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:The magnitude of muscle hypertrophy can be variable between-individual components of a muscle group (Narici et al., 1989, 1996; Housh et al., 1992; Norrbrand et al., 2008).
Category: