NASM essentials of sports performance training
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NASM essentials of sports performance training

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is typically around 6 L/min at rest and approximately
20\u201325 L/min during maximum exercise. For the aerobic elite (e.g., cross-country skiers, rowers,
cyclists) it may be over 40 L/min.
The chemical reactions that transform energy in the cells of the body are collectively known
as metabolism. It has been estimated that if you could put all the ATP of the body into a glass,
The process which brings oxy-
gen from the air, across the
alveolar membrane, and into
the blood to be carried by he-
Cardiac Output
The amount of blood
the heart pumps per minute.
Stroke Volume
The amount of blood
pumped with each contraction
of the ventricles.
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that glass might be between a shot glass and a small juice glass. With such a small amount of ATP
at any time, the body must continually produce ATP. For our purposes, metabolism is to supply
the energy needed to carry out the mechanical work of muscular contraction across the intensity
spectrum (1,2).
Aerobic exercise requires the body to take oxygen from the atmosphere, deliver it to the lungs,
transfer it into the blood, and pump it to the working muscles where it is utilized to oxidize car-
bohydrates and fats in order to produce ATP. The energy pathway is often termed the oxidative
(oxygen) system and involves several body systems, including the respiratory, cardiovascular,
muscular, and endocrine systems.
Through a complex series of chemical reactions, glycogen and fats are broken down in the
presence of oxygen to provide energy to be transferred into ATP. During rest and low-intensity
activity, the energy required for muscle contraction comes almost entirely from the aerobic pro-
duction of ATP. 
Most cells (including muscle fibers) contain mitochondria, which is the site of aerobic ATP
production. The greater the number and volume of mitochondria, the greater the cell\u2019s aerobic
energy production capabilities. During prolonged exercise, more than 99% of the energy re-
quired is generated by aerobic reactions. These aerobic pathways provide the major supply of
energy to all cells of the body through the metabolism of circulating glucose, stored fats, and
stored carbohydrates. Because the amount of stored carbohydrates is limited, one of the most
important adaptations to training is the shift by the body from the use of carbohydrates to
stored fat as a primary fuel for energy (1,2). 
When the muscles are being used aerobically, they use both fat and glucose to produce ATP.
The aerobic system produces much more ATP than the anaerobic system and gains far more ATP
when using fat as a fuel. This is primarily because of the ability to convert fat, which yields nine
calories of energy per gram, whereas glucose and protein yield only about half that amount. Ad-
ditionally the waste products of aerobic ATP production are water and CO2, which are both eas-
ily processed by the body, making aerobic energy production the more efficient method of gen-
erating energy and averting muscle fatigue (1,2) (Fig. 5.1).
Anaerobic metabolism is the ability of the body to produce energy by metabolizing carbohydrates in
the absence of oxygen. With increasing exercise intensity, the cardiorespiratory system makes every
attempt to increase its delivery of oxygen to the mitochondria of the exercising muscle fibers to pro-
duce enough ATP aerobically. When increasing intensity, at some point the cardiorespiratory
system becomes unable to supply enough oxygen to the exercising muscles and energy production
fails to meet energy needs. This means the body has to increase its reliance on the anaerobic systems
f m
f e
n ATP store
ATP-CP store
Lactic acid system
Aerobic system
Overall performance
2 secs 10 secsT T 1 min 2 hrs
FIGURE 5.1 Energy systems: Anaerobic (ATP,ATP-CP, Lactic acid) and Aerobic 
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to produce the ATP rapidly enough to meet these energy needs. The intensity level at which oxy-
gen supply is unable to match the energy demands is referred to as the anaerobic threshold. It has
also been termed lactic threshold. Even though these terms are often used interchangeably, true lac-
tic threshold occurs before the anaerobic threshold. The academics of how this is actually deter-
mined and the difference between the two concepts is beyond the scope of this chapter.
In brief, the lactic threshold is determined by serial blood analysis at increasing intensities
of exercise while the anaerobic threshold can be determined through submaximal VO2 testing
(such as the step test discussed in Chapter 3). Although the measurement of oxygen consump-
tion requires some technical expertise and equipment, it is still more practical in the performance
setting due to its ease of use versus the understandable reluctance of athletes to have repeated
blood samples taken (1,2). 
The primary fuel for anaerobic ATP production is glucose that is stored in muscles and the
liver as glycogen, a large molecule made up of chains of glucose. This energy pathway is often re-
ferred to as the glycolytic (or lactic acid) system. During muscle contraction, stored glucose is
broken down into lactic acid. During this breakdown of glucose, a small number of high-energy
ATP molecules are produced. It is estimated that if glycolysis was the sole source of fuel for exer-
cise, one could only continue for roughly one minute.
A second source of anaerobic ATP production is creatine phosphate (CP). The CP molecule is
also a high energy compound. Once a ATP has been split and its energy released for mechanical
work by the muscle, the energy in the CP molecule can be quickly transferred to the \u201cused\u201d adeno-
sine diphosphate (ADP) and a free phosphate molecule is attached making a new ATP. This energy
pathway is often referred to as the ATP-CP system. As with the muscle\u2019s store of ATP, there is an ex-
tremely limited supply of creatine phosphate. If this was the sole source of energy, exercise might
be sustained for maybe 10\u201315 seconds. 
At no time is only one system functioning. All three systems are supplying energy constantly.
Which one is the prominent system depends on the duration and intensity of exercise, as seen in
Table 5.1.
In skeletal muscle, this cycle goes on constantly at the myosin cross bridges and must be
constantly resupplied by ATP from glycolytic and aerobic energy sources. The main advantage of
the ATP-CP system is the speed at which energy can be supplied. The main drawback is that not
as much ATP can be produced as with the aerobic system. If glycolysis is the prominent source
of ATP, the result is an increasing level of lactic acid waste that can inhibit exercise. These anaer-
obic energy pathways are the main source of energy for high-intensity, short-duration activities
Lactic acid is continuously being produced and removed, even when the body is at rest.
When lactic is produced faster than it is removed, it spills out into the blood and symptoms of
fatigue become evident. A major goal of training should be to minimize lactic acid production
while enhancing lactic acid removal during exercise (2). One way to accomplish this is through
a combination of high intensity interval training and prolonged submaximal training. Interval
training helps maximize cardiorespiratory adaptations and increases VO2 max (3). The more oxy-
gen that is consumed, the less that will be reliant on the anaerobic (especially glycolytic) break-
down of carbohydrates. Prolonged submaximal training can help to induce an increase in mito-
chondrial structure and function. These adaptations