The heart is a muscle and like other muscles, work makes it stronger and more efficient. Exercise triggers a series of bodily processes that play separate but interconnected roles by stimulating the heart to increase its efforts to pump oxygen-rich blood to the muscles most in need of extra nourishment.
The Heart's Function
All the body's tissues need a constant supply of oxygen and the heart's job is to keep blood, the carrier of that oxygen, moving. The left side pumps oxygenated blood out the aorta and into the circulatory system while the right side pumps oxygen-depleted blood to the lungs, where it receives a fresh infusion, then back again. Blood flow is controlled by valves that open and close and the widening and narrowing of blood vessels. Heart rate refers to the number of beats per minute and stroke volume the amount of blood ejected by the heart with every beat. At rest, the heart beats about 60 times or less per minute and stroke volume is typically about 70 ml per beat.
Adrenal Glands Release Hormones
The adrenal glands on top of the kidneys secrete hormones into the blood that influence the activity of other organs. One of the most powerful hormones is epinephrine, also known as adrenaline. When a signal is sent out from the sympathetic nervous system that exercise is about to begin, the adrenal glands instantly step up production of adrenaline, stimulating an increase of both heart rate and stroke volume and prompting the liver to release stored sugar to give muscles additional energy. Even thinking about exercise starts an "anticipatory" adrenaline release.
Respiratory System Responds
In order to supply the skeletal muscles with the increased amount of oxygenated blood they need, the respiratory system must take in more air. As exercise becomes more strenuous, more adrenaline is released, relaxing and widening the airways. Breathing becomes faster and deeper, and body temperature, blood pressure and metabolic rate all increase, helping blood to move faster through the circulatory system and be directed to the muscles in greatest need.
The Heart Beats Faster to Keep Up
To keep up with the demands of the skeletal muscles and respiratory system, the heart has to work much harder during exercise than it does at rest, its increased effort reflected by a corresponding increase in the number of heartbeats per minute. How fast the heart should beat varies according to age and fitness level but to get optimum benefits without overstraining the heart, the American Heart Association recommends monitoring heart rate to ensure that you stay within your safety zone. In general, your maximum heart rate equals 220 minus your age, and your target rate should not exceed 50 to 85 percent of that. Therefore, the maximum heart rate for a 50-year-old would be 170 beats per minute, and the safe range during exercise from 85 to 145 beats per minute. If you can exercise and talk at the same time, you're probably within your safety zone, the AHA says, but if not, or you get out of breath too quickly, you're likely overexerting yourself -- and your heart. See Resources for more information on monitoring heart rate.
Member Comments