The study will be conducted to determine the effect of aerobic training on sleep problems and pulmonary functions in children with Down syndrome.

The study will be carried out on 30 children with Down syndrome (trisomy 21) of both sexes, with ages ranging from 7 to 12 years old. Children will be recruited from schools for children with special needs. Children will be randomly assigned into two equal groups (control and study groups), 15 for each group. The control group will receive a selected physical therapy program only, while the study group will receive the same selected physical therapy program as the control group in addition to aerobic exercise in the form of treadmill training. The Arabic version of the Children's Sleep Habits Questionnaire (CSHQ) will be used to assess sleep problems, while a handheld spirometer will be used to assess pulmonary functions (forced vital capacity (FVC), forced expiratory volume in 1 second (FEV1), FEV1/FVC ratio, and peak expiratory flow rate (PEFR)) pre- and post-intervention.

Inclusion Criteria:

• Children with Down syndrome (trisomy 21).
• Their ages range from 7 to 12 years old.
• Both sexes will be included.
• Children should be able to understand and follow simple verbal commands or instructions (intelligence quotient (IQ) range: 50-70).
• Children should be able to walk independently.
• Their total scores on the Arabic version of the Children's Sleep Habits Questionnaire (CSHQ) equal 41 or higher.

Exclusion Criteria:

Children will be excluded from the study if they:

• Have visual or hearing defects.
• Have spinal abnormality such as kyphosis and scoliosis.
• Have history of pulmonary infection and surgery of thoracic and abdominal region within the past 6 months.
• Play any specific sport or exercises.
• Have physical activity restrictions.
• Have musculoskeletal disorder.
• Take medications known to affect sleep.