Evaluate the collective function of references cited together in a given text segment.
Classify their combined role into one of the following categories: 'method', 'background', or 'result'.

Text:Myostatin not only plays a prominent role as negative regulator of skeletal muscle size during physiological pre- and postnatal growth, but also during disease in adult life, when its expression is induced in cardiac or skeletal muscle of rodents with heart disease or cancer as well as in patients with cardiomyopathy, chronic obstructive pulmonary disease and some selected forms of cancer [5-13].
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