Skeletal muscle metabolism, morphology and function in sedentary smokers and nonsmokers.

Smokers and nonsmokers of a homogeneous population of sedentary men have been compared with respect to skeletal muscle (vastus lateralis) morphological, metabolic and functional characteristics. The percentage type I fibres was lower and that of type IIB fibres higher in the smokers. Fibre areas were almost equal in the two groups. Muscle oxidative capacity was lowered in the smokers, as judged from decreased mitochondrial enzyme activities and a lowered fibrillar space mitochondrial volume fraction. Isometric and dynamic strengths were lower in the smokers, except at the highest velocity of movement studied. Dynamic strengths expressed in relation to isometric strength were similar at all velocities except the highest, where the smokers were relatively stronger. Muscular endurance, measured in short-term isometric and dynamic tests, was not different. It is suggested that the lowered muscle oxidative capacity and strength in the smokers may be partly a consequence of the different fibre type distribution. A possibly lower physical activity level, and tobacco smoke constituents (e.g. carbon monoxide) may also be instrumental. It is not clear whether the different fibre type distribution in the smokers is an effect of smoking per se, or if background factors are responsible.