Hemodynamic data for all participants (Control - black line, POTS - grey line) before and during a 10 min 70° head-up tilt. Heart Rate (HR) is expressed as beats per min (bpm), Mean Arterial Pressure (MAP) as millimeters of mercury (mmHg), Cardiac Output (CO) as liters per minute (L · min-1), and Total Peripheral Resistance (TPR) as millimeters of mercury per liter per minute (mm Hg · L · min-1). * indicates difference from control, P < 0.05. # indicates overall effect different from control, P < 0.05.