"FUTILE CYCLING" IN PHYSIOLOGIC CONTROL SYSTEMS: A PRICE PAID FOR FINE CONTROL.

The article studies futile cycling in physiologic control system. Substrate cycling refers to the simultaneous occurrence of opposing reactions at different rates. It is described as allowing fine tuning of metabolism. In the study, researchers drew an analogy between substrate cycling in metabolic pathways and tonic activity in opposing neural systems and applied it to the case of heart rate (HR) regulation by the two limbs of the autonomic nervous system. They concluded that the physiologic advantage of which cycling occurs is that fine HR modulation around the baseline value could be achieved faster, simultaneously and reciprocal changes in activity in two systems. The other assumptions made are that sympathetic and vagal systems for HR modulation are equipotent.