The effect of physical conditioning on skeletal muscle of individuals with spinal cord injuries (SCI) has been investigated. The anterior portion of the deltoid muscle (active in wheel-chair propulsion) of untrained and endurance-trained paraplegics and tetraplegics, as well as that of untrained able-bodied subjects, was studied. The characterization involved fibre type distribution, capillarization, fibre areas and also oxidative and glycolytic enzyme levels. A general trend towards a successively higher proportion of type I fibres and lower proportion of type IIB fibres was noted in the order of able-bodied subjects (type I, 42%; type IIB, 41%, n = 8), paraplegics (type I, 57%; type IIB, 13%, n = 13) and tetraplegics (type I, 74%; type IIB, 4.5%, n = 11). The trained SCI groups had significantly higher levels of the citric acid cycle marker enzyme citrate synthase (34% and 63%) than the untrained SCI groups and able-bodied subjects, respectively. The glycolytic marker enzyme 6-phosphofructokinase was 32% lower in the tetraplegic groups than in the other groups. In contrast, the fatty acid oxidation marker enzyme 3-hydroxyacyl-CoA dehydrogenase was markedly higher in the tetraplegic group than in the able-bodied subjects (58%) and tended to be higher (21%, P < 0.1) than in the paraplegic group. The trained SCI groups displayed significantly higher (28%) levels of capillaries per fibre than the untrained SCI groups, which had about the same levels as the untrained able-bodied subjects. It is concluded that several of the findings are in line with normal muscular adaptation, whereas others are unexpected and support a hypothesis that some of the findings might be due to differences between the groups in, for instance, hormone levels or in types of muscular load.