RATIONALE: Exposure in vivo therapy aims to reduce pain-related fear - a key maintaining factor of chronic low back pain- while increasing level of daily functioning, despite the pain. This is done by exposing patients to their most feared activities/movements, while behavioral experiments are performed that serve to correct catastrophic (erroneous) beliefs about pain. Yet, performing exposure exercises might be very threatening for patients and might encourage them to build in subtle safety-seeking behavior. Whether safety-seeking behavior should be allowed or not during therapy is heavily debated. Whereas some argue that it will only interfere with therapeutic progress because it prevents the disconfirming experience exposure tries to offer, other argue that it will facilitate therapeutic progress because it enhances one's sense of control, if used judiciously. So far (clinical-)experimental studies have provided mixed evidence nor have they lead to any clinical recommendation. Hence, in a replicated single-case experiment, we will compare exposure therapy with versus exposure without safety-seeking behavior versus exposure only.

STUDY POPULATION: Participants are chronic low back pain patients seeking treatment, who fulfill all inclusion and exclusion criteria and participate voluntarily.

INTERVENTION: All participants receive exposure therapy at the rehabilitation department of the academic hospital in Maastricht, but with different recommendations for the use of safety-seeking behavior.

We will assess: 1) daily measures of fear, pain intensity and self-reported achievement of goals and 2) non-daily measures of pain disability, pain-related fear, pain catastrophizing, pain solutions, need to control and safety-seeking behavior. To measure to the influence of safety-seeking behavior on actual level of functioning, two behavioral performance tasks will also be presented, ie. a bag carrying task and a personalized task.

BURDEN AND RISKS: There are no risks associated with participation to this study that are not otherwise related to rehabilitation and movement in general and participation is completely voluntary. Participants are requested to fill out questionnaires on a daily basis at home (computerized if possible), as well as on different time points during the study and at follow up and perform two behavioral performance tasks. This study could help to further improve the beneficial long-term effects of exposure.

Inclusion Criteria:

• Suffer from chronic low back pain not caused by serious spinal injury, for at least 3 to 6 months
• Report a sufficient level of disability (this is in itself already a criterion to start treatment at the Rehabilitation department) and
• Moderate to high levels of pain-related fear (TSK > 37 or at least 4 items with a score of 3 or >3)
• Have a partner willing to participate

Exclusion Criteria:

• Specific medical disorder or cardiovascular disease preventing participation in physical exercise
• Serious psychopathologic co-morbidity. This is checked during anamnesis in the intake session with the rehabilitation physician and during the screening (standard care, see session 1 and session 2). When psychopathologic co-morbidity is detected, patients cannot participate in the study and may not be suitable candidates for exposure therapy entirely. Any decision regarding treatment recommendation is made with the entire treatment team. Furthermore, the researcher performing the therapy has a Master's degree in Clinical Psychology, which adds to the treatment team's expertise on psychopathology.
• Alcohol or drug abuse, i.e., at least one out of the four following criteria needs to be fulfilled: continued use despite social or interpersonal problems; repeated use resulting in failure to fulfill obligations at work, school, or home; repeated use resulting in physically hazardous situations; use resulting in legal problems (according to the Diagnostic Statistical Manual of Mental disorders, 4th ed.). This is assessed by the rehabilitation physician during the first session.
• Illiteracy
• Pregnancy
• Involvement in litigation concerning the patient's ability to work or disability income
• Non-Dutch speaking