Systematic Review: Strategies for Using Exercise Therapy To Improve Outcomes in Chronic Low Back Pain

Context Which types of exercise therapy are most beneficial to patients with nonspecific chronic low back pain? Contribution This Bayesian meta-regression of 43 trials suggests that the most effective exercises for improving pain and function in adults with chronic low back pain are stretching and strengthening, respectively. Exercise performed over longer periods of time seemed more effective than exercise performed less than 20 hours total. Supervised programs that were individually tailored seemed to be more effective than other delivery modes. Cautions Trials used various measures to assess pain and function, and many were small and of low quality. The Editors Exercise therapy is widely used as a treatment for low back pain. In our accompanying paper in this issue (1), we present the results of a systematic review, conducted within the framework of the Cochrane Collaboration. We assessed the effectiveness of exercise therapy for reducing pain and disability in adult nonspecific acute, subacute, and chronic low back pain compared with no treatment and other conservative treatments. We concluded that exercise therapy seems to be effective at slightly decreasing pain and improving function in adults with chronic low back pain, particularly in health care populations. In subacute low back pain, evidence suggests that a graded-activity program improves absenteeism outcomes, although evidence for other types of exercise is unclear. In acute low back pain, exercise therapy is as effective as either no treatment or other conservative treatments. Exercise therapy encompasses a heterogeneous group of interventions that vary in type, intensity, frequency, and duration of exercise and the setting in which it is provided. There continues to be uncertainty about the most effective approach (2), and the literature on the hypothesized mechanism of the effect of exercise interventions provides little guidance (3). Better understanding of important characteristics of the intervention would allow us to more fully inform clinical practice and future research in the application of exercise therapy. However, standard methods of meta-analysis are not ideal because they necessitate the exclusion of correlated data from trials investigating several treatment groups within studies and cannot include information from trials without comparison groups. We aimed to identify particular exercise intervention characteristics that decrease pain and improve function in adults with nonspecific chronic low back pain. Methods Review Methods Our search strategy included a computerized search of the electronic databases MEDLINE and EMBASE (up to October 2004), PsychInfo and CINAHL (1999 to October 2004), and the Cochrane Central Register of Controlled Trials (Issue 3, 2004). We searched citations and screened cited references of exercise reviews and contacted content experts for additional trials. We did not restrict the searches or inclusion criteria to any specific languages. We followed a standard protocol for study selection and data abstraction (4). Two reviewers independently assessed study eligibility, data extraction, trial quality, and clinical relevance. We used consensus and a third reviewer, if needed, to resolve disagreements. We extracted the data onto pretested standardized forms. Further details on the strategies for the search and identification of studies have been reported elsewhere (1). We included randomized, controlled trials if they investigated exercise therapy as an intervention for nonspecific low back pain, regardless of the comparison group or groups. Outcomes of interest were pain, function, return to work or absenteeism, and global improvement. We present analysis and results of the subgroup of 43 trials (3907 participants) that were conducted in the populations with chronic low back pain (lasting longer than 12 weeks) and adequately report the outcomes of pain and function. We measured pain and function as continuous variables, and we placed each study's results on a common 0- to 100-point scale to facilitate comparison and interpretability of the syntheses. On the basis of current literature on minimal clinically important differences, we considered a 20-point (out of 100 points) improvement in pain (5) and a 10-point (out of 100 points) improvement in functioning outcomes (6) to be clinically important. We used data from the available follow-up period closest to 6 weeks after randomization for all analyses. Exercise Intervention Characteristics We identified important intervention characteristics a priori, with the assistance of clinical experts. We characterized exercise interventions by the exercise program design, delivery type, dose or intensity, inclusion of additional interventions, and the types of exercises included. When necessary, we contacted authors for additional information. We categorized design of the exercise therapy program as individually designed, in which the treating therapist completed a clinical history and physical examination and delivered an exercise program specifically designed for the individual participant; partially individually designed, in which the exercise program included the same type of exercises but varied in intensity, duration, or both; or standard design, in which a fixed exercise program was delivered to all participants. We characterized delivery type of the exercise therapy as follows: 1) home exercises only, in which the participants met initially with therapists, then participated in the exercise program with no supervision or follow-up; 2) supervised home exercises, in which the participants met initially with therapists, participated in the exercise program, and had follow-up with their therapist at least every 6 weeks; 3) group supervision, in which participants attended exercise therapy sessions with 2 or more participants; and 4) individual supervision, in which participants received one-on-one intervention or supervision. We classified exercise therapy programs that included more than 1 type of delivery according to their main delivery type. We assessed dose or intensity of the exercise therapy by considering the duration and number of treatment sessions. If the exercise program included a home exercise component and study adherence information was not available, we used a best estimate of intervention dosage. We computed the best estimate for supervised home exercise programs (those with provider follow-up at least every 6 weeks) by using an adherence rate of 75% of the recommended time and number of sessions. For home exercise programs without follow-up, we used an adherence rate of 50% of the recommended time and number of sessions. We selected these rates from the observed adherence rate for home exercises, according to daily diary recordings (7) and therapist (7, 8) and patient (8-10) reporting of adherence to the prescribed programs. We dichotomized the dose of each exercise intervention to facilitate interpretation of resultshigh-dose exercises were those with 20 or more hours of intervention time, and low-dose exercises were those with less than 20 hours of intervention time. Twenty hours was the mean dose of the exercise interventions and seemed to distinguish exercise groups with respect to intensity. Sensitivity analyses using 15- and 25-hour cutoff points resulted in less than a 10% change in the grouping of studies. We considered additional treatment other than exercise therapy in the study groups to be a factor associated with effectiveness. We documented the use of and the specific type or types of additional treatments. Because several different additional treatments were used and there is uncertainty about effectiveness, we did not assess the effect of different additional treatment types. We recorded the types of exercises included in the exercise intervention groups. Muscle-strengthening exercises were interventions that primarily involved muscle contraction, were usually repeated many times, and were limited to specific muscle groups that aimed to increase muscle cross-sectional area and strength (11). Stretching exercises aimed to increase the amount of movement of a specific joint or series of joints and lengthen the presumably contracted or shortened muscles (11). Coordination exercises included training and used specific movements to improve the coordination or proprioception of movements and muscle function (12, 13). Mobilizing or flexibility exercises were repeated exercises, using controlled movements throughout a joint's normal range of motion. We noted specific extension mobilization and flexion mobilization exercises; these included controlled movements in these specific directions only. Aerobic exercises or general physical fitness included whole-body interventions that were added to normal activities of daily living and prescribed in a specified dose, for example, specific programs of walking, swimming, or cycling. We also identified other specific exercise therapies: McKenzie exercise therapy (14), functional restoration or the David Beck Clinic program (15, 16), Cesar therapy (17), and Mensendieck therapy (18). Because only a few studies were available, we could not assess these specific exercise therapies separately. Statistical Analysis We used meta-analysis and meta-regression analyses to synthesize the randomized, controlled trial data on the effect of exercise treatment and to assess the effect of exercise intervention characteristics. The outcomes in all analyses were the group-specific mean follow-up outcome measures. This allowed us to use data from several groups within a study and to assess the importance of predictors at the group or study levels (19). As usual in meta-analysis, we treated the reported within-group variances as true variances and appropriately divided them by group sample sizes to calculate variances of the means. We initially investigated the exercise treatment effect in a random-effects analysis