Before diving into guidelines, mortality data, or accelerometers, it helps to nail down what “physical activity” actually means — the terms below get used constantly across this site, and several of them are easy to confuse with each other.
What Is Physical Activity?
Physical activity (PA) is any bodily movement produced by skeletal muscles that results in energy expenditure above resting levels. It’s a broader category than “exercise” — exercise is just one type of physical activity.
- Physical activity — all movement that increases energy expenditure.
- Exercise — planned, structured, repetitive PA performed specifically to improve or maintain fitness.
- Incidental physical activity (IPA) — movement accumulated during everyday life that isn’t primarily done for exercise.
- Sedentary behavior — waking behavior performed while sitting, reclining, or lying down, with very low energy expenditure.
- MVPA — moderate-to-vigorous physical activity. LPA — light physical activity. VPA — vigorous physical activity.
A person can technically meet exercise recommendations — say, a 45-minute gym session — and still accumulate substantial sedentary time for the rest of the day. Meeting an exercise target and having a physically active lifestyle are not the same thing.
Physical Activity and Energy Expenditure
Total daily energy expenditure (TDEE) breaks down into three components:
TDEE = Resting energy expenditure + Thermic effect of food + Activity energy expenditure
Activity energy expenditure covers both deliberate exercise and everyday movement. The piece specific to movement is Physical Activity Energy Expenditure (PAEE) — energy expended through bodily movement above resting metabolism. It can be expressed in kcal/day, kJ/day, MET-minutes, or MET-hours (1 kcal ≈ 4.184 kJ, so kcal/day = kJ/day ÷ 4.184). PAEE is useful epidemiologically because it captures the energetic contribution of movement, rather than just whether someone “exercises” or not.
Incidental Physical Activity (IPA)
IPA is movement accumulated as part of normal daily living rather than planned exercise — walking between buildings, climbing stairs, household chores, running errands, occupational movement, standing and moving around, transportation-related walking, and brief bursts of faster movement. Because these small movements repeat throughout the day, IPA can add up to a substantial share of daily energy expenditure.
This distinction matters in practice: someone might complete a 45-minute gym workout and then sit for most of the rest of the day. Someone else might never formally “exercise” but accumulate substantial movement through transportation, work, stairs, and daily tasks. Traditional PA questionnaires tend to emphasize exercise and MVPA specifically, which means they can miss large amounts of this lower-intensity or intermittent movement entirely.
NEAT — Non-Exercise Activity Thermogenesis
NEAT is energy expenditure from activities that aren’t sleeping, eating, or purposeful exercise — standing, walking, fidgeting, occupational activity, household movement, and other spontaneous movement. James Levine’s research helped establish NEAT as a major, underappreciated source of variability in daily energy expenditure between individuals.
NEAT and IPA overlap heavily but describe slightly different things: IPA describes the behavior (the movement itself), while NEAT describes the energy expenditure that behavior produces. The two terms get used interchangeably fairly often, but technically they aren’t the same thing — one is the activity, the other is its metabolic cost.