Here is the design of a clinical trial:

Official Title: Impact of a Physical Activity Program on Bone Mineral Density (BMD) in Children / Adolescents With Chronic Inflammatory Bowel Disease (IBD): Crohn's Disease, Ulcerative Colitis, Unclassified Chronic Colitis

Included conditions:
- Crohn's Enteritis
- Crohn Disease
- Ulcerative Colitis
- Chronic; Colitis (Noninfective)

Study Armgroups:
- {'label': 'physical activity program', 'type': 'EXPERIMENTAL', 'description': 'Child with an adapted physical activity program', 'interventionNames': ['Other: adapted physical activity']}
- {'label': 'Usual care', 'type': 'OTHER', 'interventionNames': ['Other: Usual care']}

Interventions:
- {'type': 'OTHER', 'name': 'Usual care', 'description': 'Patients included in the control group will not benefit from the intervention in adapted physical activity. However, this will not affect their support. Patients will be seen by their specialist doctor as part of the usual management of their IBD.', 'armGroupLabels': ['Usual care']}
- {'type': 'OTHER', 'name': 'adapted physical activity', 'description': 'Patients in the experimental group will have, in addition to their usual follow-up with their specialist doctor, an intervention in adapted physical activity at home, at the rate of 3 sessions (of a duration of 10 to 20 minutes) per week during 9 consecutive months.', 'armGroupLabels': ['physical activity program']}

Primary Outcomes:
- {'measure': 'Change in total (whole body) Bone Mineral Density', 'timeFrame': 'At 9 months'}

Please estimate the sample size based on the assumption: 
To detect this effect size, with a two-sided test at the 0.05 level of significance, a power of 80%, an SD of 0.1 (assuming a correlation of 0.5 between baseline and 9-month follow-up values) with 36 subjects per group will be required. To account for an anticipated rate of 10% of missing data (loss to follow-up), we plan to include a total of 80 subjects (40 per arm).
Sample size calculation
        Based on the literature, we expect a mean whole-body BMD value at inclusion of 0.645Â±0.1âg/cm2 in our study population, and annual variation of 4.4% yielding to an expected mean value of 0.666Â±0.1âg/cm2 at the end of the 9-month study in the control group (ie, a mean change from baseline of 0.021).44 We assume that the mean whole-body BMD value after the 9-month PA training period will be higher than 10% of control group values, corresponding to a whole-body BMD value of 0.733âg/cm2 (ie, a mean change from baseline of 0.088). To detect this effect size, with a two-sided test at the 0.05 level of significance, a power of 80%, an SD of 0.1 (assuming a correlation of 0.5 between baseline and 9-month follow-up values) with 36 subjects per group will be required. To account for an anticipated rate of 10% of missing data (loss to follow-up), we plan to include a total of 80 subjects (40 per arm). As a conservative approach, the sample size calculation did not take into account the adjustment for baseline values.