A human heart beats approximately 45 million times per year, but this can vary based on factors such as age, gender and physical activity level. According to the American Heart Association, a normal heart rate can range between 50 and 100 beats per minute. However, a resting heart rate under 80 beats per minute is considered optimal. Your heart rate has large variability and can change frequently throughout the day. Here are six primary factors that influence heart rate.
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When your body temperature changes, so does your heart rate. This is one of the thermoregulatory changes that occur to prevent the body’s core temperature of 98.6 degrees Farhenheit from increasing or decreasing. Heart rate increases when heat is gained by the body such as in hot climates and during exercise in order to transfer more heat away from the body. When the body loses heat such as in cold weather or a cold shower, heart rate decreases to preserve core temperature.
After you eat a meal, your heart rate increases to aid with digestion. More blood is directed toward the gastrointestinal tract to process the food. When larger quantities of food are consumed, heart rate may be increased for a longer period of time compared to after eating a small meal or snack. Heart rate can rise above 100 beats per minute, reaching a tachycardic rate due to the effects of eating.
During exercise, your heart rate goes up to facilitate the increased demand for oxygen and carbon dioxide removal to and from the muscles. Heart rate can increase two to three times above resting heart rate depending on the intensity and duration of exercise. Exercising on a regular basis can reduce your resting heart rate and is considered a healthy and beneficial adaptation. Drink water before, during and after exercise to prevent dehydration. Being dehydrated can increase your heart rate and place more stress on the heart.
As you age, your resting and daily average heart rate does not change significantly. However, your maximum heart rate decreases as you get older due to the physiological effects of aging, such as telomere shortening and associated deconditioning. Your maximum heart rate can be estimated by subtracting your age from 220.
Women have higher heart rates than men during sleep and when awake. The general consensus for this difference is that women are usually smaller than men and require a faster heart beat to facilitate metabolism. Much of the size difference between men and women is due to women having a less total muscle mass. Because muscle is responsible for much of the body's metabolism, the higher heart rates experienced by women may be a natural compensatory mechanism to turn up the metabolic rate.
Caffeine and Other Drugs
Found in coffee, teas and sodas, caffeine is a stimulant drug that influences the nervous system to increase heart rate. It mimics the effect of adrenaline, a natural hormone in the body responsible for elevating heart rate. Other stimulants such as cocaine and ephedrine work in a similar manner.
On the other hand, there are specific drugs used in lowering heart rate such as beta- and calcium channel blockers. Beta-blockers work by interfering with the receptors that adrenaline binds to, subsequently decreasing hormonal influence on heart rate. Calcium channel blockers reduce the amount of calcium that enters the heart muscle. Because calcium is needed for muscle to contract, the heart beats at a slower rate when this drug is taken.