Military performance depends on high-level cognition, specifically executive function (EF), while simultaneously performing strenuous exercise. However, most studies examine cognitive performance following, not during, exercise. Therefore, our aim was to examine the relationship between EF and exercise intensity. Following familiarization, 13 Reserve Officers' Training Corp cadets (age = 19.6 + 2 yr, five women) completed a graded exercise test (GxT) and two executive function exercise tests (EFETs) separated by a duration of >24 h. The EFET was a combined iPad-based EF test (Cedar Operator Workload Assessment Tool) and GxT. Heart rate (HR) and prefrontal cortex (PFC) oxygenation [near-infrared spectroscopy (NIRS)] were continuously recorded. The EF score was analyzed for accuracy of responses (%hit rate). Heart rate reserve was calculated to normalize exercise intensity (%HRR). For PFC oxygenation recordings, NIRS variables were used to calculate the tissue saturation index (%TSI). Data from EFET trials were averaged into a singular response. The %hit rate declined at heart rate reserves (HRRs) of >80%, reaching nadir at 100% HRR (74.09 + 10.63%, P < 0.01). The tissue saturation index (TSI) followed a similar pattern, declining at >70% of HRR and at a greater rate during EFET compared with during GxT (P < 0.01), reaching a nadir in both conditions at 100% HRR (60.39 +2.94 vs. 63.13 + 3.16%, P < 0.01). Therefore, EF decline is dependent on exercise intensity, as is %TSI. These data suggest that reductions in EF during high-intensity exercise are at least in part related to attenuated PFC oxygenation. Thus, interventions that improve PFC oxygenation may improve combined exercise and EF performance.