Physical performance tasks: What are the underlying constructs?

Objectives: To investigate the structural validity of a battery of physical performance tasks and to investigate the construct validity of the resulting factors. Design: A measurement study. Setting: A large, private orthopedic clinic and a physical therapy clinic in an urban area. Participants: One hundred three consecutive adult patients with low back pain who were referred for physical therapy assessment. Interventions: Not applicable. Main Outcome Measures: The physical performance battery was composed of the 50-foot speed walk, 5-minute walk, repeated trunk flexion, sit to stand, loaded reach, rollover tasks, and Sorensen upper-body lift. Participants also completed 5 self-report measures. Results: Two correlated (.74) factors, speed and coordination and endurance and strength, were derived from the physical performance tasks. The Sorenson upper-body lift task was the only indicator that was not useful in defining the factors. Both factors had statistically significant correlations with measures of physical disability, lack of self-efficacy, and negative affect. Both factors had a trivial correlation with a numeric rating of pain intensity. Conclusions: There is support for 2 meaningful empiric groupings (ie, the derived factors) of the performance tasks. Pain intensity had a trivial overlap with speed-coordination and endurance-strength factors.