Purpose Fat free mass (FFM) is considered the metabolically active component of human body and is positively associated with maximal oxygen uptake ( $${\text{VO}}_{2} {\text{max}}$$ VO 2 max ). However, FFM is composed of metabolically active and inactive subcomponents whose proportion can vary depending on body composition and clinical condition, possibly affecting such association. Although it is known that in facioscapulohu...