There is a progressive loss of muscle strength, muscle mass and muscle quality with advanced age, which results in a condition known as sarcopenia. In this review, the authors outline the magnitude of these losses, their functional consequences, and the efficacy of strength training (ST) as an intervention strategy for delaying, preventing or reversing the effects of sarcopenia. The question of whether sex differences and genetics influence the effects of sarcopenia and responses to ST are also discussed. Although many potential mechanisms for sarcopenia exist, their specific contributions are still unknown. Nevertheless, proposed mechanisms of sarcopenia are outlined and, where information is available, we examine the effects of ST on these potential mechanisms, which include neurogenic factors, anabolic hormones, protein synthesis, gene expression, muscle morphology, and muscle regeneration. Finally, the potential impact of genetics in the muscle response to both sarcopenia and ST is discussed. The evidence presented suggests that ST is an effective intervention for improving strength, muscle mass and muscle quality and delaying the onset of physical disability in the elderly. However, sex differences and genetic factors may play an important role in determining the muscular response to aging and ST.