Introduction
Fred Hatfield, Ph.D., MSS & Dan Gastelu, MS
As we have uncovered 无遮盖的 in the introduction, we have a tremendous 巨大的 influence
on shaping the health and fitness attitudes and practices of those around us like friends,
family members, co-workers and clients. Your ability as fitness professionals to educate and
effectively draw your clients into the fitness lifestyle and optimal 最佳的 health comes from a
plan that is based in the knowledge of muscular, cardiopulmonary 心肺的 and metabolic
adaptations 代谢适应. These adaptations are known as the training effect. The “training
effect” is your body’s adaptation to the learned and expected stress imposed 施加影响 by
physical activity. Your bodies begin to change at the cellular 细胞的 level, allowing more
energy to be released 释放 with less oxygen. Your heart and capillaries become stronger and
more dispersed 被分散的 in order to allow a more efficient flow of oxygen and nutrients. Your
muscles, tendons 腱 and bones involved with this activity also strengthen 变 坚 固 to
accommodate 适应 a better proficiency 熟练 at performing this activity. In time your body
releases unnecessary fat from its frame and your stride and gait 步法 become more efficient.
Your resting heat rate and blood pressure drop. These adaptations can be achieved through
an educated trainer who can develop an appropriate 适当的 fitness and health plan. While
these muscular, cardiopulmonary and metabolic adaptations are indeed 的确 important we
must understand that these positive adaptations would not be possible without sufficient 充
分的 energy to bring about this training effect. Therefore we must begin by learning about
where this energy comes from.
Training effect: An increase in functional capacity of muscles and other bodily 身体的 tissues
as a result of increased stress (overload 超载) placed upon 在...之上 them.
Where Does Energy Come From?
All energy on earth comes from the sun. Plants use the light energy from the sun to form
carbohydrates 碳水化合物, fats and proteins. Carbohydrates are sugars and starches 淀粉
used by the body as fuel 燃料 molecules 分子 and to store energy. Fats are compounds 化合
物 that store energy. Proteins are important components 成分 of cells and tissues and are
large complex 复(合)体 molecules composed 组成 of amino acids. (We will discuss
carbohydrates, fats and proteins in more detail in Section 5 of this text.) Humans and other
animals then eat plants and other animals to obtain energy required to maintain cellular 细
胞的 activities. The body uses carbohydrates, fats and proteins consumed 消耗 daily to
provide the necessary energy to maintain cellular activity both at rest and during activity.
Since all cells require energy, your bodies must have a way to convert 转换 carbohydrates,
fats and protein into a biologically 生物学, 生态学 usable form 形状 of energy to fuel physical
activity. The ability to run, jump and lift weights is contingent 偶然发生的 on and limited by
your ability to transform 转化 food into biological 生物学的 energy. These physical abilities are
contingent on thousands of chemical reactions 反应 that occur throughout our bodies all day
long. Collectively 聚合性地 these reactions are known as metabolism. These many chemical
reactions occurring in our bodies must be regulated 调整 to maintain a balance. The body
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consists 存在于 of trillions 大量 of cells, which are organized into tissues, organs, and systems.
We will discuss this intricate 复杂的 organized system in more detail in Unit 2. The body’s
components work together in a highly organized manner 方式 to maintain a balance.
Metabolic activities are continually 不断地, 频繁地 occurring in the trillions of cells in your
body and must be carefully regulated to maintain a constant 不变的 internal environment, or
steady 稳定的 state 状态. This steady state must be maintained regardless 不管, 不注意, 不
顾 of your ever-changing external environment. This automatic tendency 趋向, 倾向 to
maintain a relatively constant internal environment is called homeostasis. 体内平衡, 内环
境稳定
Homeostasis: The automatic tendency to maintain a relatively constant internal
environment
Homeostasis
Walter Bradford Cannon is credited 相信 with coining 创造 the term homeostasis to refer 归
诸于 to the processes that maintain a constant internal body environment. For homeostasis
to work, there must be feedback 反馈, 反应 systems that various 不同的, 各种的 physiological
生理机能的 functions turn off and on. Imagine a feedback system like the thermostat 自动调
温器 in your furnace 火炉 or air conditioning system. If the temperature increases above the
set point determined by the system, then the thermostat shuts off the furnace. In this way
the temperature is kept at a desired steady state. If the temperature decreases below the set
point determined by the system, then the thermostat turns on the furnace to maintain a
desired steady state. A feedback system revolves 循环出现 around a cycle of events.
Information about a change is fed back to the system so that the regulator 调整器(in this
example the thermostat) can control the process (in the above example of temperature
regulation). A good example of homeostasis in the body is the method by which the body
maintains a constant temperature of 98.6 degrees Fahrenheit 华氏温度计. If physical exertion
劳力, 用力 or external heat causes the body temperature to rise, the brain sends a signal 信
号 to increase the rate of sweating 出汗. Heat is carried away 使失去自制力 in the evaporating
蒸发用的, 蒸发作用的 sweat. If body temperature begins to drop due to a cold external
environment, shivering 发抖 begins to generate 导致 heat and keep the body temperature at
that critical 98.6 degrees F. Other metabolic functions under homeostatic control include:
• Hormone 荷尔蒙 production and concentration level maintenance.
• Maintenance of serum 血清; 浆液 oxygen levels and carbon dioxide 二氧化碳 levels.
• pH balance in the blood and cells.
• Water content 含量 of cells and blood.
• Blood glucose 葡萄糖 levels, and other nutrient levels in the cell.
• Metabolic rate.
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The concept of homeostasis is of special interest to the fitness enthusiast 爱好者. You are in
equilibrium 平衡 with the environmental stimuli 剌激 imposed upon you. Think for example,
how your muscles change in response to different training programs. If you spend most of
your time lifting heavy weights, your muscles will grow larger. A shift in your homeostasis has
taken place 发生. The simple action of weight lifting causes more protein synthesis 合成 in the
muscles being exercised with weights. Hormone levels change to accommodate this growth.
On the other hand, if you choose to run several miles per day, your muscles will take a
different form: develop a higher endurance capacity, stimulate 兴奋, 刺激 the formation 形
成, 结构 of more fat burning slow twitch 抽搐 muscle fibers, and develop a higher capacity to
use oxygen in energy production. Nutrient intake 摄取量 is an important factor, which can
affect your homeostatic balance as well. Eating too much of the wrong foods, or too little of
the right foods can cause homeostasis to shift. Too much fat and calories, and your body
stores fat. Not enough protein, and your muscles break down 分解. Not enough
carbohydrates, and you will feel tired sooner. For optimum 最适宜的 homeostasis and
metabolism, eating the right nutrients in the right amounts at the right times is vital 重要的.
Metabolism
In order to build biomolecules 活质分子 and sustain 持续 life, the body needs energy. The
body gets its energy from the breakdown of nutrients like glucose, amino acids 氨基酸 and
fatty acids 脂肪酸, To construct molecules 分子构造 there must be molecular destruction 破坏
going on simultaneously 同时发生,同时存在 to provide the energy required to drive these
biochemical 生物化学的 reactions.
The many biochemical processes that make up 弥补 the body’s metabolism are categorized
into two general phases; anabolism 组成代谢 and catabolism 分解代谢. From the start, it
must be understood that anabolism and catabolism occur simultaneously all the time.
However, they differ in magnitude 巨大, 重大,depending on the level of activity or rest and on
when the last meal was eaten. When anabolism exceeds 超过 catabolism, net growth occurs.
When catabolism exceeds anabolism, the body has a net loss of substances 物质 and body
tissues and may lose weight.
Anabolism includes the chemical reactions that combine (使)结合 different biomolecules to
create larger more complex ones. The net result of anabolism is that new cellular material is
made, such as enzymes 酶, proteins, cell membranes 膜, new cells, and growth of the many
tissues. That energy is stored in the form of glycogen 糖原 and/or fat, and in muscle tissue.
Anabolism is necessary for growth, maintenance, and repair of tissues.
Catabolism is the term 范围 used to describe the chemical reactions that break down complex
biomolecules into simpler ones for energy production, to recycling 再循环 of molecular
components, or for their excretion 排泄, 分泌. Catabolism provides the energy needed for
transmitting the nerve 神经 impulses 冲动, 搏动 and muscle contraction 收缩.
Metabolism includes only the chemical changes that occur within tissue cells in the body. It
does not include those changes to substances that take place in the digestion 消化 of foods in
the gastrointestinal 胃肠的 system. A healthy metabolism needs many nutrients to function
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optimally. A slight 轻微的 deficiency 缺乏, 不足 of even one vitamin can slow down
metabolism and cause chaos 混乱, 混沌 throughout the body. The body builds thousands of
enzymes to drive your metabolism in the direction influenced by activity and nutrition. So,
when you are training several hours a day, you better make sure that your diet contains the
nutrients it needs to feed the many metabolic pathways.
Metabolism: The chemical processes occurring within a living cell or organism 生物[体] that
are necessary for the maintenance of life. In metabolism some substances are broken down
to yield 出产, 给予 energy for vital processes while other substances, necessary for life, are
synthesized 合成.
Anabolism: The building up in the body of complex chemical compounds from simpler
compounds (e.g., proteins from amino acids).
Catabolism: The breaking down in the body of complex chemical compounds into simpler
ones (e.g., amino acids to individual proteins).
Your Metabolic Set Point 调整点
From the discussion of homeostasis and metabolism above, you can see that the body is a
tightly 紧紧地, 坚固地 run collection of many biochemical reactions. During the intensive
加强的 study of weight loss, it was discovered that your body seeks 寻求 to maintain a
certain base rate of metabolism, which has come to be called your metabolic set point
(which results in your basal metabolic rate). This set point is controlled by your genetics
遗传学 and the environmental factors. Researchers have demonstrated that you can change
your metabolic set point through dietary 规定食物 means 方法, 手段 and physical activity.
The metabolic set point is the average rate at which your metabolism runs, and will result in
a body composition set point. People with a slow metabolism seem 象是, 似乎 to store fat
easily, while people with a fast metabolism seem to be able to eat and never get fat. Your
metabolic set point can be influenced by the external environment (climate 气候), nutrition,
exercise, and other factors. Studies have demonstrated that when individuals go on a low
calorie diet, the body’s metabolic set point becomes lower to conserve 保存, 使(能量等)守恒
energy. It actually resets 重新设定 itself to burn fewer calories, thereby 因此 conserving
energy. Exercise tends to keep the metabolic rate up, and more aerobic exercise tends to
cause the body to burn more fat for energy.
Metabolic set point: The base rate of metabolism that your body seeks to maintain; results
in your basal metabolic rate.
Basal metabolic rate: The minimum energy required to maintain the body’s life function at
rest. Usually expressed in calories per hour per square meter of the body surface.
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Food and Metabolism
The type of food eaten can also influence your metabolism. The food you eat can either be
burned to liberate energy, converted into body weight, or it can be excreted. All foods release
heat when they are burned. This release of heat is measured in kilocalories 千卡, 大卡. A
calorie 卡路里 is a unit of heat. Practically 事实上 speaking this unit is too small to be useful
therefore 因此, 所以 the kilocalorie is the preferred 首选的 unit in metabolite studies. Not all
foods are burned completely to produce energy. Some of them are only partially 部分地
degraded 退化的 to provide building blocks 阻滞, 阻塞 to support repair and growth. Generally
通常 speaking, the calories coming from protein are used for maintenance, repair, and growth
of new tissues and organs 器官. Calories from carbohydrates are used for energy. Calories
from conventional 惯例的, 常规的 sources of fat are prone 有...倾向的 to be stored as fat
since they already have the same molecular structure as body fat. The heat liberated 解放的
from a particular food is thus a measure not only of its energy content but also of its tendency
to be burned as heat. This is known as the thermogenic 生热的, 产热的 effect.
Kilocalories: The amount of energy released when food is digested.
Calorie: A unit of heat.
Thermogenic effect: The heat liberated from a particular food is thus a measure not only of
its energy content but also of its tendency to be burned as heat.
Increased thermogenesis means increased heat production, which correlates 相关, 联系 with
increased oxygen consumption 消耗, and an increased metabolic rate. The more heat your
body produces, the more oxygen it needs, because heat cannot be liberated in the absence
缺乏 of oxygen 氧. Food efficiency 效能 is simply a measure of how efficiently a particular
food is converted to body weight. Foods with high food efficiency are prone to be converted
to body weight while foods with low food efficiency are prone to be burned as energy.
Understanding how your body will use the calories you consume can help you in setting up
your nutritional program. Simply counting calories will not lead to body fat loss. The heat
liberated from a particular food, whether it is fat, protein, or carbohydrate, is determined by
its particular molecular structure, and this structure determines 决定 its thermogenic effect.
The higher the thermogenic effect of any particular food, the higher your metabolic rate.
Know what you are consuming, but more importantly, know how your body will use your
consumed calories. A method of determining the “fuel mix 混合, 混和” being used has been
developed, called the respiratory 呼吸的 quotient 商数, 系数(RQ), which gives us a way
to measure the relative amounts of fats, carbohydrates, and proteins being burned for
energy.
Respiratory quotient (RQ): A method of determining the “fuel mix” being used giving us a
way to measure the relative amounts of fats, carbohydrates, and proteins being burned for
energy
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The respiratory quotient is a measure of the ratio of the volume 容量 of carbon dioxide expired
呼出, to the volume of oxygen consumed 消耗. Because the amount of oxygen used up for the
combustion 燃烧 of fat, carbohydrate and protein will be different, differences in the RQ will
indicate which nutrient source is being predominantly 显著地,突出地 used for energy purposes
用途. The formula 公式 for calculating RQ is:
RQ = volume of CO2 expired ÷ volume of O2 utilized
(Eq. 1-1)
The RQ for carbohydrates is 1.0, whereas 然而, 鉴于 the RQ for fat is 0.7. Fat has a lower
RQ value since fatty acids require more oxygen for oxidation 氧化[作用] than the amount of
carbon dioxide produced. The RQ for energy production from protein is about 0.8. The
average person at rest will have an RQ of about 0.8; however, this is from using a mixture
混合物 of fatty acids and carbohydrates for energy production, not from protein as the
number may indicate. Remember, protein/amino acids are not usually used for energy. In a
normal diet containing carbohydrate, fat, and protein, about 40% to 45% of the energy is
derived from fatty acids, 40% to 45% from carbohydrates, and 10% to 15% from protein.
However, this rate of energy production will vary depending on diet, physical activity, and
level of physical training.
Research indicates that when the diet is high in carbohydrates, the RQ is higher, and
therefore more energy is being produced from carbohydrates. When the diet is low in
carbohydrates and higher in fat, more energy is produced from fat. Additionally 此外, training
intensity will affect the energy source during exercise. Exercise rate below 60% of maximum
oxygen uptake (VO2 max) results in RQ of about 0.8, which indicates an equal 一样的 portion
部分 of energy derived from 起源 fatty acids and carbohydrates. As training intensity
increases above 60% VO2 max, more carbohydrate is used for energy. Exercise intensity at
100% VO2 max (which can only be sustained for minutes) yields a RQ of 1. You must also
keep in mind that amino acids, in particular the BCAAs (branch chain 分支链 amino acids that
aid in recovery 恢复), are also being used for energy during exercise and at rest–perhaps as
much as 10% or more during exercise.
In general, physical conditioning lowers the RQ, which means more energy is being obtained
from fatty acids in the trained individual. However, more energy is also being obtained from
protein in the trained individual. Carbohydrate is always being used for energy. For example,
when comparing the RQ of untrained individuals vs. trained individuals during exercise, the
RQ of the untrained individuals was 0.95, and the RQ of the trained individuals was 0.9. This
means that while both groups were using mostly carbohydrate for fuel during exercise, the
trained individuals were using a higher amount of fatty acids for energy. At rest, fatty acids
are the predominant 占优势的 energy source in most people; as exercise begins,
carbohydrate utilization 利用 increases. High intensity exercise uses more carbohydrate,
while low to moderate 中等的 intensity exercise uses fatty acid and carbohydrate for energy.
While this discussion of RQ is very brief, you can see that the energy substrate 酶作用物, 酶
解物 utilization of the body is quite varied 不同的,各式各样的, and both composition 组成, 成
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分 of the diet and intensity of physical activity will determine which energy substrates are
used. Therefore, it is easy to see why different sports require different dietary considerations.
The Environment and Metabolism
The outside environment also influences metabolic rate. When you are exposed 暴露的 to a
progressively 逐渐,进行性 colder climate, your body will increase its metabolic rate to keep
the body temperature constant and to prevent shivering. Shivering is invoked 引起 when the
core 核心 temperature of the body begins to drop from being in the cold. Shivering is actually
a series 连续 of involuntary 不知不觉的 muscle contractions 收缩 that are triggered 触发 to
create heat in the body, like turning on a furnace. When exposed to higher than average cold
conditions for a few days, your body actually increases its basal metabolic rate to run hotter
than average to compensate for being in a colder climate. When things begin to warm up,
even a 60 degree F day can seem extremely hot, because your metabolic rate is running at a
fast rate. After several days of acclimation to the hot climate, your metabolic rate will
decrease, and 80 degree F will feel as hot as the 60 degree F day did a few months earlier.
Exercise and Metabolic Responses
Exercise will stimulate 刺激 a series of metabolic responses that affect the body’s anatomy,
physiology, and biochemical makeup 组成.
Here are some of the changes that are stimulated by endurance exercise:

Increased muscle glycogen storage capacity

Increased muscle mitochondria 线粒体 density 密度

Increased resting ATP content 含量 in muscles

Increased resting CP content in muscles

Increased resting creatine 肌酸 in muscles

Increased aerobic enzymes 酶

Increased slow twitch muscle fiber %

Decreased fast twitch muscle fiber %

Decreased muscle size, when compared to strength training

Increased cardiac 心脏的 output 排出量

Decreased resting heart rate

Decreased body fat

Increased Krebs cycle 克雷布氏循环 enzymes

Increased capillaries 毛细血管
The magnitude 巨大 of these changes is driven 传动, 推进 primarily 主要地, 首先地 by
whether the exercise is anaerobic or aerobic. The type and duration of exercise will physically
stimulate muscles to develop more fast or slow twitch muscle fibers, and in turn 依次,轮流
dictate the primary energy mix used. High intensity exercise simulates fast twitch muscle
fiber development, while low intensity exercise results in slow twitch muscle fiber
development. There are also a series of hormonal changes that occur on an overall basis
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during exercise and non-exercising periods. These changes also are benefited and facilitated
with a nutrient profile that matches the type of metabolic flux.
Aerobic System Changes
Aerobic training greatly increases the body’s functional capacity to transport and use oxygen
and to burn fatty acids during exercise. Some of the major changes measured as a result of
aerobic exercise include:

Increased mitochondria density in slow twitch muscle fiber, which results in higher
energy production from fatty acids. Maximum oxidative capacity develops in all fiber
types.

Higher aerobic capacity.

Increase in trained muscle capacity to utilize and mobilize 动员, 调动 fat, resulting
from higher amounts of fat metabolizing enzymes, and increased blood flow.

Greater development of slow twitch muscle fibers, increased myoglobin 肌红蛋白
content, which is an iron-protein compound in muscle, which acts to store and
transport oxygen in the muscles.
Anaerobic System Changes
Anaerobic training greatly increases the body’s functional capacity for development of
explosive 爆发的 strength and maximization of short-term energy systems. Some of the
major changes measured as a result of anaerobic exercise include:

Increased size and number of fast twitch muscle fibers.

Increased tolerance to higher levels of blood lactate 乳酸盐.

Increases in enzymes involved in the anaerobic phase of glucose breakdown 打破
(glycolysis) 糖酵解(作用).

Increased muscle resting levels of ATP, CP, creatine 肌酸, and glycogen 糖原 content
含量.

Increased growth hormone and testosterone 睾酮, 睾丸素 levels after short bouts
发作 (45 to 75 minutes) of high intensity weight training.
Energy Metabolism
Energy metabolism is a series of chemical reactions that result in the breakdown of foodstuffs
食品, 粮食 (carbohydrate, fat, protein) by which energy is produced, used, and given off 发
出 as heat. Roughly 概略地, the body is about 20% efficient at trapping 捕集, 收集 energy
released. About 80% is released as heat, which explains why your body heats up quickly
when you exercise. A closer look at your muscle anatomy reveals 显示 that the mode 方式 of
energy storage 贮藏 and energy systems used is related to your physical activity.
Physical activities can be classified into four basic groups, based on the energy systems that
are used to support these activities.
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
Strength-Power: Energy coming from immediate ATP stores. Shot put, power lift,
high jump, golf swing, tennis serve, or a throw; lasting about 0 to 3 seconds of all out
effort.

Sustained 持续的-Power: Energy coming from immediate ATP and CP stores. Sprints
短距离赛跑, fast breaks 快攻, football lineman 线上球员; lasting 持续 about 0 to 10
seconds of near maximum effort.

Anaerobic Power-Endurance: Energy coming from ATP, CP, and lactic acid 乳酸. 200to 400-meter dash 短跑, 100-yard swim; lasting about 1 to 2 minutes.

Aerobic-Endurance: Energy coming from the oxidative 氧化的 pathway. Events
lasting over 2 minutes in duration.
In power events, which last a few seconds or less, the muscles depend on the immediate
energy system, namely 即, 就是 ATP and CP reserves 储量. In speed events, the
immediate and non-oxidative, or glycolytic 糖酵解的 energy sources are utilized. In
endurance events, the immediate and non-oxidative energy sources are used, and the
oxidative energy mechanisms 机理, 原理 become a more important source of energy.
ATP and CP are replenished 把...重新补足 from energy derived from complete breakdown
of glucose, fatty acids, and some proteins.
ATP Production
ATP is the molecule that stores energy in a form that can be used for muscle contractions.
Energy production then revolves around rebuilding ATP molecules after they are broken down
for energy utilization. Our muscle cells store a limited amount of ATP. During exercise our
bodies require a constant supply of ATP to provide the energy needed for muscular
contraction; therefore, metabolic pathways must exist in the cell with the ability to produce
ATP rapidly. Our muscle cells can produce ATP by any one of or a combination of three
metabolic pathways: the ATP/CP pathway, glycolytic pathway and/or oxidative
pathway.
ATP/CP pathway:
ATP and CP provide anaerobic sources of phosphate-bond energy. The energy liberated from
hydrolysis (splitting) of CP re-bonds ADP and Pi to form ATP.
Glycolytic pathway: Glucose is broken down to produce energy anaerobically.
Oxidative pathway: Oxygen combines with lactic acid resynthesizing glycogen to produce
energy aerobically.
The ATP/CP Energy Pathway
This pathway is anaerobic, meaning it requires no oxygen for energy use. Such a pathway is
demonstrated in sports that require ballistic 射击的,冲击的, explosive strength or maximum
efforts for short periods of time (shot-putting, pitching, weightlifting and powerlifting for
example).
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ATP 三磷酸腺甙 (adenosine 腺甙 triphosphate 三磷酸盐) is the energy source for all human
movement. The release of one of the three phosphate 磷酸盐 molecules provides the energy
for human movement. Unfortunately, muscle cells only store a limited supply of ATP that is
readily 迅速地 available for use (only 5 mmols 摩尔 per kg of muscle). In maximum efforts it
is totally gone within 1.26 seconds! However, all activities regardless 无论如何 of their
intensity or length will start with this pathway. With the help of an enzyme called myosin 肌
浆球蛋白, 肌凝蛋白 ATPase 腺苷三磷酸酶, ATP loses one phosphate 磷酸盐 molecule in order
to release energy:
ATP ADP + Pi + Energy
(Eq. 1-2)
For short-term, high-intensity activities like shot putting or throwing, this is enough. Further
use in this pathway, however, requires that the ADP be resynthesized back to ATP with the
help of creatine phosphate (CP) 肌酸磷酸盐 and an enzyme called creatine kinase 肌酸激酶:
ADP + CP ATP + Creatine
(Eq. 1-3)
Like ATP, CP is stored in small amounts (16 mmols per kg of muscle). As seen in Figure 3-3,
CP stores fall rapidly after 10 seconds of maximal activity and are usually completely depleted
耗尽 in under 60 seconds.
Whether or not you can increase your resting levels of ATP through training has not widely
been studied or understood. Research has suggested that it is possible through both weight
training and aerobic training. However, this is mainly because of fiber hypertrophy 肥大 and
thus, more ATP can be stored in Type II than Type I fibers (considering the size and growth
potential of Type II fibers).
Perhaps an even bigger question than “how much?” or “can you increase?” is “how quickly
can ATP and CP stores be replenished?” Though 然而 there will be individual differences,
research has shown that ATP stores can be fully restored within 3.5 minutes and CP stores
can be fully replenished within 8 minutes.
The Glycolytic Pathway
Like the ATP/CP pathway, the glycolytic pathway is also anaerobic. Once you have depleted
the readily available ATP/CP stores, the body must break down carbohydrates to produce
more ATP. This process uses either glycogen (which is stored in the muscle cells) or glucose
(which is found in the blood) to convert ADP back into ATP with the waste product being lactic
acid:
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Glucose + 2Pi + 2ADP + 2NAD+ 2 lactic acid + 2ATP + 2NAD
(Eq. 1-4)
This lactic acid eventually builds more quickly than it can be flushed 奔涌 out of the muscle to
the point of the anaerobic threshold 阈, 界限, otherwise 不同地 known as muscular fatigue
疲劳. At this point, you must either stop or slow down until the lactic acid is removed. Lactic
acid is converted to a less toxic 有毒的 form called lactate 乳酸盐 which is used either as an
energy substrate 酶作用物 or to produce more glucose (a process called gluconeogenesis 糖
异生).
Stored sugars are rarely ever depleted (and are never depleted in the glycolytic pathway).
However, this is not the limiting factor; the limiting factor is the accumulation 蓄积, 累积 of
lactic acid. Generally, the glycolytic pathway ends under maximal conditions at around 80
seconds before the oxidative pathway (and lower levels of activity) takes over.
How well your muscles function in the glycolytic pathway is determined by several things:
1. How quickly you can get rid 免除 of the lactic acid.
2. How well you can tolerate 宽容, 容许 the pain caused by lactic acid.
3. How far you can go before that pain comes and it becomes vital to get rid of the lactic
acid (the anaerobic threshold).
Blood lactate levels usually return to normal within an hour after activity. Research shows
that training can increase the rate in which lactic acid is removed as well as push back the
anaerobic threshold. As for your ability to tolerate the pain, THAT comes with experience!
The Oxidative Pathway
This system is aerobic, meaning it uses oxygen to produce ATP via the Krebs cycle and
electron 电子 transport chain. Ultimately 最终, more ATP is produced through this pathway
than through the other two; however, it takes much longer. Pyruvate 丙酮酸盐, which is
produced through glycolysis, undergoes 经历 a long trip through the Krebs cycle to convert
several coenzymes 辅酶 that have lost an electron back into their originalstate 开始,发源. It is
in the electron transport chain where these coenzymes undergo oxidation to convert ADP
back into ATP. In the end, up to 38 molecules of ATP can be produced through the oxidative
pathway.
Pyruvate: A byproduct 副产品 of glycolysis.
It is only in this pathway that fat can be used for energy. Breaking down fat for energy is also
a long process (called beta oxidation), which does not directly produce ATP. Rather, it
provides the coenzymes needed for the Krebs cycle. Scientists have estimated that while at
rest (and in the oxidative pathway) 70% of energy comes from fat, not carbohydrates or
protein.
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However, as exercise intensity increases, more and more carbohydrates are used instead of
代替 fat (beta oxidation can’t keep up). In fact, at the upper limits of the aerobic pathway,
100% of the energy is coming from carbohydrates — not fat! If at these levels carbohydrates
aren’t available, the body will indeed 的确,当然 catabolize (使)异化, (使)发生分解代谢 the
very muscle it’s using for energy.
Beta oxidation: A series of reactions in which fatty acids are broken down.
How the Systems Interact
To better understand how each of these energy systems relate to each other, let’s take a look
at what happens when muscles contract. First, we will take a look at the immediate energy
systems. The brain sends a signal along the nerves which triggers a release of calcium 钙 ions
离子 in the muscles, which stimulates the muscles to contract, and in the process, the high
energy molecule ATP (adenosine triphosphate) releases energy and is reduced to adenosine
diphosphate plus one phosphate atom. In this way, the immediately available ATP stores are
depleted very rapidly, the first few seconds of a maximum muscle contraction.
The second immediate source of cellular energy is creatine phosphate (CP). There are several
more times CP molecules in the cell than ATP. Creatine phosphate serves to instantaneously
即刻, 立即 regenerate 再生 ATP molecules. Therefore, the ATP that is broken down to ADP
腺苷二磷酸 during muscle contraction is restored to the high energy ATP by CP. The third
immediate energy system enables the cell to regenerate ATP from two ADP molecules,
resulting in one ATP and one AMP (adenosine monophosphate) molecule. This immediate
energy source is depleted in a matter of seconds under conditions of all-out effort, under
conditions of maximum muscle contractions.
It is interesting to note that the storage capacity of ATP and CP in a cell is quickly reached for
a particular muscle size. In order to increase the amount of ATP and CP on hand, the muscle
fibers must increase in size. This is why power athletes get big muscles. The workload 工作
量 demands 需要 that more ATP and CP are on hand. To meet this demand, the muscle fibers
increase in size, causing the entire muscle to get big. When you train, different energy
systems are conditioned to work best at the particular workload imposed on the muscles.
As the immediate energy supply is quickly depleted through high intensity physical activity,
the non-oxidative energy source kicks in. The non-oxidative system is a major contributor
贡献者 of energy during 4 to 50 seconds of effort. Non-oxidative metabolism (glycolysis)
involves the breakdown of glucose to regenerate ADP into ATP. Muscle tissue is densely 浓密
地 packed 充满...的 with non-oxidative enzyme systems. Chemically 以化学方法, what
happens is that the glucose molecule is split 分裂 in half, and energy is released. This energy
is enough to regenerate 2 ATP molecules and leave two pyruvate 丙酮酸盐 molecules. In
general, these pyruvate molecules are immediately converted to lactic acid molecules. The
amount of free glucose is generally low in the cells, so glucose is derived from the breakdown
of glycogen.
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Fast twitch muscle fibers, those associated 联合的 with strength and size, are also referred to
as fast glycolytic muscle fibers because they house the metabolic machinery to get quick
energy through fast glycolysis pathways. The fast twitch fibers have a low capacity for
oxidative metabolism and are instead set up to run glucose through their fast glycolysis
pathways. Lactic acid then builds up because it is being produced too rapidly to enter into the
oxidative pathways. Lactic acid is then cleared 清除 from the muscle, fed into the bloodstream
血流, taken to the liver, and there made into glucose and glycogen. Glycolysis takes place in
the cytoplasm 细胞质 of the cell.
For physical activities lasting more than 2 minutes in duration, the oxidative metabolic
pathways produce the majority of energy to maintain muscle contractions. Potential
oxidative energy sources include glucose, glycogen, fats, and amino acids. Oxidative energy
production takes place in the mitochondria 线粒体 of the cells. Far more energy is produced
when glucose is completely broken down in the mitochondria. Glucose is still first split in half
by glycolysis. The pyruvate molecules then enter into the mitochondria where they are
completely broken down. The oxidative pathways are called the Krebs cycle and electron
transport. Fatty acids, from fat, are a major energy source during endurance events. The
processes of fat utilization are activated more slowly than carbohydrate metabolism and
proceed at a lower rate. Fatty acids are activated and combined with the molecule carnitine
卡尼汀/肉毒硷, which enables them to be transported into the mitochondria.
Krebs cycle: Citric acid 柠檬酸 cycle; a set of 8 reactions, arranged in a cycle, in which free
energy is recovered in the form of ATP.
Electron transport: The passing of electrons over a membrane 薄膜 aiding in a reaction to
recover free energy for the synthesis 合成 of ATP.
Glycogen Depletion and Metabolism of Fatigue
Glycogen is essential to performance for both anaerobic and aerobic activities. Muscles being
strenuously 奋发的, 费劲的, 艰苦的 exercised will rely on 依靠 glycogen to power these
strength-generating 产生的, 生成的 muscle contractions. In endurance exercise, while the
primary fuel is fatty acids, glycogen is also utilized. In fact, fat catabolism 分解代谢 works
better when carbohydrates are being metabolized. Studies on long-term exercise and work
performance all indicate the onset 开始 of fatigue when glycogen is depleted. This again
underscores 底线 the importance of adequate 适当的, 足够的 carbohydrate intake and
glycogen replenishment 把...重新补足. Glycogen depletion is just one factor that contributes
to the onset of fatigue. The following lists several other fatigue causing factors that athlete is
faced with:

