UNDERSTANDING THE EFFECTS OF PULMONARY ARTERIAL HYPERPTENSION ON LEAN MUSCLE MASS-SUBSTUDY

After completion of the Baseline study visit for the main study (MUSCLE UP-PH), participants at the University of Pennsylvania location will be invited to participate in an optional substudy. The substudy will implement a low-load resistance exercise training for the lower extremities, focusing primarily on the gastrocnemius muscles. The goal of this intervention is to understand how low-load resistance training will impact blood flow and oxygen tissue extraction on the lower legs.

Inclusion Criteria: Participating the main MUSCLE UP Study: * Signed informed consent prior to initiation of any study mandated procedure. * Male and female patient's ≥ 18 years of age. * Diagnosis of PAH belonging to one of the following subgroups of Group 1 PH according to the updated clinical classification \[Humbert 2022\] * Idiopathic (IPAH) * Heritable (HPAH) * Drugs or toxins induced * Associated (APAH) with one of the following: * Connective tissue disease; * Human immunodeficiency virus (HIV) infection; * Congenital heart disease; or * Portopulmonary hypertension * Diagnosis of PAH within 6 months of enrollment or diagnosis of PAH and on stable therapy for 3 months prior to enrollment * Documented hemodynamic diagnosis of PAH by right heart catheterization (RHC), prior to enrollment showing: * mPAP \> 20 mmHg; and * PAWP or LVEDP ≤ 15 mmHg * PVR \> 2 Wood units Exclusion Criteria: * Prior to enrollment, evidence of moderately severe obstructive ventilator defect with: * FEV1/FVC ≤ 5th percentile; and * FEV1 z-score \< -2.5 * Prior to enrollment, evidence of severe restrictive defect with * TLC \< 5th percentile * FEV1 z-score \< -4 * More than moderate aortic or mitral valve disease * LVEF \< 40% within 1 year of screening * Pregnancy