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

Abstract

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 ΔO2Hb and ΔHHb 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, O2Hb and HHb 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, O2Hb but not HHb or tHb, 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.