Cerebral oxygenation and cardiac output responses during short repeated sprints exercise and modulatory effect of glucose ingestion

We studied the time profile of changes (Δ) in cerebral oxyhaemoglobin (O2Hb), deoxyhaemoglobin (HHb) and total haemoglobin (tHb) concentrations during the performance of repeated sprints and its relationship with cardiac output. The modulatory effect of glucose ingestion and acute hyperglycaemia on cerebral haemoglobin responses was also investigated. Ten young male participants performed a set of 10 repeated 6-s sprints on a cycle ergometer after ingesting 70 g of glucose (GLU) or a placebo drink (PLA). Heart rate, stroke volume and cardiac output (impedance cardiography) and ΔO2Hb, ΔHHb and ΔtHb in the frontal region of the cerebral cortex using near-infrared spectroscopy (NIRS) were continuously measured. Each sprint elicited a significant positive O2Hb and HHb response that was similar in the two trials. The magnitude of cerebral haemoglobin changes increased with the number of sprint repetitions and was positively correlated with the increase in cardiac output. After each sprint, ΔO2Hb and ΔHHb rapidly returned to baseline, while cardiac output remained elevated. At the end of the repeated sprints, O2Hb decreased to below pre-exercise values, whereas HHb and tHb were elevated. After 10-15 min recovery, ΔO2Hb but not ΔHHb or ΔtHb, returned to pre-exercise values in the PLA, while in the GLU trial O2Hb increased above pre-exercise values (reactive hyperaemia). We conclude that short sprint exercise induces elevation of O2Hb, HHb and tHb during the sprint exertion in parallel with the increase in cardiac output. However, together with the transient increase in cerebral haemoglobin, a progressive decline in cerebral oxygen saturation develops during the course of the repeated sprints. Glucose ingestion does not alter cerebral haemoglobin responses to the sprint exercise but seems to be associated with a faster recovery of O2Hb. New findings How does cerebral oxy-, deoxy-, and total haemoglobin change during repeated short cycling sprints. Each repeated short sprints produce a transient increase in O2Hb, HHb, and tHb, which is positively correlated with cardiac output. After each sprint, O2Hb, HHb and tHb rapidly return to baseline, despite a still elevated cardiac output. Repeated sprints performance is accompanied with significant decrease in cerebral haemoglobin saturation. Glucose ingestion, although improving performance, does not affect O2Hb, HHb, and tHb responses to the repeated sprint exercise, but seems to enhance recovery of cerebral tissue oxygenation after repeated sprint exercise.