The study, published in the Journal of Activity, Sedentary and Sleep Behaviors, was conducted by researchers at the Federal University of Ouro Preto in Brazil, led by Luciene Teixeira Paixão, Layana Amaral Neves and Luiz Antônio Alves de Menezes-Júnior. The team analyzed data from 5,533 American adults aged 18 to 65, a subset of the 9,254 people surveyed in the 2017–2018 NHANES cycle after excluding participants outside the age range or those missing information on body mass index, physical activity or sleep. The sample was 51.8 percent female, with roughly two-thirds of participants between 26 and 64 years old, and a differential loss analysis confirmed that the excluded participants did not differ significantly in age, gender, income or ethnicity from those included, reducing concerns about selection bias.

What sets this study apart methodologically is the way it handled the interplay between movement behaviors. Rather than treating sitting time and exercise as independent variables, the researchers calculated a ratio: minutes of moderate to vigorous physical activity, or MVPA, accumulated for every hour of sedentary behavior. This approach acknowledges a fundamental constraint of human physiology — the 24-hour day is fixed, so time spent in one behavior necessarily displaces time available for others, including sleep. The team applied thresholds drawn from the literature, notably the work of Chastin and colleagues in 2021, testing whether accumulating at least 1, 2.5 or 10 minutes of MVPA per sedentary hour was sufficient to offset the effects of a sedentary lifestyle on sleep duration.

Sedentary behavior was assessed through interviewer-administered questionnaires based on the Global Physical Activity Questionnaire developed by the World Health Organization, with participants reporting how much time they typically spend sitting each day. Physical activity was captured separately for two distinct domains: leisure and occupation. For leisure, participants described sports, fitness and recreational activities such as brisk walking, cycling, swimming or running, reporting how many days per week and how many minutes per day they engaged in moderate and vigorous efforts. For work, they described job-related activities such as carrying light loads or heavy lifting and construction tasks. Sleep duration was self-reported as the average hours slept per night, combining weekday and weekend estimates, and classified against the National Sleep Foundation’s recommendation of seven to nine hours for adults.

The descriptive picture that emerged was sobering. Participants averaged nearly nine hours of sitting per day, with occupational MVPA averaging about 88 minutes daily compared with just under 24 minutes of leisure-time MVPA. Nearly 60 percent of participants failed to reach sufficient activity levels per sedentary hour at work, and 62.5 percent fell short during leisure time. Sleep fared better: participants averaged roughly seven and a half to eight hours per night, and 84 to 87 percent achieved recommended or acceptable sleep duration, leaving about 13 percent with inadequate sleep. Statistical tests linked sleep duration to age, race and ethnicity, income and leisure-time physical activity, but not to gender, obesity or work-related physical activity in the simple bivariate comparisons.

The multivariate logistic regression results, adjusted for sex, age group, ethnicity, income, body mass index, caffeine intake, diagnosed medical conditions and use of medications for diabetes, hypertension, cardiovascular disease, sleep disorders, pain and mental health conditions, revealed the study’s central paradox. Adults who accumulated at least 2.5 minutes of leisure-time MVPA for every sedentary hour were 38.9 percent less likely to experience short sleep, with an odds ratio of 0.72. Even one minute of leisure activity per sedentary hour conferred a 40.8 percent reduction in the odds of short sleep. Yet among those who performed the same volume of activity at work, the pattern reversed: workers accumulating at least 2.5 minutes of occupational MVPA per sedentary hour were 57 percent more likely to sleep too little, and at the 10-minute threshold the odds of short sleep rose by 65 percent.

The authors attribute this divergence to what occupational health researchers call the physical activity paradox. Leisure-time exercise is typically voluntary, self-paced and performed in environments that promote relaxation and enjoyment. Physiologically, it helps regulate circadian rhythms, reduce muscle tension and lower cortisol levels, all of which facilitate the transition to restful sleep. It is also culturally framed as self-care, which may reinforce its psychological benefits. Occupational physical activity, by contrast, is compulsory, often repetitive, and frequently performed under time pressure, in hot or hazardous conditions, or with inadequate recovery between shifts. The sustained elevations in heart rate and persistent muscle tension associated with demanding labor can impair the body’s ability to wind down, and previous research has linked physically strenuous jobs to reduced sleep duration and quality, elevated blood pressure and even increased risk of myocardial infarction.

The stratified analyses added important nuance. The protective effect of leisure-time activity and the harmful effect of occupational activity held most clearly among adults aged 26 to 64 and among men, while women showed the leisure-time protective pattern prominently. No significant associations emerged for the youngest or oldest participants, possibly because irregular sleep schedules and screen exposure in young adults, and sleep fragmentation with reduced sleep efficiency in older adults, blunt the benefits of activity on sleep duration. Socioeconomic status produced the most striking differences: among low-income participants, leisure-time activity protected sleep while occupational activity showed no significant association; among middle-income participants, occupational activity was a risk factor; and among high-income participants, no significant associations appeared at all, perhaps because greater control over schedules and better living conditions buffer the negative effects of intense exertion.

The public health implications are considerable, particularly for socioeconomically disadvantaged workers. People in lower-income positions are more likely to hold physically demanding jobs that offer little flexibility or support for recovery, and they often lack access to resources that promote restful sleep, such as adequate free time, stress management programs or ergonomic adjustments. The authors suggest that workplace interventions — regular breaks, wellness programs, adjustable workstations allowing alternation between sitting and standing, stretching and meditation practices — could help mitigate the negative effects of occupational exertion on sleep. At the same time, promoting voluntary leisure-time activity remains a powerful, low-cost strategy for improving sleep health at the population level.

The study is not without limitations. All measures of activity, sitting and sleep were self-reported, which introduces memory and social desirability biases and can lead to underestimation or overestimation of true activity levels, in contrast to the objective accelerometry data used in some prior research. The thresholds applied were derived from accelerometer-based studies, and the simplified MVPA-to-sitting ratio cannot distinguish between different types of sedentary behavior, such as desk work versus social sitting, which may carry different health risks. The analysis also relied on a single NHANES cycle, limiting the ability to track changes over time, although the researchers note that the relevant sleep variables were only consistently collected from 2017 onward. Still, the core message stands out with unusual clarity: when it comes to sleep, the context of physical activity matters as much as the quantity. A workout you choose can help you sleep; a workload imposed on you may keep you awake.

Subject of Research: Associations between sedentary behavior, leisure-time and occupational physical activity, and sleep duration in US adults

Article Title: Influence of sedentary behavior and physical activity in leisure and work on sleep duration: data from NHANES 2017–2018

Article References: Paixão, L. T., Neves, L. A., & de Menezes-Júnior, L. A. A. (2024). Influence of sedentary behavior and physical activity in leisure and work on sleep duration: data from NHANES 2017–2018. Journal of Activity, Sedentary and Sleep Behaviors, 3(1), Article 26. https://doi.org/10.1186/s44167-024-00067-3

Image Credits: AI Generated

DOI: 10.1186/s44167-024-00067-3

Keywords: sleep duration, sedentary behavior, physical activity, NHANES, occupational health, leisure-time exercise, MVPA, sleep health, physical activity paradox, public health, cross-sectional study, socioeconomic status