The convergent validity of free-living physical activity monitoring as an outcome measure of functional ability in people with chronic low back pain

The objective measurement of free-living physical activity may be a useful method of assessing functional ability in different patient groups. The aim of this study was to investigate the convergent validity of free-living physical activity, as an outcome measure of functional ability in people with chronic low back pain (CLBP). Thirty-eight participants with CLBP were recruited from five physiotherapy out-patient departments. All participants completed the Roland Morris Disability Questionnaire (RMDQ), a measure of self-reported functional ability, and performed three physical performance tests; repeated sit-to-stand test, 50-foot walk test and 5-minute walk test. Each participant then wore a physical activity monitor, continuously, over a one week period to measure free-living physical activity. A relatively weak but statistically significant relationship was found between all three measurement methods (r = 0.32 to 0.44, p < 0.05). The strength of the correlations suggests that each method measures a related but unique aspect of functional ability for this patient group. These results show that free-living physical activity monitoring possesses a level of convergent validity as an outcome measure of functional ability and may be a useful adjunct to current functional ability assessment techniques in individuals with CLBP.