This study plans to learn more about how the energy system works in girls with Turner syndrome. This is important to know so that the investigators understand how Turner syndrome relates to diseases such as diabetes, extra weight gain, heart disease and liver disease, and how this impacts day to day life.

Inclusion Criteria:

• Female
• Age 12-21 years
• 45,XO karyotype in >50% of cells tested with a diagnosis of Turner syndrome (TS)
• Tanner stage 2-5 for breast development

Exclusion Criteria:

• Growth hormone treatment within the past 3 months
• Diagnosis of type 1 or type 2 diabetes
• Untreated hypertension with blood pressure > 99%ile for sex, age and height or >140/90
• Weight > 300 lbs
• Height < 54"
• Aortic sinus of Valsalva or ascending aorta z-score > 2
• Other cognitive, psychiatric, or physical impairment resulting in inability to tolerate the study procedures, including vigorous exercise
• Pregnancy

Investigators will enroll adolescent and young adult females with Turner syndrome who will complete all study procedures. One parent will also be enrolled (either mother or father) to complete questionnaires about the daughter.