Research Review By Dr. Jeff Muir©


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Date Posted:

March 2013

Study Title:

Is a positive clinical outcome after exercise therapy for chronic non-specific low back pain contingent upon a corresponding improvement in the targeted aspect(s) of performance? A systematic review


Steiger F, Wirth B, de Bruin ED, et al.

Author's Affiliations:

Institute of Human Movement Sciences and Sport, ETH Zurich; Spine Center Division, Department of Research and Development, Schulthess Klinik, Zurich, Switzerland

Publication Information:

European Spine Journal 2012; 21: 575-598.

Background Information:

Studies examining the effects of exercise therapy in the treatment of chronic non-specific low back pain (cLBP) show, in general, only moderate effectiveness (we know it is effective when looking at the literature as a whole, but the results are not highly consistent). This is often explained by the contradiction between the heterogeneity of cLBP patients and the uniformity of the exercise therapy approaches studied. Some suggest tailoring exercise programs to specific subgroups of patients, based on injury; however, there is little evidence that individually tailored or specific exercise programs show better success, which raises some doubt about this approach (3).

Current treatments for cLBP may be ineffective because they are based on the unsubstantiated assumption that the problem is located in the lower back itself, and is the result of a specific functional deficit that might be remedied by a specific type of exercise. Treatments utilized to target these dysfunctions can be expensive, requiring individual treatment, specially trained therapists, and/or specialized equipment. If there is no evidence that specific exercises are actually required, they may represent an unnecessary drain on already limited health-care resources.

The European guidelines for the management of cLBP briefly reported on the relationship between changes in physical performance and changes in clinical outcome, and found that the associations were tenuous, at best. Therefore, the aim of this study was to perform a systematic review of the studies that have examined this phenomenon.

Pertinent Results:

From an initial search returning 1217 articles, 18 articles (13 RCTs, 5 non-RCTs) were deemed appropriate and were included in the review.

Correlation between changes in pain and changes in sagittal mobility:
Nine studies reported that there was no correlation between changes in pain and changes in sagittal mobility, while one reported a low, but significant correlation. The total correlation was very low (r = -0.009). However, the I-squared factor was high (68.4%) indicating high heterogeneity.

Correlation between changes in pain and changes in rotational and lateral mobility:
One study found weak, significant negative correlations between changes in pain and rotational and lateral mobility (r = -0.35 and r = -0.35, respectively). A second study found a weak, significant correlation between pain and rotational total mobility (r = -0.22) and pain and total mobility in lateral flexion (r = -0.12).

Correlation between changes in pain and changes in extension strength:
Seven studies reported that there was no correlation between these attributes. Four of these studies reported the actual coefficients, two found no significant correlation (r = -0.4 and r = 0.2) and two reported a significant correlation (r = 0.56 and r = 0.55). The meta-analysis resulted in a total correlation of 0.262. Again, the I-squared factor was high (90.70%), indicating high heterogeneity.

Correlation between changes in pain with changes in flexion strength:
Four studies reported that there was no correlation. The one study that reported correlation coefficients showed a weak non-significant correlation (r = 0.01).

Correlation between changes in pain and changes in muscular endurance:
Seven studies examined the relationship between changes in pain and changes in muscular endurance, but none of them reported any specific correlation coefficients.

Correlation between changes in disability and changes in spinal mobility:
Three of the five studies reported that they found no correlation (one reporting r = -0.02, p = 0.86), one found a significant correlation, but only in women (beta coefficient in multiple regression = 0.29, p < 0.05), while the second study found a weak, but significant correlation (r = 0.18, p = 0.04).

Correlation between changes in disability and changes in muscular endurance:
No studies were found reporting the correlation between changes in disability and changes in muscular endurance.

