When you are about begin exercising, your heart rate will likely increase before you begin moving. The phenomenon is called the ‘anticipatory rise’.
The anticipatory rise is the mind’s response to the body’s need to prepare for exercise. Subconsciously, the body knows it is about to exercise and therefore the brain sends several signals in the form of neurotransmitters (e.g. noradrenaline) and hormones (e.g. adrenaline) to the heart. When these chemicals reach the heart they signal for a reduction in parasympathetic drive (taking the brakes off the heart rate) and small increase in sympathetic drive (pressing down on the accelerator), resulting in an increased heart rate.
The increase in heart rate is important because it leads to an increase in cardiac output (the amount of blood pumped out of the left side of the heart in one minute). This is turn results in an increased blood supply to the body. At the same time the body begins redirecting the blood supply to the parts of body that will require it during the exercise. This increased blood supply brings with it oxygen and an increased ability to produce energy in the muscles, which will be used to as fuel for exercise.
The anticipatory rise is the body’s pre-warm up before you physically start warming up. It helps you adapt to the forthcoming exercise quicker and more efficiently. The better your cardiovascular health, the more adept your body will become at honing this response. You will be able to do more in each session and further improve your performance… a truly virtuous circle.