Increased functional capacity of major organ systems improves the quality of life and contributes to reductions in the morbidity associated with chronic debilitating diseases. Routine endurance tests can be used to gauge the progression of disease and the impact of therapeutic modalities in disorders with multiple organ system involvement such as with Mucopolysaccharidosis type VI (MPS VI). MPS VI is a progressive disorder affecting multiple organs and tissues due to the deficient activity of N-acetylgalactosamine-4-sulfatase leading to the accumulation of glycosaminoglycan (GAG) dermatan sulfate. Since 2005, enzyme replacement therapy (ERT) with human recombinant N-acetylgalactosamine-4-sulfatase (galsulfase) has been an available treatment option for MPS VI. These patients are routinely evaluated for extent of disability, disease progression and the impact of ERT. Evaluations are made by a combination of urinary GAG measurement and submaximal intensity endurance tests such as the 3-minute stair climb (3-MSC), and the 6- and 12-minute walk tests (6-MWT and 12-MWT). This review highlights the clinical validity of endurance measures as inexpensive diagnostic tools for diseases affecting multiple organ systems and evaluating the impact of therapeutic modalities, such as ERT for MPS VI.