, enabling the team to test whether the places people live shape the way they move.

Well-being and health will be assessed through eight short validated instruments: the WHO-5 Well-being Index for subjective mental well-being, the Need for Recovery Scale for work-related fatigue, the International Fitness Scale for perceived fitness, the Epworth Sleepiness Scale for daytime sleepiness, the Fatigue Assessment Scale for chronic fatigue symptoms, the Satisfaction With Life Scale, the Perceived Time Poverty Scale, which measures the feeling of lacking freely disposable time, and the Nordic Musculoskeletal Questionnaire for pain across nine body regions. In parallel, each participant’s data will be linked to the National Health-related Lifestyle Survey, which covers demographics, diet, smoking, alcohol, self-rated health, diagnosed conditions, medication use, stress, social support, body mass index, and waist circumference. From 2028 onward, with additional informed consent, the team will link records to national registers covering healthcare utilisation, hospitalisations, drug prescriptions, sickness absence, retirement, disease incidence, and causes of death, all under strict data protection law and GDPR compliance.

The statistical approach is as innovative as the data collection. Because the components of a 24-hour composition are co-dependent, conventional regression is inappropriate; the team will instead apply compositional data analysis, expressing time-use as sets of isometric log-ratio coordinates before entering regression models, handling zeros with a log-ratio expectation-maximisation algorithm, and applying survey weights to preserve national representativeness. An a priori power analysis determined that the expected sample of roughly 472 participants per wave providing valid accelerometer data is sufficient to detect a minimum effect size of 0.2 with 80 percent power. For significant findings, the researchers will map what they call the Goldilocks Zone: the range of 24-hour movement compositions, estimated at ten-minute granularity, associated with the best 5 percent of predicted health outcomes, and will search for compositions that fall in the optimal zone across multiple health outcomes simultaneously.

The potential payoff is considerable. The GIB study will deliver the first device-measured estimates of 24-hour movement behaviours in a national sample of Slovenian adults, identify the socio-demographic and environmental factors that shape healthy and unhealthy time use, and clarify the relative importance of occupational versus leisure activity, sleep regularity, and specific postures for long-term health. As Slovenia develops its own 24-hour movement guidelines, the findings will provide directly relevant, population-specific evidence, and the team anticipates contributing data to international consortia pooling thigh-worn accelerometer records worldwide. If the study succeeds in defining Goldilocks Zones for daily time use, the humble question of how a nation spends its twenty-four hours could yield some of the most actionable health guidance of the coming decade.

Subject of Research: A longitudinal population-based study of 24-hour movement behaviours, their correlates, and health associations in Slovenian adults

Article Title: Prevalence, correlates, and health associations of 24-hour movement behaviours in Slovenian adults: a protocol for a longitudinal population-based study

Article References: Kastelic, K., Knific, T., & Šarabon, N. (2025). Prevalence, correlates, and health associations of 24-hour movement behaviours in Slovenian adults: a protocol for a longitudinal population-based study. Journal of Activity, Sedentary and Sleep Behaviors, 4(1), Article 3. https://doi.org/10.1186/s44167-025-00073-z

Image Credits: AI Generated

DOI: 10.1186/s44167-025-00073-z

Keywords: 24-hour movement behaviours, physical activity, sedentary behaviour, sleep, compositional data analysis, accelerometry, longitudinal study, population health, built environment, well-being, Slovenia, movement guidelines