Variability of some objective measures of physical activity

Med Sci Sports Exerc. 1992 Oct;24(10):1167-72.


The purpose of this study was to determine how many days subjects should be monitored to provide an estimate of habitual physical activity in employed men engaged in a wide range of occupations. Caloric intake, movement recorders (accelerometers and pedometers), and heart rate were the measurements studied in 30 subjects who were monitored during their waking hours for 7 continuous days. A repeated measures ANOVA showed no significant difference between days (P > 0.05) for any of the measures when only weekdays were compared. However, when weekend days were included a majority of the measures showed a significant F-ratio (P < 0.05). An estimate was made of the number of days required to measure a 7-d period with less than 5% error. The average for all the different measures was 4.9 d. It appears that at least 5 or 6 d are needed to minimize the intra-individual variance a reasonable degree. Weekdays as well as weekend days need to be included.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Adult
  • Aged
  • Energy Intake
  • Energy Metabolism
  • Exercise*
  • Heart Rate
  • Humans
  • Male
  • Middle Aged
  • Monitoring, Physiologic*
  • Reproducibility of Results
  • Research Design*
  • Time Factors