Athletes involved in collision sports can sustain up to ~1400 head impacts, within a single season. In this study, we explore the physiological nature of sub-concussive impacts using a calibrated MRI method, which combines hypercapnic and hyperoxic breathing manipulations. Collegiate football players were scanned at pre-season baseline and following three weeks of practices and one game. Relative to baseline, we observed global increased resting oxygen extraction fraction (OEF0) and cerebral metabolic rate of oxygen consumption (CMRO2|0) in the grey-matter, with significant differences found within the frontal lobe (P<0.05). These results emphasize the need to regulate exposure to head impacts in sports.