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:…in the time constant of fundamental phase VO2 “off-kinetics” at moderate vs. heavy exercise intensities (Krustrup et al. 2009; Ozyener et al. 2001; rossiter et al. 2002) whereas studies that measured EPOc magnitude and duration to the point at which resting metabolism was restored found that…
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