There is currently a great need to expend the knowledge base of various functional capacity measures used in the rehabilitation of chronic low back pain (CLBP) patients. In the current study, the functional performance of lifting capacity differences among four separate CLBP patient groups were examined by using standardized isokinetic and isoinertial lifting performance measurements. One hundred ninety-three consecutive patients were assessed at three separate points in time: at initial evaluation (PRE), at admission to the intensive 3-week phase of a functional restoration program (ADM), and after program discharge and follow up (FU) (an average of 12 weeks later), Group 1 (n = 26) consisted of postdiscectomy CLBP men; Group 2 (n = 91) consisted of nonsurgical CLBP men; Group 3 (n = 17) consisted of postdiscectomy women; and Group 4 (n = 59) consisted of nonsurgical women. Results comparing admission scores to postdischarge scores revealed that all four groups demonstrated a significant increase (P<0.01) in Liftask and progressive isoinertial lifting evaluation performance. Increases in performance were virtually identical for nonoperative and postoperative patients, with postdiscectomy men and women actually achieving peak isokinetic lifting forces higher than unoperated patients at the program's conclusion. This achievement in human performance was not found for the progressive isoinertial lifting evaluation test. Overall, these findings illustrate the utility of quantitative functional capacity measures, and provides objective evidence of the gains achieved by the patients. If theri isokinetic lifting is viewed as a functional paradigm for lumbar spine activities of daily lifting (as running relates to ADLs for knees and ankles), the post-treatment achievement of normal for near-normal) lifting capacity at maximum medical improvement is noteworthy. Considering that most patients demonstrate significant postrehabilitation residual impariment of lumbar mobility and strenght, the achievement of normal overall body function attests to the body's ability to maintain adequate performance levels by substitution and compensation for impaired spinal regions, much as it compensates for degeneration or instability in extremity joints. These results also clearly demonstrate the effectiveness of a functional restoration program to enhance gains in human performance in CLBP patients with and without prior surgery, As important, these results provide a sueful database for future comparison of Liftask and PILE performance by chronic CLBP patients before and after an effective rehabilitation program.