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:It has previously been shown that recovery VO2 kinetics are adequately characterized by a mono-exponential function following steady-state exercise at “moderate” and “heavy” exercise intensities (Ozyener et al. 2001; rossiter et al. 2002).
Category: