EXERCISE, FITNESS, and HEALTH
In the previous document on energy expenditure, we noted that most of the population does not include intentional exercise into their daily routine, despite the many health benefits. This document will discuss the characteristics of an exercise program that promotes health and fitness. This document is based on information from chapter 13.
Fitness is defined as the ability to perform routine physical activity without undue fatigue. In order to become fit you have to apply the overload principle (1). That means when you exercise you push your body just a little bit beyond its comfort level. This forces it to adapt to the stress of exercise, improving fitness. It is true that the more you do the more you are capable of doing.
A good fitness program promotes: cardiorespiratory endurance, muscle strength and endurance and flexibility (2).
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Cardiorespiratory endurance determines how long one can continue a task. Aerobic exercise, which increases heart rate and increases the use of oxygen helps to build endurance (1). Regular aerobic exercise decreases resting heart rate, increases stroke volume which is the amount of blood pumped by the heart with each compression and increases aerobic capacity or VO2 max (2), which is the maximum amount of oxygen that can be consumed by tissue during exercise.
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Muscle strength and endurance is increased by repeatedly using muscles to move against a resisting force; this is called resistance training (1). This results in an increase in the size of muscle or muscle hypertrophy. Resistance training also helps improve bone density, because muscles are attached a bone via ligaments and when muscles are stressed during exercise, bone is also stressed in a way that promotes the uptake of calcium by the bone (2).
Flexibility is also an important part of fitness as it increases someone¡¯s range of motion.
The figure shown here documents total energy expenditure for a sedentary individual (1), and individual who exercises for 30 minutes (2) and finally an individual who exercises for 30 minutes regularly (3). What this graph shows is that exercise increases energy expenditure (4) and regular exercise increases muscle mass (5). With that comes an increase in resting energy metabolism, or basal metabolism, due to the increase in lean body mass, as shown in the pink part of the bar graph (6). Muscle is more metabolically active than adipose tissue so building muscle increases energy requirements to a greater degree. This increase in energy requirements makes it easier to maintain a healthy body weight.
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To further promote physical activity in the general population physical activity guidelines have been produced by the Canadian Society of Exercise Physiologists. The guidelines recommend that adults aged 18 to 64 engage in moderate to vigorous intensity aerobic exercise for least 150 minutes a week (1) and for stretches of at least 10 minutes or more. As well as aerobic exercise, resistance training to strengthen muscle and bone is also recommended (2). The remainder of the guide lists examples of activities that one can engage in to meet these guidelines (3).
The effectiveness of an aerobic activity is determined by measuring heart rate. The graph shown here illustrates the maximum heart rate which is a fairly linear function of age. The shaded area in orange shows the safe range for activity and it usually represents 60 to 85% of maximum heart rate. When exercising, heart rate should be in this range.
When managing strength training it¡¯s important to cover all major muscle groups. Is recommended that people repeat an exercise 8 to 12 times and that at the end of this set the muscle being exercised should be close to exhaustion. This is an example of the overload principle where you¡¯re pushing your muscle just beyond what is comfortable. This stress promotes an increase in muscle size. Increasing the weight that you lift, increases the strength of the muscle. Increasing the number of repetitions will increase endurance or the length of time that you can work the muscle before it becomes exhausted.
To fuel this exercise you need nutrients. During aerobic metabolism glucose, amino acids, and fatty acids are converted to carbon dioxide and ATP. ATP is required for muscle contraction. For example one molecule of glucose during aerobic respiration will yield about 36 molecules of ATP (1).
Anaerobic metabolism is not an efficient source of ATP because it occurs in the absence of oxygen. Glucose is converted to pyruvate and then lactate with the generation of 2 ATP molecules from one molecule of glucose (2). Despite its inefficiency, anaerobic metabolism is important during exercise.
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This figure traces the path that oxygen takes when we inhale. It¡¯s taken up from the lungs (1), enters the bloodstream, is pumped through the body by the heart (2) and reaches the muscle where it supports aerobic metabolism (3). Carbon dioxide, a by-product of aerobic metabolism, then goes into the blood (4) and is exhaled by the lungs (5).
At rest muscles do not need much energy. The heart and lungs are able to deliver enough oxygen for aerobic metabolism.
But during exercise muscles need more energy. Oxygen must be delivered to the muscles for aerobic metabolism more quickly than at rest. So breathing and heart rate go up to increase the delivery of this oxygen. When exercise first begins the breathing and heart rate is not sufficient to deliver enough oxygen to muscle.
So when you first start exercising, as shown by the red line (1), you use stored ATP and a compound called creatine phosphate which can be rapidly converted to ATP. This is shown by the red line on the graph and these compounds last about 15 seconds.
In the next phase of exercise heart rate may still not be sufficient to deliver enough oxygen for aerobic metabolism in muscles. So energy has to come from anaerobic metabolism. Glucose in the blood enters the muscle and is converted to lactate with the generation of small amounts of ATP, enough to keep the muscle going for a few minutes, as you can see that here by the yellow line (2).
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Finally, after a few minutes of exercise, heart rate and breathing should be sufficiently high that oxygen is being delivered in sufficient amounts to fuel aerobic metabolism. This stage of exercise which is shown by the blue line (3) allows for both glucose and fatty acids to be used as energy.
This figure illustrate cellular metabolism. Anaerobic metabolism which results in the end product lactic acid (2). And aerobic metabolism which converts glucose (1) and fatty acids (6) to ATP in the mitochondria (5) in the presence of oxygen (red arrow).