ATP and CP depletion

Lactic acid accumulation

Calcium ion build-up 增进 in muscles

Oxygen depletion

Blood pH decrease
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Monitoring Your Metabolism
Until recently, there were no affordable 普及型 and easy-to-use home testing methods that
were designed for athletes to measure key metabolic parameters 参数. Early in 1990,
inventor Robert Fritz developed the first useful metabolic testing tool for athletes, NitroStix™.
After rigorous 精确的 testing, and confirmation by the eminent 杰出的 sports physiologist 生
理学家 Dr. Thomas D. Fahey, author of the ISSA’s new Youth Fitness Trainer Program and the
ISSA’s new Specialist in Strength and Conditioning, this home testing device 装置 was made
available to the general public. The NitroStix™ made it possible for athletes to monitor their
nitrogen 氮 balance on a daily basis. The significance of this product cannot be overstated
夸张. By measuring your state of nitrogen metabolism you can determine if your protein
intake is sufficient 充分的, 足够的 and also if certain supplements are being ingested 摄取 in
sufficient amounts to improve nitrogen balance. On the horizon is the newly developed
testing device that combines nitrogen balance testing with fat metabolism status 状态. These
home tests measure the output of metabolic waste 消耗 products in urine 尿. They are very
easy to use and offer a means to really fine tune 微调 your training and nutrition program.
Also developed by B. Fritz and Dr. Fahey is a testing method that was probably the Russian
athletes’ best kept secret. This new test provides an economical way to determine
testosterone 睾酮, 睾丸素 and cortisol 可的索, 皮质醇, 氢(化)可的松 levels in the body by
analysis of saliva 唾液. When the body is overtrained, cortisol levels are increased. Cortisol is
a catabolic hormone that stimulates the breakdown of muscle tissue. High amounts in the
blood ultimately lead to tissue wasting and negative nitrogen balance. So when the
testosterone/cortisol ratio is high, anabolism 合成代谢 is prevailing 占优势的. However, when
cortisol levels are high and the ratio is lowered, this is an indication of overtraining. By testing
your testosterone/cortisol ratio, you can determine if you are in a state of over training or not.
In this way, you can determine how hard you should train, if you should take a few days off,
or if training intensity should increase.
In addition handheld portable indirect calorimeters 测热计, 热量计 that measures oxygen
consumption (VO2) and determine resting metabolic rate (RMR) are being used in the
medical field as well as many fitness facilities today. The rate of oxidation or the burning of
the calories is different for fats, carbohydrates and protein as discussed earlier in the unit.
The food you eat can either be burned to liberate energy, converted into body weight, or it
can be excreted 排泄, 分泌. If you light a candle and then place a dome 圆顶 over the candle
cutting off the fires source of oxygen, the fire will go out. In the same way our body’s ability
to undergo oxidation is contingent 偶然的, 意外的, 应急的 on oxygen. If we are getting more
oxygen then we should be burning more calories. All foods release heat when they are burned.
This release of heat is measured in kilocalories. A calorie is a unit of heat. Practically 事实上
speaking this unit is too small to be useful, therefore the kilocalorie is the preferred unit in
metabolite studies. Not all foods are burned completely to produce energy. Some of them are
only partially degraded 退化的 to provide building blocks 阻断 to support repair and growth.
Generally speaking, the calories coming from protein are used for maintenance, repair, and
growth of new tissues and organs. Calories from carbohydrates are used for energy. Calories
from conventional 常规的 sources of a fat are prone to be stored as fat since it already has the
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same molecular structure as body fat. The heat liberated from a particular food is thus a
measure not only of its energy content but also of its tendency to be burned as heat. This is
known as the thermogenic 生热的 effect. Nutrition monitoring plays a vital role in the care of
patients with diabetes 糖尿病; 多尿症, heart disease, high blood pressure, and obesity 肥胖,
as well as conditions that place patients at risk for malnutrition 营养不良, such as cancer,
burns 灼伤, 烧伤, trauma 创伤, 外伤, infection 传染, 感染, obstructive 引起阻塞的 lung
disease, and HIV. Indirect calorimeters 测热计, 热量计 can be used in acute 急性的 care,
long-term care, home care, and clinic-based care settings such as physician offices,
rehabilitation centers, and ambulatory 能走动的, 不卧床的 surgery 手术 centers and fitness
based facilities.
Conclusion
We need energy to maintain the many chemical and physical activities of the body. As we
have learned, all energy comes from the sun. Plants use this solar 太阳的 energy to perform
chemical reactions to form carbohydrates, fats and protein. Humans, like animals, consume
plants and other animals to obtain the energy required to maintain cellular activities. These
cellular activities known as metabolism are maintained under homeostatic controls. These
many chemical reactions occurring in our bodies must be regulated to maintain a balance
between the trillions of cells in our body. These cells maintain balance through an intricate
organization system. We will now discuss this intricate 复杂的 organized system known as the
body.
Summary
We need energy to maintain the many chemical and physical activities of the body. All energy
comes from the sun. Plants use solar energy to perform chemical reactions to form
carbohydrates, fats and protein. Humans like animals consume plants and other animals to
obtain the energy required to maintain cellular activities.
I. The body’s components work together in a highly organized manner to maintain a balance,
this balance is known as homeostasis.
A. Metabolism can be defined as all of the chemical processes that occur in
the body. Metabolism is categorized into two general phases; anabolism
(building phase) and catabolism (breaking down phase).
B. The food you eat can either be burned to liberate energy, converted into
bodyweight, or excreted.
1.The calories coming from protein are used for maintenance, repair, and
growth of new tissues and organs. Calories from carbohydrates are
used for energy. Calories from conventional sources of a fat are
prone to be stored as fat since it already has the same molecular
structure as body fat.
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II. Energy metabolism is a series of chemical reactions that result in the breakdown of
foodstuffs (carbohydrate, fat, protein) by which energy is produced, used, and given off as
heat.
A. ATP, an acronym for adenosine triphosphate, is the molecule that stores
energy in a form that can be used for muscle contractions.
1.Our muscle cells can produce ATP by any one or a combination of three
metabolic pathways: the ATP/CP pathway, glycolytic pathway and/or
oxidative pathway.
2.The formation of ATP without oxygen is known as anaerobic
metabolism. This includes the ATP/CP and the anaerobic glycolytic
pathway. Short-term activities at higher intensities utilize ATP
production from anaerobic energy pathways.
a. In the ATP/CP system, the P (phosphate) is separated
from the C (creatine) and combines with ADP (adenosine di-,
meaning two, phosphates) to reform ATP (adenosine tri-,
meaning three, phosphates). One molecule of CP results in
the reformation of 1 molecule of ATP. This system is sufficient
for 3 to 15 seconds of ATP production.
b. In non-oxidative glycolysis, glucose or glycogen is
converted to lactic acid. One molecule of glucose results in 2
molecules of ATP and 1 molecule of glycogen results in 3
molecules of ATP. This system is reliable for 1 to 2 minutes of
all out effort.
3. The formation of ATP with oxygen is known as aerobic metabolism. This
includes the aerobic glycolytic pathway and the oxidative pathway.
Long-term activities with a low to moderate intensity utilize ATP production
from aerobic sources.
a. The aerobic metabolism of 1 molecule of glucose results in the
production of 38 molecules of ATP and 1 molecule of glycogen results in the
production of 39 ATP.
4. Glycogen is essential for both anaerobic and aerobic activities. Muscles
being strenuously exercised will rely on glycogen to power strength
generating muscle contractions. In endurance exercise, while the primary
fuel is fatty acids, glycogen is also utilized.
5. Monitoring your metabolism is possible through Nitrostix or handheld,
portable, indirect calorimeters.
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