The increase in the prevalence of obesity has seemed to lead to an increase in the trend of healthy eating and exercise over the years (Flegal, Carroll, Ogden & Johnson, 2002). Interestingly, exercise is actually considered a form of stress, as it is a “disruption of homoeostasis” (Plowman & Smith, 2011, p.22). Exercise is defined as “a single acute bout of bodily exertion or muscular activity that requires an expenditure of energy above resting level and that in most, but not all, cases results in voluntary movement” (Plowman & Smith, 2011, p.705). When we run our heart rate rises, our muscles move faster, our respiratory rate increase, and so on. When we lift weights our muscles are pushed to work harder either via repetition and sets or the amount we lift. During these time periods, our body is struggling to maintain homoeostasis; a healthy form of stress that can make the human body more efficient and productive.
Exercise will affect each system differently and different exercise will affect the different systems differently. It is said that “health-related physical fitness is composed of components representing cardiovascular-respiratory endurance, metabolism and muscular fitness” (Plowman & Smith, 2011, p.22). In other words, the main systems that are affected by exercise are our cardiovascular, respiratory, and muscular systems. Exercise also affects our metabolism, which is not a system on its own; however is a key component to provided energy for our body.
When we exercise, we need energy. Therefore energy production, or metabolism, is affected by exercise. Metabolism is defined as the “the total of all energy transformations that occur in the body” (Plowman & Smith, 2011, p. 27). To make adenosine tripohophate (ATP), the body’s form of energy, from the food we consume we use a process called cellular respiration. Our resources included carbohydrates, triglycerides and amino acids. Through carbohydrate metabolism, we are able to break down carbohydrates into glucose or glycogen. From there our glucose or glycogen will go through the process of glycolysis to make pyruvate or lactic acid. The acids then become acetyl coenzyme A, which would then go through the Kreb cycle and the electron transport system to create ATP. From our carbohydrate we get a range of thirty to thirty-three ATPs; depending on the muscle group and if glucose on glycogen was used. With triglycerides, we must break it down into fatty acids and glycerol. The fatty acids then go through the process of beta oxidation to create acetyl coenzyme A. The number of ATP formed depends on the number of carbon pairs found in the triglyceride. Amino acids make about ten to fifteen percent of our energy supply; and therefore are used as a last resort (Plowman & Smith, 2011).
During exercise, the goal of metabolism is to do three things. First, increase mobilisation and usage of the free fatty acids in adipose tissue and intramuscular stores. Second, decrease the amount of glucose sent to muscles that are not being used while still sending some to our nervous system; particularly our brain. Third, increase the breakdown of glucose stores in the liver and muscles. This creates glucose from non-carbohydrate sources (Plowman & Smith, 2011).
We used a different source of energy depending on the type of exercise. If the duration of the exercise were to decrease and or if there is an increase in intensity then carbohydrates would become our main source. However, if we increased our duration and decreased our intensity the many sources would be triglycerides. When the duration is longer than an hour that is when amino acids make a small contribution to the energy production. The effects of exercise on our metabolism, in turn, affect the efficiency of other systems in the body, such as the respiratory system.
While exercising, one of the first things we mentally note is a change in is our Respiratory System. This is quite simply because of the high demand for energy, exercise creates. Our respiratory system is used to provided energy via aerobic metabolism, in other words, it brings in the oxygen we need to create ATP. Therefore, it makes sense that we breathe more frequently to help our body get the energy it needs. To speed up the process, it would be best if the rate at which oxygen disassociated from haemoglobin increased. This is exactly what happens. Here is how: as we create more energy the waste product, carbon dioxide, also increases. Therefore our partial pressure of carbon dioxide increase; and because of the carbonic acid-bicarbonate buffer system, there is also a decrease in the pH levels (Martini, Ober & Nath, 2012). There is also an increase in body temperatures, which is a byproduct of energy production. These conditions increase the rate of dissociation of oxygen from the protein haemoglobin.
