An increased heart rate, also known as tachycardia, is a heart rate that's beyond the normal range for a typical resting heart rate. Resting heart rates are the number of times per minute that your heart beats while you're at rest or sleeping. Numerous factors can cause heart rates to increase, although some factors are more dangerous than others and signal underlying health problems. Activity level, stress and air temperature, among other factors, increase heart rate.
In response to exercise, both aerobic and strength training, your heart rate increases. As the physiological demands of the activity increase, so too does heart rate. The heart beats faster during exercise to pump more blood to the working muscles. The blood delivers oxygen and nutrients to the tissues and removes problematic metabolic byproducts from the cells. According to the American Heart Association, a person's maximum achievable heart rate through exercise roughly corresponds to the formula 220 minus age, although this formula is not accurate for every individual.
According to the Cleveland Clinic, elevated heart rates are a natural response to stress. Excessive stress in your life can invoke the fight-or-flight reaction, which is the body's natural alarm system. When you face real or perceived threats to health or safety, the brain's hypothalamus region is stimulated, which produces nerve and hormonal signals that act on the adrenal glands. During stressful situations, the adrenal glands, which sit on top of the kidneys, release significant amounts of hormones, especially adrenaline and cortisol. These two hormones work in concert to ready the body for action. Adrenaline boosts your heart rate, along with blood pressure and energy supplies, while cortisol mobilizes stored sugars, increases the brain's use of glucose and down-regulates nonessential bodily functions, among other activities. Chronic activation of the body's stress-response system increases the risk of health problems, including heart disease, digestive problems and depression.
Heat stress can increase your heart rate, and, if severe and prolonged, can cause significant health problems. According to the Canadian Centre for Occupational Health and Safety, in moderately hot environments, your body vents heat by increasing the heart rate and pumping more blood to the surface. When blood is sent to the surface or skin, excess body heat is lost to the environment and you begin sweating. Alterations in your blood flow, along with excessive sweating, affect your ability to perform physical and mental work. Physical work generates additional metabolic heat, which compounds the body's heat burden. Dehydration, which often accompanies heat stress, results in decreased blood volume. Because the total blood volume is lower, the body must increase the heart rate to keep the blood flow to the essential tissues and organs constant.
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