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:Our participants had performed the movements
 only twice during the intervention epoch while in the ‚Äö√Ñ√≤expert‚Äö√Ñ√¥ studies participants had experienced motor training over years (Calvo-Merino et al., 2005, 2006; Haslinger et al., 2005), several days (Reithler et al., 2007) or weeks (Cross et al., 2006).
Category: