Dr. Macedo and others involved in the proposed research recently conducted a study that investigated whether simple clinical characteristics could identify patients who benefit more from either motor control exercises or graded activity. Results were statistically significant and clinically relevant demonstrating that a simple questionnaire could help aid the selection of the most appropriate exercise therapy for each individual patient. Therefore, we aim to conduct a randomized controlled trial following a similar approach to the original study to validate in a different sample the results of the effect modification analysis.

Dr. Macedo and others involved in the proposed research recently conducted a study that investigated whether simple clinical characteristics could identify patients who benefit more from either motor control exercises or graded activity. Motor control exercises (sometimes called lumbar stabilization exercises) and graded activity using the principles of cognitive behavioral therapy are two popular forms of exercise therapy with evidence of effectiveness from high quality systematic reviews, but no evidence for superiority of one approach over the other when tested in heterogenous populations. The results of a previously published study demonstrated that a simple 15-item questionnaire (Lumbar Spine Instability (LSI) Questionnaire) could identify patients who responded best to either motor control exercise or graded activity (interaction 2.72 95% CI 1.39 to 4.06, p=0.001). The results demonstrated that for people who are LSI negative, graded activity provided a much better outcome than motor control exercise one year post-intervention (a statistically and clinically significant improvement of 1.96 points on a 0-10 numeric function scale; p< 0.001). In people who were LSI positive, motor control exercise provided slightly better outcomes, compared to those prescribed motor control exercises. It is important to note that this study was measuring differences between treatments groups, and thus change in the scores of function presented represent differences between groups.

However, although this clinical decision rule has the potential to transform exercise treatment for LBP, especially given the relatively large interaction effects found, validation in an independent sample is essential before recommending use in clinical practice.There are three recognized steps in developing clinical decisions rules: derivation, validation and impact evaluation. Dr. Macedo's previous study falls within the first step of this process and the proposed study aims to address the second step; validation.

Therefore, the objective of this study is to conduct a randomized controlled trial following a similar approach to the original study to validate in a different sample the results of the effect modification analysis to identify baseline characteristics that predict/modify response to treatment.

Inclusion Criteria:

• Patients will be eligible for inclusion if they meet all of the following inclusion criteria: chronic non-specific LBP (>3 months) with or without leg pain, currently seeking care for LBP, between 18 to 80 years of age, English speaking (to allow response to the questionnaires and communication with the treating physiotherapist), Clinical assessment indicating that the participant is suitable for active exercises (by a family physician or using the Physical Activity Readiness Questionnaire), Moderate or greater pain or disability measured using question 7 or question 8 of the SF-36 Health Survey, moderate or High Risk Classification on the STarT Back Tool indicating appropriateness of physiotherapy and thus an exercise program.

Exclusion Criteria:

• Exclusion criteria will be known or suspected serious pathology, comorbidity that would prevent participation in exercise programs and scheduled for surgery during trial period.

Given that this is an exercise study blinding of participants and those delivering the exercise program will not be possible. Outcome measures will be collected by an investigator not aware of treatment allocation, but most outcome measures will be self-reported and thus, true assessor blinding will no be possible. All statistical analysis will be conducted by a blinded investigator.