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:Each participant underwent four static stretching exercises designed to stretch the leg extensor muscles of the dominant limb, according to the procedures of Cramer et al. (2004a, 2005) and Nelson et al. (2001b).
Category: