The relationship between objectively and subjectively measured activity levels in people with chronic low back pain

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.

A cross-sectional study was performed in patients and controls.

The study was carried out in the daily environment of the 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.

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.

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.

Patient self-reports about their activity level are relatively inaccurate when compared to objective measurements.