TABLE 1.
Key concepts—definitions and caveats.
| Concept | Definition | Caveats |
|---|---|---|
| 24-hour activity cycle (24-HAC) | Activities conducted over a 24-hour period including, sleep, sedentary behavior, light-intensity physical activity, and moderate-to-vigorous intensity physical activity.1 | These behaviors are interrelated and must be considered together when examining the impact of behavioral interventions or public policy. |
| Exercise | A subset of physical activity, that is, planned, structured, and repetitive.1 | N/A |
| Light intensity physical activity (LPA) | Physical activities requiring energy expenditures of 1.5 to < 3 METs. | N/A |
| Metabolic equivalent (MET) | Unit used to describe the absolute intensity of physical activity. A ratio of your working metabolic rate relative to your resting metabolic rate.1 | N/A |
| Moderate-to-vigorous intensity physical activity (MVPA) | Physical activities requiring energy expenditures of ≥ 3 METs. | N/A |
| Physical activity | Any bodily movement produced by skeletal muscles that requires energy expenditure.1 | This includes both exercise and non-exercise activity thermogenesis. Physical activity is typically described across domains such as transportation, occupational, leisure-time, etc. |
| Physical inactivity | An insufficient level of moderate-to-vigorous intensity physical activity level to meet present physical activity recommendations.1 | An individual who is physically inactive is often wrongly labelled as “sedentary”. |
| Sedentary behavior (SB) | Any waking behavior characterized by an energy expenditure < 1.5 METs, while in a seated, reclined, or supine posture.1 | The typical definition does not include quiet standing or standing-related behaviors with low energy expenditure, nor does it include squatting or kneeling behaviors such as those commonly seen in hunter-gatherer communities. |
| Sleep | Sleep is a recurring, reversible neuro-behavioral state of relative perceptual disengagement from and unresponsiveness to the environment. Sleep is typically accompanied (in humans) by postural recumbence, behavioral quiescence, and closed eyes.2 | Sleep time does not include time in bed while awake. Sleep also includes many different characteristics, with simple assessments of duration being an oversimplification of its impact on health, as well as the impact of other activity behaviors on sleep. |
| Standing | A stationary, upright posture, supported on one or two legs. | Considered separate from SB, though energy expenditure likely does not classify as LPA. |
Several definitions were previously published in 1Stoner L, Barone Gibbs B, Meyer ML, Fryer S, Credeur D, Paterson C, et al. A Primer on Repeated Sitting Exposure and the Cardiovascular System: Considerations for Study Design, Analysis, Interpretation, and Translation. Frontiers in Cardiovascular Medicine. 2021; 8 and 2Carskadon MA, Dement WC. Normal human sleep: an overview. In: Kryger MH, Roth T, Dement WC, editors. Principles and practice of sleep medicine. 4th ed. Philadelphia, PA: elsevier saunders; 2005. pp. 13–23.
24-HAC, 24-hour activity cycle; SB, sedentary behavior; PA, physical activity; LPA, light intensity physical activity; MVPA, moderate-to-vigorous intensity physical activity; MET, metabolic equivalent.