Here is the design of a clinical trial:

Official Title: The Effect of Graded Activity and Pain Education (GAPE) for Patients Early After Lumbar Spinal Fusion

Included conditions:
- Low Back Pain

Study Armgroups:
- {'label': 'Control group', 'type': 'NO_INTERVENTION', 'description': 'Usual care:\n\nBefore surgery all patients are invited to participate in a pre-surgery seminar, where they receive information and advice about the time before, during and after the LSF. The seminar will be guided by nurses, surgeons, anesthesiologist, occupational therapists and physiotherapist.\n\nAfter the surgery the patient will be hospitalized on an average of 3-4 days. During hospitalization a physiotherapist consults the patients on a daily basis to provide information, guidance on mobilization and instructions in gradually progressing movement. The patients will have no restrictions on movement after surgery and should gradually return to normal activity level.\n\nThree months post-operatively all patients will receive physical rehabilitation delivered by physiotherapists in a community care center.'}
- {'label': 'Intervention group: Graded Activity and Pain Education (GAPE)', 'type': 'EXPERIMENTAL', 'description': "Patients in the intervention-group will receive usual care and 9 sessions of GAPE, 4 sessions at the hospital, 2 sessions in the patient's home and 3 sessions by telephone.\n\nPain education in GAPE is viewed as an approach which target cognitive attitudes and beliefs about pain. The pain education will target 3 overall questions: 1. What is pain and is my pain normal? 2. What can affect my pain? 3. What can I do to relieve my pain? The education will be individually adjusted to each patient, so the patient's context and concerns regarding pain and movement are included.\n\nThe aim of Graded activity is to improve the patient's functional ability by positive reinforcement of health behaviors and activity levels. Graded activity will be based on which short-term activity-goals the patient evaluates as the most important for the treatment outcome. In close collaboration with the patient the physiotherapist will set quotas for the selected exercises/activities.", 'interventionNames': ['Behavioral: Graded Activity and Pain Education (GAPE)']}

Interventions:
- {'type': 'BEHAVIORAL', 'name': 'Graded Activity and Pain Education (GAPE)', 'description': "GAPE is based on a cognitive behavioral perspective that human behavior is affected by behavioral, cognitive and affective factors, this include the patient's perception of and response to pain. The perspective is a psycho-social perspective which amplify and interact with the individual patient's pathology.\n\nThe overall theoretical perspective in GAPE is that fear of movement and/or lack of self-efficacy for exercise can potentially lead to disuse and sedentary behavior, a perspective modified from the fear-avoidance model. In this modified version the patients´ and the physiotherapists´ former experiences, knowledge, and beliefs are factors influencing on the patients´ experience of pain and thereby their self-efficacy for exercise and fear of movement.", 'armGroupLabels': ['Intervention group: Graded Activity and Pain Education (GAPE)']}

Primary Outcomes:
- {'measure': 'Change from baseline in sedentary behavior (sitting or reclining/lying posture)', 'description': 'Sedentary behavior will in this study be defined as: "Any waking behavior characterized by a sitting or reclining/lying posture". Sedentary behavior will be assessed objectively as the number of minutes per day the patient is sedentary (lying down and sitting) measured by SENS motion activity measurement system. SENS is a small accelerometer placed within a small plaster to be worn on the patient\'s thigh. The SENS motion system is considered a reliable and valid device for measuring sedentary behavior. The patients will wear the accelerometer for 7 consecutive days during the week before surgery, and in 7 days at three- and 12-months post-surgery.', 'timeFrame': '3 months post-surgery'}

Please estimate the sample size based on the assumption: 
The power calculation is based on achieving at least 80% power, with an assumption of a 20% dropout rate.
Sample size
          The power calculation is based on the primary outcome, sedentary behaviour. A mean difference of 60âmin per day is considered a clinically significant difference, with a standard deviation of 115 [63]. A sample size of 59 per group is required to obtain a power of at least 80% to detect the mean difference of 60âmin. To account for a 20% drop-out, we will include 144 patients in total.