What is interesting is our misconception with the idea of our respiratory system as a limiting factor. The phrase, “I am out of breath”, is commonly heard by runners and gym goers. However, our level of respiratory activity is almost equal to the rate of work being done. If we take our increased activity into hand and our respiratory system’s large reserve, we find that the respiratory system does not limit our ability to exercise in any way (Plowman & Smith, 2011, p.385).
We do not see many adaptions in the respiratory system as a result of training. As a stressor, exercise does not stress the limitations of the respiratory system; and as a result, we do not see any long or short term changes. There are some changes in the respiratory system as a result of water based exercises. We find that they have a higher lung volume and capacities. The reason for this is unknown. However, there is a theory that “swimmeraˆ¦breath against the resistance of water, using a restricted breathing pattern with repeated expansion of the lungs to total capacity” (Plowman & Smith, 2011, p.305). Swimmers also do work in the horizontal position; a position “optimal for perfusion of the lung and diffusion of respiratory gases” (Plowman & Smith, 2011, p.307). In swimmers, we also find that there is a report of higher diffusion capacity. This is also seen in runners. However, this is more likely due to circulatory changes.
A slight increase in our minute ventilation is also seen as a result of training adaptation. Minute ventilation or minute volume is defined as the amount of air coming into and leaving the respiratory system per minute (Martini, Ober & Nath, 2012). It is the components of minute volume that we see the change in, which affects the minute volume. Minute volume equals to how many breaths we take per minute times our tidal volume. Our tidal volume is the “amount of air you move into or out of your lungs during a single respiratory cycle under resting conditions”; in other words, it is quite breathing (Martini, Ober & Nath, 2012, p. 739). With exercise, our tidal volume adapts and increases at rest. Therefore, individual who frequently exercise will develop a large tidal volume. As a result, the minute volume is higher after training than before, allowing for the ability to increase our endurance (Plowman & Smith, 2011).
Besides these changes, we do not see a lot of long-term adaptations in the respiratory system as a result of exercise. The changes mentioned are also very minimal. An area we see a lot changes in response to exercise is our cardiovascular system and muscular system. “The ability to deliver oxygen (and other substances) depends on the proper functioning of the cardiovascular system” (Plowman & Smith, 2011, p.323). As we exercise the need for oxygen increases and carbon dioxide concentration in our blood increase. Chemoreceptor and baroreceptors detect this change in the blood. To get the proper resources to the proper place certain factors of our cardiovascular system start to increase during exercise. These factors include our stroke volume, heart rate, cardiac output, and systolic blood pressure. Stroke volume is the amount of blood that is ejected from the heart after every beat; the amount per minute is the cardiac output. Systolic blood pressure is the blood pressure during a contraction (Plowman & Smith, 2011). The kind of exercise will affect how much these factors will increase or how rapidly it will increase. For example, during the short term, light to moderate aerobic exercise make our factors increase rapidly. However, during incremental exercise, our factors will “increase in a rectilinear fashion” as the workload increases.
Our vascular system also plays an important role as we exercise. When exercising we find that there is a decrease in resistance of the arteries and veins, in other words, we see an increase in vasodilatation. This allows for more blood to go to working muscle, while making sure the blood pressure does not rise excessively (Plowman & Smith, 2011). Our cardiovascular system will also contribute to maintaining homoeostasis of our body temperatures.
When it comes to thermoregulation the environment surrounding our bodies can be very influential. However, our body is able to maintain an internal temperature via metabolic heat production, body heat radiation, conduction, convection and evaporation. Our cardiovascular system plays a role by capturing the heat exerted by our muscular system and sending them to be released via our peripheral vascular system. One of our primary defences against heat stress, especially while exercising, is sweating. However, there are situations where the thermoregulatory and metabolic demands are not meet by the cardiovascular systems. In this case, an individual can develop heat illness such as heat exhaustion and heatstroke. That is why it is important for those who exercise to keep hydrated before, during and after exercise (Plowman & Smith, 2011).
Over time we will find that exercise will cause our cardiovascular system to adapt. With endurance training, we will see an increase in blood volume and plasma volume. However, the increase in plasma volume will be seen at the beginning of the training while blood volume increase will not happen until much later. As a result of endurance training, individuals develop a lower heart rate at rest as well as the maximal oxygen consumption (Plowman & Smith, 2011).
Approximately forty percent of the deaths in America are caused by cardiovascular disease. One of the top cardiovascular diseases is coronary heart disease. However, there are studies that show exercise can reduce the risk of coronary heart disease. Exercise can even reduce the risk of factors that cause cardiovascular diseases; such as properties of metabolic syndrome. Metabolic syndrome is characterised by high visceral abdominal obesity, dyslipidemia, reduced glucose tolerance, insulin resistance, and hypertension. Together, these are factors that can cause cardiovascular diseases. By exercising, we can reduce the risk of many diseases, not just one (Plowman & Smith, 2011).
The second system that is largely affected by exercise is our skeletal muscular system. Generally, our skeletal muscles are important for posture, heat generation, and motion. To help perform these actions our nervous system plays the control our skeletal muscles. A motor unit is the combinations of the motor neurone and the muscle fibres it stimulates. ATP plays an important role here. This is because one neurone gives the signal for the muscle fibres to contract; the muscle fibres will need the energy to contract and then relax?? (Plowman & Smith, 2011).
Human muscle fibres are categorised by contractile properties and metabolic properties. From the contractile perspective, we have fast-twitch fibres and slow-twitch fibres. The ability for the fibre to contract slowly or quickly has more to do with the motor neurone then the fibre. Alpha-1 motor neurones are larger, have high recruitment threshold, and faster conductivity velocity; innervate fast twitch fibres. Alpha 2 motor neurones are smaller, have slower conduction velocity and low recruitment threshold; innervate slow twitch fibres. Metabolically, fast twitch fibres can make energy via oxidation and glycolytic metabolism or just glycolytic metabolism. However, slow twitch fibres can only make energy via oxidative metabolism (Plowman & Smith, 2011).
Through studies, we have found that athletes that practice endurance activities will have a higher percentage of slow twitch fibres. Individuals who are involved in resistance activities will have a higher percentage of fast twitch fibres. However, it is believed that this is more genetically based, then based on nurture. That is to say, that it is easier for some who has a high amount of fast twitch fibres will be better at resistance activities. While those with high slow twitch fibres are better at endurance activities. Therefore, the contractile properties of muscle fibres cannot be changed via exercise; however, our metabolic properties can be. It is possible for training to cause enough fast twitch fibres to change metabolically, so that they switch from oxidative-glycolytic metabolism to glycolytic metabolism (Plowman & Smith, 2011).
While training and exercising, we must be aware of muscular fatigue and muscular soreness. Muscular fatigue results from a loss of muscle functions and is largely depend upon the type of muscle fibre being used. Different exercises will use different muscle fibres; therefore, different kinds of exercise will cause muscle fatigue differently. For example, in static activity hydrogen ions increase, glycolysis is inhibited, fewer calcium ions are released in the sarcoplasmic reticulum and there is an occlusion of blood flow. Any of these, if enough or a combination of all of them, can cause muscle fatigue. Muscle soreness is the same idea as “overexertion” (Plowman & Smith, 2011, p. 547). There are two types: immediate-onset soreness and delayed-onset muscle soreness. Immediate-onset soreness is pain that occurs during and immediately after exercise. When over exercising hydrogen ion concentration and lactic acid levels increase, this increase causes an over stimulation of pain receptors. It is believed that this is what cause immediate-onset soreness. However, it is not sure what causes delayed-onset muscle soreness (DOMS). DOMS is the pain that is felt at least eight hours after exercising and, reaches peaks and falls over the next ninety-six hours. Athletes and trainers must beware to avoid these conditions because it can affect athletic participation and performance (Plowman & Smith, 2011).
