OBJECTIVE: To compare self-report measures of daily activities with objective 
activity data to determine whether patients with chronic lower back pain report 
their activity levels as accurately as controls do.
DESIGN: A cross-sectional study was performed in patients and controls.
SETTING: The study was carried out in the daily environment of the subjects.
SUBJECTS: Thirty-two chronic lower back pain patients with symptoms more than 
three months and 20 healthy controls from the Netherlands, aged 18-65 years.
MAIN MEASURES: A tri-axial accelerometer was worn for five weekdays and the 
Baecke Physical Activity Questionnaire was filled in. Pearson's correlation was 
calculated to get insight in the awareness of patients and controls. Comparisons 
of the relationship between the objective and subjective scores of each 
individual patient with those of the group of controls were used to allocate 
each patient into subgroups: overestimators, underestimators and aware patients. 
Physical and psychological characteristics of these groups were explored.
RESULTS: Patients showed weak correlations between the objective and subjective 
scores of physical activity and appear to have problems in estimating their 
activity levels (r = -0.27), in contrast to controls who showed strong 
correlations between the objective and subjective scores (r = 0.66). Comparison 
of the individual relationships of patients with those of controls showed that 
44% of the patients were not aware of their activity level. There were 
relatively more underestimators (30%) than overestimators (14%). Physical 
characteristics between the three groups tended to be different.
CONCLUSIONS: Patient self-reports about their activity level are relatively 
inaccurate when compared to objective measurements.