In order to perform physical activity, your muscles require oxygenated blood to circulate at an increased rate. The more oxygen your body needs to perform the exercise, the higher your breathing and heart rate will be. Although you haven't begun to tax your muscles before exercise, your breathing rate will speed up to prepare your body for the increased cardiovascular expenditure.

Anticipatory Response Anticipatory response is the scientific name given to the pre-exercise increase in breathing rate. No matter what form of exercise you're preparing to begin, neurotransmitters, known as epinephrine and norepinephrine, are released due to anticipatory signals from the brain. These transmitters are also known as adrenaline and noradrenaline.

Function Since your body needs oxygen as a constant energy source during exercise, the anticipatory response that elevates your breathing and heart rate before exercise allows you to make the transition from inactivity to high energy output more easily. Your heart responds by increasing blood flow, dilating blood vessels and jumpstarting energy pathways. Because your pre-exercise heart rate is elevated, you shouldn't consider it an accurate measure of your heart rate.

Potential Risks In a 2009 study conducted by French researchers and published in the "European Heart Journal," subjects with the most elevated heart rates prior to exercise indicated an increased risk of sudden cardiac death later in life. According to Dr. Xavier Jouven, this study marked the first time this association had been shown. Researchers were unsure of the long-term implications of their findings, but cautioned that this anticipatory stress could indicate unhealthy heart conditions.

Heart-Rate Training Sudden increases in heart rate can be risky, but you need an elevated heart rate and breathing rate to handle the stress of exercise. You can measure your resting heart rate by taking your pulse for six seconds on the inside of your wrist, then multiplying that number by 10. Once you have your RHR, you can experiment with heart-rate training. Steady-state cardio training usually involves long aerobic workouts for which you keep your heart rate between 50 and 80 percent of your maximum heart rate. Your maximum heart rate can be found by subtracting your age from 220, but this number isn't exact for everyone.