According to MayoClinic.com, a normal heart rate is between 60 and 100 beats per minute. It is not uncommon for an athlete to have a resting heart rate between 40 to 60 beats per minute. A low resting heart rate may be indicative of a healthy cardiovascular system or it may signal the advent of heart disease. When the heart rate is over 100, it can be indicative of strenuous activity or illness.
In order to keep adequate oxygenation of the muscles when working out, the heart has to beat faster. As the intensity of exercise increases, the respiratory rate increases to bring more oxygen into the system and the heart beats faster in order to transport that oxygen. MayoClinic.com recommends that people not exceed a moderate intensity workout that keeps the heart rate in between 75 and 80 percent of its maximum rate, which contributes to good heart health.
Illness and Fever
Systemic illness can increase the heart rate. Fever increase the body's metabolism as it tries to fight off the disease. Increased metabolism requires increased oxygenation and nutrients, requiring the heart to beat faster. Fever also causes fluid loss through sweating, which is the body's natural way of eliminating excess heat. The heart pumps faster when the body is dehydrated. Drinking plenty of non-alcoholic liquids and using acetaminophen to bring the fever down can help lower the heart rate.
MayoClinic.com states that other factors influence heart rate. Body size has a direct effect on heart rate. The more weight the body has to carry around, the harder the heart has to work to oxygenate the system. Emotions and stress can influence the heart rate. Stressful situations turn on the fight or flight system in the brain, and this increases the heart rate. A meditative, peaceful state of mind can slow the heart rate. Air temperature, medications and body position can also influence heart rate.