Different exercises lead to muscle fatigue differently than another type of exercise. This is the same as the adaptations seen in our muscular system. Different kinds of exercises will lead to different adaptations. “Resistance training is used to improve overall health, improve athletic performance; rehabilitate injuries, and change physical appearance” (Plowman & Smith, 2011, p. 580). Muscular adaption’s, however, also rely heavily on their individual goals; and occur at different rates. Trainers must remember to apply a training program based on the individual or team and their capabilities (Plowman & Smith, 2011).
Metabolism, cardiovascular system, and the muscular system are the main aspects of our body that are affected by exercise. However, our other systems are also affected. Our skeletal system is important for protection, support, mineral storage, hematopoiesis and movement. Studies have shown that exercise has a positive effect on bone health and helps avoid disease such as osteoporosis. Physical activity creates an increase in mechanical force that leads to mechanotransduction. Mechanotransduction is the process of osteocytes modelling and remodelling the bones. This makes the bone stronger. Bending our bones also causes stress (compressive and tensile stress) that changes the hydrostatic pressure of our bones. The change in pressure increases the movement of the fluid within the bone. Fluid in the bone carries the nutrients and wastes; as well as results in the formation of new bone. Exercise helps the body to reach peak bone mass while still growing, offset menopause and slow down bone loss that occurs later in life. However, if exercise is done excessively their “activity can exceed the adaptive ability of bone, resulting is overuse injury” (Plowman & Smith, 2011, p. 501).
The nervous system was seen coming into play with our muscular system; however, our nervous system also works with our endocrine system when responding to exercise. When responding to stress in general, our nervous system and the endocrine systems will come into play. Since exercise is a stress, we see a response from the nervous system and the endocrine system. Specifically, the sympathetic and the parasympathetic come into play during different points of the exercise. The sympathetic nervous system (SNS), our fight or flight response, will come into play during exercise. While our parasympathetic nervous system (PNS), rest and digest, will be important for recovery; breaking down energy for our muscle recovery, taking deep slow breaths, and so on. The SNS will, during exercise, ensure to enhance our cardiovascular functions, regulate blood flow and maintain blood pressure and thermal balance, and increase fuel mobilisation (Plowman & Smith, 2011. It has also been found that after long bouts of exercise a group of neuropeptides called endogenous opioids is released in the central nervous system. Endogenous opioids, or opioids, are a famously know as opium from the best and for subsiding pain (Jonsdottir, 2002). While running as pain levels reach certain levels opioids are released, and are also known to cause “runners second the wind” or “runners high” (Widmaier, Raff & Strang, 2008, p. 171).
The endocrine system also plays a role when exercising. While exercising there is an increase in the release of our metabolic hormones; glucagon, insulin, growth hormone, epinephrine and norepinephrine. These hormones work together to maintain blood glucose levels and mobilise fuel for ATP production. Epinephrine and norepinephrine also help to enhance cardiac function and maintain fluid and electrolyte balance. Adaptive, our endocrine system may change due to exercise. However, it depends on the individual. The adaptation could make the individual “more sensitive to lower levels of hormone so that the same effect occurs following training even without a changing baseline” (Plowman & Smith, 2011, p. 645).
Our immune system will also respond to exercise. It has been found that will moderate exercise will lead to higher numbers and activity of neutrophils, natural killer cells, B and T cells, macrophages, and more. Thus making out immune system stronger. However, during excessive exercise, we see a decrease in natural killer cells, lymphocytes and neutrophils. It is believed that this is likely for the vulnerability to acute infections.
“No pain, no gain”, is what is often said among friends when exercising. It is important to remember that exercise is a stressor, and that one will feel pain as a result. It is also important to beware of the effects of over-exercising. Exercise, if done right, can help avoid, delay and lessen the effects of disease; as well enhance our bodies to function to its’ prime.