SUMMARY
Objective: To demonstrate the feasibility and application of ‘continuous focal sampling’ direct observation (CFS DO) for physical activity (PA) measurement in free-living adults. Methods: Nine observers were trained to use CFS DO and completed two video-based examinations to evaluate observer reliability. We applied the method in free-living conditions by recording activity type and intensity among thirty college-aged students during 11.1 ± 1.0 hr observation periods. Results: Percent correct classification of activity type and intensity by the observers were 86.6 ± 6.5% and 76.1 ± 15.4%, respectively. Test-retest reliability coefficients for activity type and activity intensity were r = .79 and r = .78. Based on CFS DO measures, participants spent 57.4% and 15.5% of the time sitting and walking. Mean time spent in sedentary, light, moderate, and vigorous physical activity intensities were 359.6 ± 100.1, 178.8 ± 107.3, 85.4 ± 63.1, and 24.6 ± 24.6 min for the 11.1 ± 1.0 hr observation period. Conclusion: The CFS DO technique was reliable for assessment of free-living PA in the current study. Feasibility of CFS DO may be limited to shorter blocks of observation (2-3 hr).