Hematopoietic stem cell transplantation is a treatment used to restore blood cell function in diseases of myeloid and lymphoid origin, which can be malignant or non-malignant. There are two types: autologous transplantation, which uses the patient's own stem cells, and allogeneic transplantation, which uses stem cells from a donor after a high-dose chemotherapy and radiotherapy preparation. This process can lead to complications such as immune reactions, infections, and organ toxicity, affecting the cardiovascular, musculoskeletal, and nervous systems. These complications often reduce physical activity, muscle strength, lung function, and quality of life. Before transplantation, it is important to assess patients' comorbidities, functional status, and physical fitness to evaluate their ability to tolerate treatment and risk of complications. Low exercise tolerance and impaired physical function are linked to poorer outcomes. Objective tests of physical function provide valuable information about health status. Pre-transplant muscle strength and cardiopulmonary fitness influence post-transplant recovery, so comprehensive assessments are necessary. Physiotherapy and rehabilitation support patients by preparing them for treatment, maintaining health during therapy, improving physical function after treatment, and enhancing quality of life in palliative care. Exercise improves functional capacity, quality of life, and daily activities, but symptoms like fatigue, pain, breathlessness, and muscle weakness, as well as other barriers, may limit participation. Physical fitness is the body's ability to perform daily activities efficiently. Reduced fitness leads to frailty and decreased function, which are associated with increased treatment toxicity and mortality. Although the importance of physical fitness before transplantation is recognized, data from objective measurements are limited. Common pre-transplant assessments include lung function tests, walking tests, handgrip strength, and mobility tests. This study aims to compare the health-related physical fitness of individuals undergoing allogeneic hematopoietic stem cell transplantation with healthy controls.