Ending the Confusion about how Cardiovascular Exercise affects the Body
For whatever reason, you decide you want to start exercising. Maybe you need to “get healthier” or you are looking for a way to manage your stress, anxiety or depression. Perhaps you want to lose a little weight or build some muscles. The benefits of regular exercise are endless and priceless! But some of you may be apprehensive about starting an exercise program if you have never exercised or its been awhile. If you have a heart defect or any other chronic disease, you may be even more nervous about exercising. Once you understand what exercise does to your body, you will feel more confident to begin and maintain an exercise program that works for you!
Acute effects of exercise– Once you begin some cardiovascular exercise like walking, running, or cycling, your heart rate will immediately increase due to a down regulation of vagus nerve activity to the heart. Be decreasing this vagal tone, your heart rate can quickly increase to approximately 100 beats per minute. The amount of blood returning to the heart will increase and that will mean more blood will be able to exit the heart with each beat. The vagus nerve is part of the parasympathetic nervous system. When you begin to exercise, the sympathetic nervous system up regulates and causes the release of catecholamines which will also help to increase your heart rate to deliver oxygen to your working muscles. Those hormones will also cause some blood vessels to constrict and others to dilate to direct blood to the working muscles. The byproducts of metabolism will help to increase your breathing rate and more surface area of your lungs will be used to get oxygen out of the inspired air and into the blood.
Maybe you would rather perform some resistance exercise. What kinds of effects will that have your body? Resistance exercise causes many of the same demands on the cardiovascular system. However, the increase in heart rate is due not only to decreased vagal tone and increase in catecholamines. When the heart has to push against the resistance of the muscles lifting heavy weights, it decreases the volume of blood the heart can push out with each beat (stroke volume). Thus, when the stroke volume goes down, heart rate must go up to meet the demand of the exercise. All these responses are not only normal, but necessary and your body loves it! So embrace it!
Chronic effects of exercise With consistent exercise the cardiovascular system adapts. The heart muscle becomes stronger and stroke volume goes up and heart rate goes down for any given submaximal intensity, and at rest! Blood vessels become more compliant and healthier. Blood volume increases via increases in plasma volume and hemoglobin content. More capillaries will grow in the working muscle to help extract more oxygen from the blood. The muscles will take up more glucose out of the blood stream, and your body will become more efficient at using fat for fuel.
Should you be afraid to start exercising? The American College of Sports Medicine recommends that if you are having symptoms of a chronic disease, you should get a medical exam before starting exercise. If you are not active, have a disease and have no symptoms, it is safe to start exercising at a light to moderate intensity as long as you have seen your physician in the last six months and gotten the “all clear” for your disease status. If you are unclear if your exercise intensity if light or moderate see the post, How to get the right heart rate for you. The risk of sudden cardiac death with exercise is low, especially if you start at a low intensity. Data from the Physician’s Health Study and the Nurses’ Health Study show that a “sudden cardiac death occurs every 1.5 million episodes of vigorous exertion in men and every 36.5 million hours of moderate to vigorous exertion in women.” (American College of Sports Medicine’s Guidelines for Exercise Testing and Prescription 11e. p14) If you do plan to see a physician first, you can use this form to help get the exercise prescription that is right for you.
The bottom line? You should not be afraid or anxious about starting an exercise program. You should be more afraid of staying sedentary! Besides, it’s fun!