We have described how the increased metabolic activity of the muscles during exercise drives the cardiovascular response to exercise. This is exactly the same reason why ventilation increases during exercise. Because our oxygen demands have increased, delivery of oxygen to the tissues and removal of excess carbon dioxide also needs to increase. This means we need to move more air into and out of the lungs. That is, our breathing rate needs to go up. We also need to deliver more blood to the lungs to pick up oxygen and to deliver carbon dioxide. The cardiac output to the lungs therefore also increases with exercise.
Under normal resting conditions, we inhale and exhale about half a litre of air with every breath and in total about six litres every minute. In order to fuel increased metabolism with exercise, this respiration rate needs to increase. Again, depending on the intensity of exercise– low, moderate, or strenuous– ventilation rate and depth will change several-fold, perhaps up to 30-fold, in elite athletes during strenuous exercise. The increased oxygen consumption with exercise is driven by this coordinated increase in cardiovascular, muscular, and respiratory activity. The maximum amount of oxygen that you can use is termed the VO2 max and is a measure of aerobic fitness. VO2 max responds very well to repeated exercise bouts.
And this is something that will be explored in the next video. What other immediate changes do we see in the body in response to exercise? The brain coordinates and regulates many of the activities related to exercise. But it also responds to exercise, resulting in increased feelings of alertness and focus and, ultimately, fatigue if exercise is prolonged. The release of endorphins, characterised as the runner’s high, is well documented. But other hormones and neurotransmitters are also released during and after exercise, including serotonin. This may contribute to the long-term effects of exercise on brain health that will be explored in a later video. Peripherally-acting hormones, such as adrenaline, are released during exercise.
This helps to drive the increase in cardiac output that we have described. Hormones released during exercise regulate which fuels are used to drive cellular metabolism. This has implications for long-term health that, again, we will explore later in this course. Overall, the responses to exercise are regulated by the nervous system and the hormonal system, both in the short-term and, as we will see, in the long-term. We have focused thus far on the consumption of oxygen with exercise– so-called aerobic exercise– such as brisk walking, jogging, or cycling. In an exercise plan, aerobic exercise is generally carried out at moderate intensity for long periods of time and involves large muscle groups.
But what about the other broad category of exercise, anaerobic exercise, such as short bursts of high intensity effort, like sprinting, or resistance exercise, such as weightlifting? Because metabolic demands increase because of the effort required, for example, to lift a heavy weight, cardiac output and ventilation also increase. But not to the same extent as with aerobic exercise. We will also see increases in heat production that require thermal regulatory responses. Thus, some of the short-term responses to a single bout of resistance or anaerobic exercise are similar to that of aerobic exercise, but of differing magnitude. In the next video, we will look at the longer term changes that occur in the body in response to repeated bouts of anaerobic or resistance exercise.
Many people who exercise do so outside of the gym by playing individual or team sports. These sports can involve a combination of aerobic and anaerobic or resistance training coupled with training in agility, balance, and sports-specific skills. This may involve a combination of running while hitting, throwing, or kicking a ball. Still others engage in activities such as dancing, yoga, or Pilates, which again, build muscle strength and aerobic fitness over time, albeit to different degrees. What all types of physical activity have in common is the changes that they bring about in the function of our organ systems. From a health perspective, it is the repeated occurrence of these changes over time that can prevent or help to treat different diseases.
We will explore the physiology underlying these changes in the next video.