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:Exercise subjects performed flywheel resistance exercise in the 6 head down position (Alkner et al 2007; Trappe et al. 2007) every third day, plus 40-min supine treadmill exercise within LBNP (Macias et al. 2007) 3‚Äì4 days per week with interspersed rest days.
Category: