Physical Performance Tasks: What Are the Underlying Constructs? Diane M. Novy, PhD, Maureen J. Simmonds, PT, PhD, C. Ellen Lee, PT, MS ABSTRACT. Novy DM, Simmonds MJ, Lee CE. Physical performance tasks: What are the underlying constructs? Arch Phys Med Rehabil 2002;83:44-7. 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 bat- tery 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 coordina- tion and endurance and strength, were derived from the phys- ical 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 mea- sures 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. Key Words: Low back pain; Physical endurance; Rehabil- itation. © 2002 by the American Congress of Rehabilitation Medi- cine and the American Academy of Physical Medicine and Rehabilitation L OW BACK PAIN (LBP) is a common, complex, costly, and controversial problem. Traditionally, standard clinical assessments of LBP have focused on the degree of impairment in the lower back (eg, range of motion, muscle strength as they relate specifically to the back). The present trend is to comple- ment impairment measures with functionally based measures that address more globally a person’s physical limitations. The present study addresses unresolved measurement issues on a battery of physical performance tasks that are examples of functionally based measures. The current status of physical performance tasks has evolved from studies of patients with LBP and normal controls. In the first studies, Simmonds et al 1-3 investigated various perfor- mance tasks to represent the domain of physical performance. Based on solid interrater agreement, test-rest reliabilities, and convergent and discriminant validity, they recommend using the 50-foot speed walk, 5-minute walk, repeated trunk flexion, sit to stand, loaded reach, and Sorensen upper-body lift tasks as indicators of overall physical performance. In a subsequent study, 4 these researchers reported preliminary data to suggest that 2 related constructs underlie the physical performance tasks. Specifically, they used a discriminant function analysis to investigate gender differences on the performance tasks. This analysis revealed constructs pertaining to endurance and strength and to velocity and coordination. The velocity-coor- dination construct was defined by 5-minute distance walk and loaded reach, whereas the endurance-strength construct was defined by 50-foot speed walk, trunk flexion, and sit to stand tasks. 4 The Sorensen upper-body lift task appeared to be a weak indicator of these constructs. However, confirmation or disconfirmation of the use of the upper-body lift task needs to be investigated further. In a recent effort to expand the performance task battery, Simmonds’s 1-3 team piloted another a rollover task on a sample of patients with LBP. A needed next step is to assess the use of the rollover task in conjunction with the rest of the established performance battery. The purpose of the present study was to identify the perfor- mance tasks that contribute to the overall structural validity of the performance battery, giving particular attention to the ques- tionable upper-body lift task and the previously unresearched rollover task. Related to this, it is important to investigate common factors that underlie the different performance tasks. To gain a clearer understanding of the constructs, it also is important to investigate patterns of correlation between the constructs and external variables such as depression, pain in- tensity, physical limitation, and self-efficacy related to the performance of certain functional tasks. METHODS Participants The participants were 103 consecutive adult patients with LBP referred for physical therapy assessment from a large, private orthopedic clinic and a physical therapy clinic in an urban area. The physical performance battery was incorporated as part of the routine physical therapy clinical intake examina- tion. The participants ranged in age from 19 to 82 years (average age  standard deviation [SD], 45  12.88yr). Sixty- one participants were women. Fifteen percent of the partici- pants had a previous back surgery. Other clinical characteris- From the Departments of Anesthesiology and Psychiatry and Behavioral Sciences, University of Texas-Houston Health Science Center, Houston, TX (Novy); and the Department of Physical Therapy, Texas Woman’s University, Houston, TX (Sim- monds, Lee). Accepted March 7, 2001. Supported in part by Texas Woman’s University Research Enhancement Award Grant (grant no. 10-0131382) and the National Institutes of Health Extramural Associates Research Development Award research pilot project (grant no. 1997-8). No commercial party having a direct financial interest in the results of the research supporting this article has or will confer a benefit upon the author(s) or upon any organization with which the author(s) is/are associated. Reprint requests to Diane M. Novy, PhD, Dept of Anesthesiology, University of Texas-Houston Medical School, 6431 Fannin, MSB 5.020, Houston, TX 77030, e-mail: diane.novy@uth.tmc.edu. 0003-9993/02/8301-6621$35.00/0 doi:10.1053/apmr.2002.27397 44 Arch Phys Med Rehabil Vol 83, January 2002