Attenuated cardiovascular adjustment to sustained static exercise after carbohydrate loading

We examined whether a higher plasma lactic acid (LA) concentration resulting from carbohydrate (CHO)-loading affects the cardiovascular responses to exercise through a greater activation of LA-induced metaboreflex. Before and after CHO-loading, LA concentration, mean arterial blood pressure (MAP), heart rate (HR), cardiac output (CO), rating perceived exertion (RPE), and integrated electromyogram (iEMG) of the vastus lateralis were studied during a sustained static knee extension of single legs in 16 volunteers. The CHO-loading comprised an exhaustive bout of one-legged cycling (73+/-3% of maximal oxygen uptake for 130-160 min) and consuming a low-CHO diet for 2-3 days and a high-CHO diet for the next 3 days. In the leg that performed the exercise (the experimental leg), the LA concentration after CHO-loading was significantly increased, but the magnitude of MAP, HR, and CO responses during static exercise was significantly decreased in parallel with a significant reduction of RPE and iEMG. In the control leg, there were no changes in the variables before and after CHO-loading. These results suggest that the increased LA concentration resulting from CHO-loading did not affect the cardiovascular adjustment to the sustained exercise. Other mechanisms related to the reduction of RPE and iEMG seem to be responsible for the attenuated cardiovascular responses observed in the experimental leg after CHO-loading.