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TABLE 1

Characteristics of inactivity physiology and nonexercise physical activity

Inactivity physiology
Inactivity physiology defined Acute and chronic physiological effects of sedentary behaviors (nonexercise activity deficiency) 
Modality An emphasis on sedentary behaviors while not standing (mostly sitting in humans) 
Reference comparison Nonexercise physical activity (NEAT-producing behaviors) 
Energetics Activity energy expenditure is low during most types of sitting compared with even light-intensity movements when standing 
Potential outcomes of prolonged sitting Cardiovascular disease (Fig. 2), mortality (Fig. 2), metabolic syndrome (refs. 21–24), obesity (refs. 4,5), and deep venous thrombosis (refs. 48–53) 
Cellular mechanisms Largely understudied, potentially distinct from exercise (example in Table 2; Figs. 5 and 6) 
Inactivity physiology
Inactivity physiology defined Acute and chronic physiological effects of sedentary behaviors (nonexercise activity deficiency) 
Modality An emphasis on sedentary behaviors while not standing (mostly sitting in humans) 
Reference comparison Nonexercise physical activity (NEAT-producing behaviors) 
Energetics Activity energy expenditure is low during most types of sitting compared with even light-intensity movements when standing 
Potential outcomes of prolonged sitting Cardiovascular disease (Fig. 2), mortality (Fig. 2), metabolic syndrome (refs. 21–24), obesity (refs. 4,5), and deep venous thrombosis (refs. 48–53) 
Cellular mechanisms Largely understudied, potentially distinct from exercise (example in Table 2; Figs. 5 and 6) 
Nonexercise physical activity
Frequency Up to dozens/hundreds of bouts of nonexercise activity per day; always 7 days/week 
Intensity Highly variable but often low (<3 METS or <25–50% Vo2max
Duration Prolonged, often >8 h/day; highly variable (Fig. 3) 
Modality Primarily involving movements while standing; leisure or non–leisure time physical activity 
Prescription Currently, 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 
Nonexercise physical activity
Frequency Up to dozens/hundreds of bouts of nonexercise activity per day; always 7 days/week 
Intensity Highly variable but often low (<3 METS or <25–50% Vo2max
Duration Prolonged, often >8 h/day; highly variable (Fig. 3) 
Modality Primarily involving movements while standing; leisure or non–leisure time physical activity 
Prescription Currently, 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.

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