The aim of this study is to assess whether the 1 minute Sit to Stand (STS) test can be used as a measure of submaximal endurance during a pulmonary exacerbation of Cystic Fibrosis (CF) for patients in the acute care setting. We hypothesize that if the STS test is a valid measure of submaximal cardiovascular endurance, it will moderately correlate with 6 minute walk distance (6MWD).

Inclusion Criteria:

• patients age 6-35 with cystic fibrosis who are admitted for a pulmonary exacerbation and receive ongoing physical therapy throughout their admission.

Exclusion Criteria:

• patients with cystic fibrosis who are under the age of 6,
• patients with cystic fibrosis who are not admitted for a pulmonary exacerbation,
• patients with cystic fibrosis who are not being followed regularly by physical therapy (>5x/week) throughout their inpatient admission,
• patients with cystic fibrosis who are unable to follow instructions for standardized testing,
• patients with cystic fibrosis who are not medically stable to participate in submaximal exercise testing.
• patients whose inpatient admission is anticipated to be <1 week.
• Patients who are readmitted to the hospital within the year will not be included in the study more than once.