title: Temporal trends in physical activity: a systematic review.
abstract: BACKGROUND
  In spite of all accumulated scientific knowledge on the benefits of physical activity (PA) for health, high rates of sedentary lifestyle are still observed worldwide. The aim of this study was to systematically review articles on temporal trends of PA and fitness, with emphasis on differences between children/ adolescents and adults.
  
  
  METHODS
  An electronic search at the Medline/PubMed database was carried out using the following combination of keywords: temporal trends or trends or surveillance or monitoring and PA or exercise or physical fitness or motor activity or sedentary or fitness.
  
  
  RESULTS
  By using this strategy, 23,088 manuscripts were detected. After examination, 41 articles fulfilled all inclusion criteria, and were, therefore, included. The data currently available in the literature for adults shows that leisure-time activity levels tend to be increasing over time, while occupational-related PA is decreasing over time. Youth PA seems to be decreasing over time, including a lower level of activity in physical education classes. As a consequence, fitness levels are also declining.
  
  
  CONCLUSIONS
  PA surveillance must be strongly encouraged in all settings and age groups. Special attention must be paid to low and middle-income countries, where PA surveillance is virtually inexistent.
authors: Post-Graduate Program in Epidemiology, Federal University of Pelotas, Brazil.
authors: Alan G
authors: AG
authors: Knuth
authors: Pedro C
authors: PC
authors: Hallal
mesh_terms: D000293:Adolescent; D000328:Adult; D000367:Age Factors; D000368:Aged; D002648:Child; D015444:Exercise; D006801:Humans; D007899:Leisure Activities; D008137:Longitudinal Studies; D008875:Middle Aged; D010809:Physical Fitness; D013997:Time Factors; D017132:Workplace; D055815:Young Adult