Despite the acknowledgment that physical activity is important for health, there are still few population-based or school-based studies that uses the current physical activity guidelines for adolescents.

Physical inactivity was defined a less than 300 min/w of moderate to vigorous-intensity physical activity practice.

Previous research has shown very high prevalence rates of physically inactive adolescents and a strong association with demographic, socioeconomic and biological factors.

Based on this information, the investigators are elaborating a systematic review of literature to obtain and provide more accurate information in this context.

The objectives of this study were to (i) review extant literature on the prevalence of physical inactivity (PI) in adolescents of both sex (10-18 years old); (ii) compare its prevalence between developed and developing countries.

The search was carried out using online databases (Biomed Central, CINAHL, EMBASE, ERIC, MEDLINE, PsycInfo, Scopus, SPORTDiscus), references cited by retrieved articles and by contact with the authors, considering articles published from the establishment of the databanks until April 29th, 2010.

Inclusion Criteria:

• Cross-sectional studies.
• Original studies showed that physical inactivity is evaluated through a questionnaire.
• Studies which ranked 300> inactivity min/wk.

Exclusion Criteria:

• Studies did not assess physical inactivity through a questionnaire.
• Studies in which the participants were only overweight/obese, diabetics or suffering from another disease.

Samples of adolescents (age range 10-18y) without diseases and/or physical limitations.