BACKGROUND: Functional capacity evaluation (FCE) requires determination of effort by observation of effort indexes for performance interpretation. Waddell signs have been shown to be associated with decreased functional performance. Whether determination of effort by observational criteria and Waddell sign testing can be used interchangeably to interpret lifting performance is unknown.
OBJECTIVE: The purposes of this study were to assess the concurrent validity of submaximal effort and Waddell signs and to determine whether these contribute independently to lifting performance.
DESIGN: This investigation was an analytical cross-sectional study.
METHODS: A total of 130 people who had chronic nonspecific low back pain and were referred for fitness-for-work evaluation were included. Physical effort was determined on the basis of observational criteria for lifting from floor to waist, lifting from waist to shoulder, and horizontal lifting during FCE. A second assessor conducted Waddell sign testing. The concurrent validity of Waddell signs and submaximal effort was assessed by calculating sensitivity and specificity. Hierarchical regression analysis was used to determine the contributions of Waddell signs and submaximal effort to lifting performance. Age and sex were covariates.
RESULTS: The FCE assessor found a low sensitivity of Waddell signs for submaximal effort determination. Between 53% and 63% of the participants who were classified as showing submaximal effort had Waddell signs. Waddell signs and submaximal effort were independent contributors to lifting performance. The contribution of submaximal effort was larger than that of Waddell signs, as shown by 20% to 29% higher explained variance in lifting performance when submaximal effort was added to the model first versus 3% to 6% higher explained variance when Waddell signs were added first.
LIMITATIONS: Assessor variability could have influenced the study results.
CONCLUSIONS: In people with chronic nonspecific low back pain, Waddell sign testing and determination of physical effort by observational criteria should not be used interchangeably to interpret lifting performance during FCE.