Comparative Effects of Acute HIIE and MICE on Executive Function, Prefrontal Oxyhaemoglobin Responses, and Related Biomarkers in Sedentary Young Adults: A Randomized Crossover Trial

Background/Objectives: To compare the acute effects of high-intensity interval exercise (HIIE) and moderate-intensity continuous exercise (MICE) on executive-function performance, prefrontal oxyhaemoglobin (Oxy-Hb) signals, brain-derived neurotrophic factor (BDNF), and lactate in sedentary young adults. Methods: Fifteen participants (10 men, 5 women; 22 ± 2 years; BMI 23.07 ± 4.12 kg/m2) completed HIIE, MICE, and seated control sessions in randomized order with 7-day washouts. Stroop, N-back, and Switching tasks; prefrontal fNIRS; plasma BDNF; and blood lactate were assessed before and after each condition. Correlation and indirect-effect analyses were exploratory. Results: Both HIIE and MICE significantly improved inhibitory control, working memory, and cognitive flexibility relative to baseline. For inhibitory control, both exercise modes reduced reaction times in congruent and incongruent Stroop tasks, but only HIIE improved Stroop interference performance. Both HIIE and MICE improved inhibitory control, working memory, and cognitive flexibility relative to baseline. Both reduced reaction times in the congruent and incongruent Stroop, 3-back, and Switching trials, whereas only HIIE improved Stroop interference. Both exercise modes increased Oxy-Hb in the OFA during Stroop and in the FPA and R-DLPFC during Switching. HIIE additionally increased Oxy-Hb in the FPA during Stroop, PTR during Switching, and R-DLPFC during N-back. Both exercise modes increased circulating BDNF and lactate, with a greater lactate response after HIIE. Improvements in executive function were associated with changes in Oxy-Hb, BDNF, and lactate. Conclusions: Both exercise sessions were followed by faster reaction times on selected tasks. The small sample, multiple analyses, and potential systemic contributions to fNIRS signals preclude firm conclusions about exercise-mode superiority or biological mediation.