If your child is eligible and you allow them to join the study, they will:

• Come in for a visit to make sure they are eligible to join (V1). They will then complete a screening period which lasts about 2-3 weeks and includes using a PrO2 breathing device and wearing an activity watch and patch.
• Come in for a 2nd visit (V2) and get a random assignment (fair, equal chance) to 1 of 3 levels of resistance breathing exercises (high, low, or no resistance). For about 8 weeks, your child will perform breathing exercises with the PrO2 device 3 times per week at the assigned level of resistance and continue to wear the activity watch and patch.
• Have a phone call with a study team member to see how they are doing (V3) and come in for the last visit at 8 weeks (V4).
• Have phone calls with the team at 2 and 6 weeks of doig the breathing exercies.

At all study visits, your child will complete questionnaires, perform breathing exercises, and physical activity tests.