Physical activity measurements affected participants' behavior in a randomized controlled trial

E.M.F. van Sluijs, van M.N. Poppel, J.W. Twisk, W. van Mechelen, Mireille N M van Poppel

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BACKGROUND AND OBJECTIVE: Assessing levels and determinants of physical activity as outcome measurements might have an independent effect on participant's physical activity behavior. The objective is to study this effect in a randomized controlled trial (RCT) promoting regular physical activity in Dutch general practice.

METHODS: Using a Solomon four-group design, participants were randomized twice. After randomization to a control or intervention-condition at general practice level (N = 29), participants were randomized to a group participating in measurements at baseline, 2 and 6 months (3M-group, N = 361), or a group only participating in measurements at 6 months (1M-group, N = 356). Outcome measures assessed at 6 months included: level of physical activity (self-reported and objectively measured with accelerometry), meeting ACSM/CDC guideline for regular physical activity, stage of change, and determinants of physical activity.

RESULTS: Follow-up data on 635 participants (89%) was collected. Statistically significant measurement effects were found for meeting the ACSM/CDC guideline (self-reported), self-efficacy for resisting relapse, knowledge, and on awareness. Other outcome measures showed positive trends, except stages of change.

CONCLUSION: Measurements of physical activity affect participant's physical activity behavior, possibly triggered by a raised awareness about their own physical activity level. Implications for future research are discussed, as well as methodologic limitations of the study design.

Original languageEnglish
Pages (from-to)404-411
Number of pages8
JournalJournal of Clinical Epidemiology
Issue number4
Publication statusPublished - Apr 2006


  • Adult
  • Aged
  • Awareness
  • Epidemiologic Methods
  • Family Practice
  • Female
  • Health Behavior
  • Health Promotion/methods
  • Humans
  • Male
  • Middle Aged
  • Motor Activity
  • Research Design
  • Self Efficacy
  • Treatment Outcome

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