Here is the design of a clinical trial:

Official Title: Repetitive Transcranial Magnetic Stimulation Alone and in Combination with Motor Control Exercise for the Treatment of Patients with Chronic Non-specific Low Back Pain (ExTraStim Trial): Study Protocol for a Randomized Controlled Trial

Included conditions:
- Chronic Low-back Pain

Study Armgroups:
- {'label': 'Active rTMS + Motor control exercises', 'type': 'EXPERIMENTAL', 'description': 'Active (real) repetitive transcranial magnetic stimulation (20 minutes), immediately followed by a session of motor control exercises taught and supervised by a physiotherapist (30 minutes).', 'interventionNames': ['Device: Active rTMS', 'Other: Motor Control Exercises']}
- {'label': 'Sham rTMS + Motor control exercises', 'type': 'SHAM_COMPARATOR', 'description': 'Sham repetitive transcranial magnetic stimulation (20 minutes), immediately followed by a session of motor control exercises taught and supervised by a physiotherapist (30 minutes).', 'interventionNames': ['Device: Sham rTMS', 'Other: Motor Control Exercises']}
- {'label': 'Active rTMS', 'type': 'EXPERIMENTAL', 'description': 'Active (real) repetitive transcranial magnetic stimulation (20 minutes).', 'interventionNames': ['Device: Active rTMS']}
- {'label': 'Sham rTMS', 'type': 'SHAM_COMPARATOR', 'description': 'Sham repetitive transcranial magnetic stimulation (20 minutes).', 'interventionNames': ['Device: Sham rTMS']}

Interventions:
- {'type': 'DEVICE', 'name': 'Active rTMS', 'description': 'A figure-of-8 coil connected to a biphasic Magstim Rapid 2 stimulator (The MagstimCo, Whitland, UK) will be used. Coil orientation and position will be guided throughout the experiment by a neuronavigation system (Brainsight, Rogue research, Montreal, QC, Canada). The intensity of rTMS will be set at 95 % of the first dorsal interosseous (FDI) resting motor threshold (RMT).\n\nActive rTMS will consist of 40 trains of 5 seconds each at 10 Hz (25-s intertrain interval) applied over M1 (on FDI cortical representation), for a total of 2000 stimulations lasting 20 minutes.', 'armGroupLabels': ['Active rTMS', 'Active rTMS + Motor control exercises'], 'otherNames': ['Repetitive Transcranial Magnetic Stimulation']}
- {'type': 'DEVICE', 'name': 'Sham rTMS', 'description': 'A sham coil will be use (e.g. equipped with a magnetic shield that blocks the magnetic field). The sham stimulation will last the same duration as the active rTMS (30 min).', 'armGroupLabels': ['Sham rTMS', 'Sham rTMS + Motor control exercises'], 'otherNames': ['Sham Repetitive Transcranial Magnetic Stimulation']}
- {'type': 'OTHER', 'name': 'Motor Control Exercises', 'description': "The rehabilitation program will consist of a 30-minute session of motor control exercises following the rTMS (Active or Sham) intervention. This approach aims to improve spine health through the optimization of spine loading. The first session will be preceded by an individualized evaluation of the participant's abilities and deficiencies to tailor the training program to each participant.", 'armGroupLabels': ['Active rTMS + Motor control exercises', 'Sham rTMS + Motor control exercises']}

Primary Outcomes:
- {'measure': 'Pain intensity (average pain over the last week)', 'description': 'Pain score on a 11-point pain numerical rating scale (PNRS) ranging from 0 to 10, with 0 meaning no pain and 10 the worst pain imaginable.', 'timeFrame': 'Change from baseline to 4 weeks, 8 weeks, 12 weeks and 24 weeks'}

Please estimate the sample size based on the assumption: 
alpha of 0.05, beta of 0.20, and 20% dropout rate
Sample size
        Our sample was estimated using the CID for pain intensity (2 points)30 and the standard deviation reported from a study that used a combination of transcranial direct current stimulation and exercise (3.0).58 Considering an alpha of 0.05, a beta of 0.20 and 20% of dropout, a sample size of 140 participants (35 per group) was calculated using G*Power V.3.1.9 software.