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:The soldiers actively exercised for ten hours per night continuously (alternate marching and running, on a difficult terrain, carrying personal equipment weighting 60% of body weight - estimated intensity of 35–45% of mean VO2 max [15]), slept for four hours (during the day) and performed sedentary activities during the rest of the day.
Category: