Sarcopenia, characterized by profound muscle atrophy and the loss of contractile function, contributes significantly to the development of frailty and functional impairment in older age. Although present in aging humans, rat models have failed to clearly demonstrate a similar degree of this age-associated loss of muscle mass and function. This investigation compared two models of rats raised specifically for aging studies, the Fischer 344/NNiaHSd (F344/N) and the Fischer 344/NNiaHSd X Brown Norway/BiNia (F344/NXBN), and sought to determine which model provides the most accurate representation of human sarcopenia. We found that aging had no effect on F344/N muscle mass or contractile function in the extensor digitorum longus (EDL) and soleus (SOL). Conversely, in the F344/NXBN model, aging was found to decrease EDL and SOL mass and contractile function. These changes were sufficient to satisfy the proposed criteria for the diagnosis of human sarcopenia based upon muscle mass and contractile function. Results indicate that the F344/NXBN provides a better model of the alterations seen in aging human muscle than the F344/N rat model.