Direct observation is a valid criterion for estimating physical activity and sedentary behavior

Area of Science:

• Exercise Physiology
• Human Movement Science
• Biomedical Engineering

Background:

• Validating physical activity and sedentary behavior measurement tools in free-living settings is crucial.
• Direct observation (DO) is a potential criterion measure, but its accuracy for absolute intensity assessment is unproven.
• Trained observers' ability to judge free-living activity intensity requires empirical evidence.

Purpose of the Study:

• To compare direct observation (DO) estimates of MET-hours and time in activity intensity categories with indirect calorimetry (IC).
• To establish the criterion validity of DO for assessing absolute physical activity intensity in free-living conditions.

Main Methods:

• Fifteen participants were directly observed for two hours daily over three days.
• Participants wore an Oxycon Mobile indirect calorimeter (IC) while engaging in self-selected activities.
• Activities ranged from sedentary tasks at a desk to using exercise equipment.

Main Results:

• DO accurately estimated total MET-hours with a -12.7% bias (ICC=0.98).
• DO precisely estimated time in low-intensity activity (2.1% bias, ICC=1.00) and moderate-to-vigorous intensity activity (-4.9% bias, ICC=1.00).

Conclusions:

• Direct observation (DO) is a valid criterion measure for assessing absolute physical activity intensity in free-living validation studies.
• DO provides accurate and precise estimates of energy expenditure (MET-hours) and time spent in different activity intensities.