Clinical Application & Conclusions:

The aim of this systematic review was to study the relationship between changes in clinical outcome (pain, disability) and changes in physical function (range of motion, strength, muscular endurance) as a result of physical therapy and exercise interventions aimed at treating cLBP. The majority of the 18 studies reviewed indicated that no such relationship exists. Changes in pain showed no significant correlation with changes in mobility, trunk extensor strength, trunk flexor strength or back muscle endurance. The authors conclude that there is not convincing evidence that changes in pain are strongly associated with changes in physical function or performance.

With respect to disability, a predominance of studies showed no significant correlation with changes in mobility or changes in trunk extensor strength. Regarding the value of exercise as it relates to chronic LBP, it is often not clear whether changes in performance are responsible for improvements in pain/disability, or whether these two simply occur coincidentally and are actually mediated by a common third factor. Recently, the popular intervention of core-strengthening exercises (focusing on strengthening the transversus abdominus, rectus abdominus, obliques, and erector spinae muscles) was questioned in a study that sought to compare this type of exercise with a general non-specific strengthening program (1). The outcomes were similar in the two treatment groups, and the authors concluded that focusing specifically on core exercises might be a potential mistake in the rehabilitation of cLBP. Furthermore, it was shown in another study (2) that even stretching exercises appeared to improve strength, which is difficult to explain on any physiological basis. The best mode of exercise to address cLBP, therefore, remains controversial and may be case/patient specific.

Based on their findings, the authors suggest that changes in physical function are largely unable to explain changes in the clinical condition in cLBP patients, and that the important ‘side effects’ of exercise therapy (including, amongst other things, changes in psychological variables such as fear-avoidance beliefs, catastrophizing and self-efficacy regarding pain control) should be more specifically emphasized and investigated in future rehabilitation programs.

Study Methods:

  • Databases searched: Medline and Pre-Medline with Ovid, Cochrane library with Wiley, and Embase.
  • Study selection: A study was considered eligible for inclusion in the review if it was a randomized controlled trial (RCT) or a non-randomized controlled trial (non-RCT) in English or German, examining the results of a physical activity intervention on patient reported outcome in cLBP. The studies had to investigate the effects of exercise and/or a physical therapy
  • Exclusion criteria: Studies that evaluated the effectiveness of drugs, transcutaneous electrical stimulation and other non-exercise therapy modalities were excluded from the review.
  • Outcomes of interest: those related to physical function/performance (strength, mobility, muscular endurance); as well as clinical outcomes (pain, disability).
  • Data extraction: One author independently extracted the following information from each study selected for inclusion:
    1. characteristics of the study participants;
    2. type of intervention (including type, duration, frequency of training);
    3. type of outcome measure (pain scores, disability scores, strength measurements, mobility scores, and muscular endurance measures); and
    4. statements concerning correlations and/or correlation coefficients for the relationship between clinical variables and performance outcomes.

Study Strengths / Weaknesses:

The authors acknowledged several limitations with their study, including:
  • The search strategy was limited to published studies identified through the selected search engines.
  • A publication bias may have been present, as well as a language bias, given that the authors restricted their search to English and German language publications. As there were only 12 randomized trials, the authors also included several observational studies, the results of which may be affected by confounding bias due to the absence of random assignment.
  • Most studies that did conduct correlation analyses, did not report any corresponding data (correlation coefficients) substantiating their reported non-significant correlations that would otherwise have allowed for quantitative data analysis with meta-analyses.
  • The interventions themselves were heterogeneous in their design and of variable quality.

Additional References:

  1. Kell RT, Asmundson GJG. A comparison of two forms of periodized exercise rehabilitation programs in the management of chronic nonspecific low-back pain. J Strength Cond Res 2009; 23(2): 513–523.
  2. Khalil TM, Asfour SS, Martinez LM et al. Stretching in the rehabilitation of low-back pain patients. Spine 1992; 17(3): 311–317.
  3. Wand BM, O’Connell NE. Chronic non-specific low back Pain - sub-groups or a single mechanism? BMC Musculoskelet Disord 2008; 9: 11.