Physiological responses to chronic exercise

As we’ve seen in the previous video, one single episode of physical activity causes major but transient changes in the physiology of the body organs. To make sure long lasting, health specific changes in physiology occur, we have to repeat activity over and over. That is, we need to train. One of the most amazing things about our bodies is their ability to change shape, size, and functional capacity in response to repeated physical activity. That is, in response to chronic exercise. This will be the focus of this video. While the most astounding changes occur in elite athletes, who train incredibly hard, we will confine our examination of training affects to a more moderate level of regular exercise, achievable by the rest of us.

The long term effects of regular exercise depend on the type of exercise undertaken. In the case of aerobic exercise, regular training builds fitness. In scientific terms, it increases aerobic capacity. The VO2 max is an assessment of the maximum amount of oxygen you can use, and therefore the amount of physical work you can perform. Having a high VO2 max is a prerequisite for elite athletic performance, but from a clinical point of view, aerobic capacity is also extremely important. Many patients undergo a stress test on a treadmill, with the purpose of assessing the patient’s aerobic capacity, and thus ability to exert themselves. In order to increase fitness, we need to push the cardiovascular, respiratory, and musculoskeletal systems to work harder.

This is the only way in which they will adapt to become more efficient and therefore increase an individual’s fitness. We have seen that exercise causes an increase in cardiac output by increasing the heart rate, that is, the number of times the heart beats per minute, and the stroke volume, that is the volume of blood ejected from the heart each time it beats. The heart has an incredible ability to remodel itself as a result of regular exercise. In very fit people, the heart becomes so efficient that the resting heart rate can decrease very significantly, while the resting stroke volume increases. That is, the heart has to beat fewer times per minute in order to drive a normal cardiac output.

This is as a result of changes in the size and the volume of the heart’s chambers. While such changes may be much more modest with lower intensity training, heart health in the long term is improved and regular exercise reduces the risk of cardiac disease. Regular exercise reduces the long term risk of hypertension, but it will decrease blood pressure only modestly in those with normal blood pressure. However, the effects of exercise training on blood pressure are much more marked in those with existing hypertension. This is because of the wide ranging neural, hormonal, biochemical changes that occur as a result of regular exercise, resulting in healthier blood vessels and better managed fluid balance within the body.

Ventilation, or lung function, normally is not a limiting factor for exercise performance in healthy, untrained people, and as such, the respiratory responses to regular exercise contribute less to increased fitness than do changes in the cardiovascular and muscular systems. In the muscles, regular training results in the growth of new blood vessels, allowing greater capacity for blood flow and thus increased capacity for activity. Regular exercise also causes metabolic adaptations in muscles that allow the tissue to use oxygen more efficiently and to increase the ability to use fat as a fuel source, and to buffer increases in lactic acid production more efficiently.

As such, regular aerobic exercise can aid in weight management and prevention of diabetes, due to metabolic adaptations, in addition to the actual calories burned during exercise. Resistance exercise, such as lifting weights, will result in increased strength over time, due to increased growth in muscle. This is known as muscle hypertrophy. Simply put, strength is directly related to muscle size. Therefore, regular, progressive training results in increased strength. The weight used and the number of repetitions is key to determining the changes in muscle strength. Hence, to continue to develop strength, progressive training is key. Resistance exercise also helps to strengthen bones and joints.

There are also long term benefits to be had, particularly in musculoskeletal health, from engaging in exercise that specifically develops flexibility, such as yoga. The responses of the body to long term exercise will vary across population, due to individual genetic differences, and also differences in the type, intensity, and duration of exercise. Unfortunately, when training ceases, a so-called de-training effect can be seen. Many of the beneficial effects of exercise training, from both aerobic and resistance activities, diminish within a matter of weeks if physical activity is substantially reduced. And effects disappear within a matter of months if physical activity is not resumed. The phrase “use it or lose it” is particularly apt when it comes to exercise. However, it’s not all bad news.

Exercise at any stage of life is beneficial. A history of physical activity, especially in childhood and young adulthood, is protective against a range of non-communicable diseases, as will be explored throughout the rest of this course.