This figure summarizes the use of fuel in different types of exercise. At rest the preferred source of fuel for muscle is fatty acids, via aerobic metabolism (1). When you increase your activity to moderate intensity activity fatty acids and glucose are both be used to generate the energy required, via aerobic metabolism (2). When you¡¯re exercising very vigorously or at high intensity, oxygen cannot be delivered to muscle to support aerobic metabolism, so there is a shift to anaerobic metabolism and glucose as the major fuel (3).
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The many benefits of aerobic exercise on cardiorespiratory and muscle function are listed here.
Up until this point of view we have discuss exercise programs to improve the fitness of general public. I like to talk just briefly about how athletes can maximize their performance through diet, as it illustrates some important concepts of metabolism. For athletes who expend a lot of energy during competition, the goal is to maximize glycogen stores. Here we see a bar graph which clearly shows that high carbohydrate diets allow people to exercise for longer periods of time, by building by glycogen stores in the muscle. While this is not necessary for the average person trying to stay fit through moderate intensity exercise, it illustrates the importance of glucose as a source of fuel during aerobic and anaerobic metabolism.
Finally, as a required reading for this section, I like you to have a look at the section on interval training which describes some research done at McMaster University. Interval training is popular among athletes, but the McMaster research suggests that it can be applied to the general public as well. It is of interest because it can provide the benefits of conventional exercise programs, in less time. Be sure that you can answer the questions on the slide.
Pg 601 (3e)
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This wraps up our discussion of exercise. Be sure to do the self- assessment questions to help review this topic before moving on to the study review on gaining muscle and losing fat.
6. What shift in fuel use occurs when changing from moderate to high-intensity exercise?
a) There is a shift from using glucose only, during moderate exercise, to using both glucose and fatty acids. This
is because, during vigorous exercise, oxygen cannot be delivered to muscle fast enough to support the
oxidation of glucose.
b) There is a shift from using fatty acids only, during moderate exercise, to using only glucose. This is because,
during vigorous exercise, oxygen cannot be delivered to muscle fast enough to support the beta-oxidation of
fatty acids.
c) There is a shift from using glucose and fatty acids, during moderate exercise, to using only glucose. This is
because, during vigorous exercise, oxygen cannot be delivered to muscle fast enough to support the beta- oxidation of fatty acids.
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Is simultaneously gaining muscle and losing fat possible?
In traditional bodybuilding circles and in nutrition/exercise research, gaining muscle and losing body fat have been considered mutually exclusive.
This is because losing fat requires a hypocaloric diet, while a hyperenergetic diet is seen as necessary to gain lean body mass without the assistance of performance enhancing drugs.
This presents a problem for people who want to gain muscle and lose body fat at the same time and not sacrifice one for the other.
But in 2016, a group out of McMaster University challenged this idea with a well controlled study where they took 40 participants and divided them into a high protein group and a control group with all diets provided over 4 weeks.
Diets corresponded to an individually constructed energy-restricted meal plan with was approximately 40% below their energy needs for weight maintenance.
The high protein group (PRO) received 2.4g/kg/day of protein, while the low protein group (CON) received half the amount, at 1.2g/kg/day. Participants were placed on a 3-d rotating diet with lunchtime and dinnertime meals provided as prepackaged frozen meals (Copper County Foods). Both groups received beverages containing whey protein to be consumed throughout the day, with one beverage being consumed immediately after training in the presence of the investigators on exercise days.
Taking a closer look at the diet composition, we can see that compared to the CON group, the PRO group had significantly greater intake when expressed in absolute and relative values.
Their intake in both groups was similar and not statistically different. As you¡¯ll see shortly, this is an important point as carbohydrates provide fuel for the type of exercise these participants performed.
Since caloric intake wasn¡¯t different between the groups, the PRO group ingested significantly less kilocalories from
as compared to the CON.
Though diet is an essential component of body composition, the type of exercise we do will have a big impact on our composition as well.
Participants reported to the laboratory 6 days/week for supervised exercise training that consisted of a full-body resistance exercise circuit twice per week, high-intensity interval training (HIT) twice a week doing intervals of cycle ergometer sprints, a weekly time trial on a cycle ergometer, and a plyometric body weight circuit.
During non-exercise times, participants had to complete 10,000 steps per day, and in fact, step counts for the participants averaged over 11,000 steps per day.
After 4 weeks of this protocol, both groups lost the same amount of weight (BM), which isn¡¯t surprising given that caloric deficit wasn¡¯t different between the groups.
We can see that the PRO group had a significantly greater increase in lean body mass (LBM) while also having a greater decrease in fat mass (FM).
Though the scale may show the same weight loss, the body composition change between groups was different, showing that the foods that we eat matter as well as the calories we ingest.
This study tells us that a higher protein-containing diet consumed during a period of energy deficit with high-intensity exercise resulted in an increase of lean body mass and a greater decrease in body fat when compared to an energy deficit with lower protein.
Some important points to note are that this study was performed in healthy young males only. This was also done under strict laboratory conditions with food being carefully measured and provided.
Another consideration is that since fat content was decreased in the PRO group, it cannot be concluded that protein was exclusively responsible for the effects alone, however physiology research tells us that fat likely would not have a major impact here outside of the caloric contributions.
This wraps up our look at this study.
As a self-reflective activity, try to think about how many carbohydrates, fats, protein, and total calories you¡¯d ingest if you were part of the PRO and CHO groups.
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