title: Intensity and duration of physical efforts in Physical Education classes.
abstract: OBJECTIVE
  To evaluate the intensity and duration of physical efforts in Physical Education classes in primary and secondary school.
  
  
  METHODS
  School-based cross-sectional study carried out by means of the observation of 218 Physical Education classes, including a total of 272 students (each one of the students was evaluated three times). The study was carried out in the city of Pelotas (Southern Brazil), between August and December 2009. In order to evaluate the intensity of the efforts, accelerometers were used and the following cut-off points were adopted (in counts per minute): sedentary activities (0-100), light activities (101-2,000), moderate (2,001-4,999), vigorous (5,000-7,999), and very vigorous activities (>8000).
  
  
  RESULTS
  The mean duration of the classes was 35.6 minutes (SD 6.0). The mean proportion of time spent in moderate to vigorous physical activity was 32.7% (SD 25.2). Boys (44.1%) were involved significantly more in moderate to vigorous physical activity as compared to girls (21.0%; p<0.01). Students who practice physical activities outside the classes participated more in moderate to vigorous physical activity in the Physical Education classes.
  
  
  CONCLUSIONS
  Besides the fact that Physical Education classes have a short duration, students practice moderate to vigorous physical activity during one third of the class, with a poor significant contribution to students' level of physical activity.
authors.affiliation: Instituto Federal Sul-Rio-Grandense, Pelotas, Brasil.
authors.forename: Marina Marques
authors.initials: MM
authors.lastname: Kremer
authors.forename: Felipe Fossati
authors.initials: FF
authors.lastname: Reichert
authors.forename: Pedro Curi
authors.initials: PC
authors.lastname: Hallal
mesh_terms: D000293:Adolescent; D001938:Brazil; D002648:Child; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D008297:Male; D009043:Motor Activity / Q000502:physiology*; D010806:Physical Education and Training; D005082:Physical Exertion / Q000502:physiology*; D012574:Schools; D012737:Sex Factors; D013334:Students; D013997:Time Factors