While the myosin heavy chain (MHC) isoform content allows to explain a great part of the heterogeneity of the muscle contractile properties, single fibres still exhibit a functional variability, independently of the MHC isoform expressed. Additionally, the mechanical characteristics of a given fibre type has been shown to be altered by physiological conditions. This study compares the mechanical properties of human single muscles fibres following long-term unweighting to those with normal functioning. Biopsies were obtained from the vastus lateralis of 5 individuals with chronic (>3 years) spinal cord injury (SCI) and 10 able-bodied controls (CTRL). The skinned single muscle fibre model was coupled with electrophoresis analyses to investigate the functional adaptations of the contractile apparatus to the absence of normal weight bearing activities. The expected decrease of maximal fibre force was not observed following long-term unweighting, as no statistical difference was found between the control and SCI group. However, maximal unloaded shortening velocity was greater in type IIa, IIa/IIx and IIx fibres (by 26%, 65% and 47%, respectively, P<0.01) of the SCI group. As a result, fibre peak power was higher in type IIa (46%) and IIa/IIx fibres (118%), and normalized peak power was increased by 70% in type IIa/IIx fibres (P<0.05). Fibre Ca²⁺ sensitivity and passive properties were not affected in paralysed muscles. Fibres from long-term unloaded muscles have greater performance characteristics, which contrasts with results from short-term unweighting studies.