The term "sarcopenia" describes the progressive decline of muscle mass, strength 
and function occurring with aging. It is not considered a disease, but the 
direct consequence of the aging process on the skeletal muscle. Multiple 
demographic (e.g. gender, race), biological (e.g. inflammatory status) and 
clinical (e.g. diabetes, metabolic syndrome, congestive heart failure, 
medications) factors are able to influence (positively or negatively) the 
skeletal muscle quality and quantity. The extreme paucity of clinical trials on 
sarcopenia in literature is mainly due to difficulties in designing studies able 
to isolate the aging process from its multiple and interconnected consequences. 
In the present review, we present the major factors to consider as potential 
sources of biased results when evaluating potential candidates for clinical 
trials on sarcopenia. The development of clinical trials exploring the nature of 
the sarcopenia process is urgent, but several controversial issues on this 
hallmark of aging still need clarification.