“Having an extremely low body-fat percentage can affect the cardiovascular system’s ability to function normally,” says cardiologist Kevin Campbell , ., fellow of the American College of Cardiology. For example, in one study published in the International Journal of Sports Physiology and Performance , when bodybuilders prepared for competition by lowering their body fat, their heart rate dropped to 27 beats per minute. Too low heart rates, called bradycardia, can lead to dizziness, passing out, and cardiac arrest. Meanwhile, other electrolyte imbalances due to too-low of a body fat percentage, not to mention caloric intake, can lead to “cardiac arrhythmias and sudden cardiac death, he says.
The heart and blood vessels comprise the two elements of the cardiovascular system that work together in providing nourishment and oxygen to the organs of the body. The activity of these two elements is also coordinated in the body's response to stress. Acute stress — stress that is momentary or short-term such as meeting deadlines, being stuck in traffic or suddenly slamming on the brakes to avoid an accident — causes an increase in heart rate and stronger contractions of the heart muscle, with the stress hormones — adrenaline, noradrenaline and cortisol — acting as messengers for these effects. In addition, the blood vessels that direct blood to the large muscles and the heart dilate, thereby increasing the amount of blood pumped to these parts of the body and elevating blood pressure. This is also known as the fight or flight response. Once the acute stress episode has passed, the body returns to its normal state.