TABLE 1

Characteristics of inactivity physiology and nonexercise physical activity

Inactivity physiology
Inactivity physiology definedAcute and chronic physiological effects of sedentary behaviors (nonexercise activity deficiency)
ModalityAn emphasis on sedentary behaviors while not standing (mostly sitting in humans)
Reference comparisonNonexercise physical activity (NEAT-producing behaviors)
EnergeticsActivity energy expenditure is low during most types of sitting compared with even light-intensity movements when standing
Potential outcomes of prolonged sittingCardiovascular disease (Fig. 2), mortality (Fig. 2), metabolic syndrome (refs. 2124), obesity (refs. 4,5), and deep venous thrombosis (refs. 4853)
Cellular mechanismsLargely understudied, potentially distinct from exercise (example in Table 2; Figs. 5 and 6)
Nonexercise physical activity
FrequencyUp to dozens/hundreds of bouts of nonexercise activity per day; always 7 days/week
IntensityHighly variable but often low (<3 METS or <25–50% Vo2max)
DurationProlonged, often >8 h/day; highly variable (Fig. 3)
ModalityPrimarily involving movements while standing; leisure or non–leisure time physical activity
PrescriptionCurrently, more vague than the exercise prescription; “limit sitting time” is the most direct; the specific interactions between frequency, intensity, duration, and modality of nonexercise activity to replace sedentary time are largely unknown
  • The defining characteristics of inactivity physiology and the unique patterns of nonexercise physical activity are listed. This can be contrasted to exercise physiology guidelines.