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

In this study we investigated changes in concentrations of cerebral oxyhaemoglobin (O2Hb), deoxyhaemoglobin (HHb), and total haemoglobin (tHb) during repeated sprints and their relationship with cardiac output. We also examined the effect of glucose ingestion and acute hyperglycaemia on cerebral haemoglobin responses. Ten young male participants ingested either a glucose drink (70 g) or a placebo before performing a set of 10 repeated 6-second sprints on a cycle ergometer. Heart rate, stroke volume, and cardiac output were measured continuously using impedance cardiography, while changes in O2Hb, HHb, and tHb in the frontal region of the cerebral cortex were measured using near-infrared spectroscopy (NIRS). The results showed that each sprint elicited a transient increase in O2Hb and to lesser extent HHb concentrations, which was enhanced with the number of sprint repetitions and correlated with cardiac output. After each sprint, O2Hb and HHb quickly returned to baseline, while cardiac output remained elevated. At the end of the repeated sprints, O2Hb was decreased to below pre-exercise levels, while HHb and tHb were elevated. After a recovery of 10-15 min, O2Hb returned to pre-exercise values in the placebo trial, but increased to above pre-exercise values (reactive hyperaemia) in the glucose trial. Our findings suggest that short sprint exercise increases O2Hb, HHb, and tHb levels during exertion in parallel with cardiac output. However, in addition to the transient increase in cerebral haemoglobin, a progressive decline in cerebral oxygen saturation occurs during repeated sprints. Glucose ingestion does not alter cerebral haemoglobin responses to sprint exercise but appears to be associated with faster recovery of O2Hb.