Here is the design of a clinical trial:

Official Title: Exercise Therapy for Osteoarthritis Pain: How Does it Work?

Included conditions:
- Knee Osteoarthritis

Study Armgroups:
- {'label': 'Muscle Strengthening Training (MST)-group', 'type': 'EXPERIMENTAL', 'description': 'Subjects allocated to the MST group (n=30) will perform a muscle strengthening training program of 12 weeks.', 'interventionNames': ['Other: Muscle Strengthening Training']}
- {'label': 'Behavioral Graded Activity (BGA)-group', 'type': 'EXPERIMENTAL', 'description': 'Subjects allocated to the BGA group (n=30) will perform a rehabilitation program according to the principles of behavioural graded activity for a period of 12 weeks.', 'interventionNames': ['Behavioral: Behavioral graded activity']}
- {'label': 'Control group', 'type': 'NO_INTERVENTION', 'description': 'Subjects allocated to the control group (n=30) have to maintain their current life-style and treatment (if any) and to refrain from other new interventions during 24 weeks.'}

Interventions:
- {'type': 'OTHER', 'name': 'Muscle Strengthening Training', 'description': 'Muscle strengthening training will take place for a period of 12 weeks, in which participants will have 36 exercise sessions (18 at the hospital under supervision of a physiotherapist; 18 unsupervised at home) planned. Muscles of the leg (i.e. quadriceps, hip ab- and adductors) will be trained at 3 set of 10 repetitions at 80% of 1RM with the use of elastic bands. 1RM will be assessed at baseline and the exercise intensity will be progressively increased by 10% of 1RM every two sessions from 50 up to 70-80 % of 1RM. Every 6 sessions, the 1RM will be reassessed and the training resistances will be adapted.', 'armGroupLabels': ['Muscle Strengthening Training (MST)-group']}
- {'type': 'BEHAVIORAL', 'name': 'Behavioral graded activity', 'description': "Subjects will receive a behavioural treatment integrated within the concepts of operant conditioning with exercise therapy for a period of 12 weeks, in which the subjects will have maximum 36 BGA sessions (min. 13- max. 18 at the hospital under supervision of a physiotherapist; 18 unsupervised at home) planned. The purpose of BGA is to increase the level of activities in a time-contingent manner and increase the level of physical activity in the subject's daily lives. BGA consists of 3 phases: pain education (phase 1), treatment phase in which subjects increase their level of activity gradually (phase 2) and integration of learned principles in daily live (phase 3).", 'armGroupLabels': ['Behavioral Graded Activity (BGA)-group']}

Primary Outcomes:
- {'measure': 'Knee pain as primary study outcome', 'description': 'Pain is the primary outcome as it is the primary and most disabling symptom in OA. The pain subscale of the WOMAC Osteoarthritis Index LK3.0 questionnaire will be used for the assessment of pain severity. The Knee injury and Osteoarthritis Outcome Score (KOOS) includes WOMAC Osteoarthritis Index LK3.0 in its complete and original format (with permission). WOMAC (and therefore the pain and symptoms subscale of the KOOS) is a valid tool for subjects with KOA. The KOOS is proven to generate valid and reliable scores.', 'timeFrame': 'Baseline'}
- {'measure': 'Knee pain as primary study outcome', 'description': 'Pain is the primary outcome as it is the primary and most disabling symptom in OA. The pain subscale of the WOMAC Osteoarthritis Index LK3.0 questionnaire will be used for the assessment of pain severity. The Knee injury and Osteoarthritis Outcome Score (KOOS) includes WOMAC Osteoarthritis Index LK3.0 in its complete and original format (with permission). WOMAC (and therefore the pain and symptoms subscale of the KOOS) is a valid tool for subjects with KOA. The KOOS is proven to generate valid and reliable scores.', 'timeFrame': 'during intervention: week 2 (acute)'}
- {'measure': 'Knee pain as primary study outcome', 'description': 'Pain is the primary outcome as it is the primary and most disabling symptom in OA. The pain subscale of the WOMAC Osteoarthritis Index LK3.0 questionnaire will be used for the assessment of pain severity. The Knee injury and Osteoarthritis Outcome Score (KOOS) includes WOMAC Osteoarthritis Index LK3.0 in its complete and original format (with permission). WOMAC (and therefore the pain and symptoms subscale of the KOOS) is a valid tool for subjects with KOA. The KOOS is proven to generate valid and reliable scores.', 'timeFrame': 'during intervention: week 10 (acute)'}
- {'measure': 'Knee pain as primary study outcome', 'description': 'Pain is the primary outcome as it is the primary and most disabling symptom in OA. The pain subscale of the WOMAC Osteoarthritis Index LK3.0 questionnaire will be used for the assessment of pain severity. The Knee injury and Osteoarthritis Outcome Score (KOOS) includes WOMAC Osteoarthritis Index LK3.0 in its complete and original format (with permission). WOMAC (and therefore the pain and symptoms subscale of the KOOS) is a valid tool for subjects with KOA. The KOOS is proven to generate valid and reliable scores.', 'timeFrame': 'post-intervention: week 13'}
- {'measure': 'Knee pain as primary study outcome', 'description': 'Pain is the primary outcome as it is the primary and most disabling symptom in OA. The pain subscale of the WOMAC Osteoarthritis Index LK3.0 questionnaire will be used for the assessment of pain severity. The Knee injury and Osteoarthritis Outcome Score (KOOS) includes WOMAC Osteoarthritis Index LK3.0 in its complete and original format (with permission). WOMAC (and therefore the pain and symptoms subscale of the KOOS) is a valid tool for subjects with KOA. The KOOS is proven to generate valid and reliable scores.', 'timeFrame': 'post-intervention: week 26'}
- {'measure': 'Knee pain as primary study outcome', 'description': 'Pain is the primary outcome as it is the primary and most disabling symptom in OA. The pain subscale of the WOMAC Osteoarthritis Index LK3.0 questionnaire will be used for the assessment of pain severity. The Knee injury and Osteoarthritis Outcome Score (KOOS) includes WOMAC Osteoarthritis Index LK3.0 in its complete and original format (with permission). WOMAC (and therefore the pain and symptoms subscale of the KOOS) is a valid tool for subjects with KOA. The KOOS is proven to generate valid and reliable scores.', 'timeFrame': 'post-intervention: week 64'}

Please estimate the sample size based on the assumption: 
Expected correlation over time of 0.3, type I error of 0.025, type II error of 0.2, and a 20% loss to follow-up.
Sample size
        Sample sizes were calculated to detect a clinically relevant difference between the treatment arms and the control of 0.49 (0.39 to 59). The effect size is based on results from a recent Cochrane meta-analysis (including 44 studies, 3537 participants).7 Because for each patient three measurements are obtained (at 0, 12 and 26 weeks), the effect size is transformed into an F-test statistic of 0.245 to be used within a sample size calculation for repeated measures analysis of variance. A sample size of 24 per treatment arm is obtained with an expected correlation over time of 0.3, allowing for a type I error of 0.025 and a type II error of 0.2. A 20% loss to follow-up is expected based on earlier studies and is added so that the total required sample size is estimated at 30 patients per study arm, resulting in 90 KOA patients to be recruited.