The FitMáx© questionnaire was developed in response to the need for a simple, reliable, and clinically applicable method to estimate cardiorespiratory fitness (CRF) when a cardiopulmonary exercise test (CPET) is unavailable or not practical to perform. CRF, usually expressed as VO₂peak, is an important predictor of health, functional capacity, and treatment outcomes. Despite its clinical relevance, this parameter is still often not assessed in routine care due to the equipment, expertise, and time required.