Bioenergetics is the part of Biochemistry concerned with the energy involved in growth, development and metabolism.
If oxygen is available, a large amount of ATP is formed. This is known as aerobic glycolysis.If inadequate oxygen is available to meet the energy demands of the exercise task, then insufficient ATP is formed and lactic acid is a by-product of the process to generate more ATP. This is known as anaerobic glycolysis.
Creatine phosphate (PCr) rapidly replaces the ATP and becomes the next major source of energy.The anaerobic breakdown of muscle glycogen through glycolysis to form ATP and lactic acid predominates after PCr, whilst aerobic processes predominate from approximately 60 s and beyond.
sports require specific sources of
The body stores energy in a variety of ways—
in ATP, PCr, muscle glycogen,etc
In order for this energy to be used,it must
undergo certain biochemical reactions in the
biochemical reactions serve as a basis
for classifying human energy expenditure by
three energy systems:
the ATP-PCr system(phosphagen system)
the lactic acid system
the oxygen system
Also known as the phosphagen system.
ATP is the immediate source of energy for
almost all body processes.
ATP-PCr system is critical to energy
The value of the ATP-PCr system is its ability
to provide energy rapidly.
sport events such as competitive weight
lifting or sprinting 100 meters.
power is a term often associated
with the ATP-PCr energy system.
Cannot be used directly as a source of
energy for muscular contraction.
it can help replace ATP rapidly when
glycogen must be broken down to
glucose, which undergoes a series of
reactions to eventually form ATP, a process
glycolysis is the scientific term
for the lactic acid energy system.
is used in sport events in which energy
production is near maximal for 30–120
seconds, such as a 200- or 800-meter run.
lactic acid system has the advantage of
producing ATP rapidly.
lactic acid produced as a by- product
may be involved in the onset of fatigue.
known as the aerobic system.
exercises are designed to stress the
oxygen system and provide benefits for the
heart and lungs.
oxygen system cannot be used directly
as a source of energy for muscle
contraction, but it does produce ATP in large
quantities from other energy sources in the
glycogen, liver glycogen, blood
glucose, muscle triglycerides, blood FFA and
triglycerides, adipose cell triglycerides, and
body protein all may be ultimate sources of
energy for ATP production and subsequent
a complex series of reactions
metabolic by-products of
carbohydrate, fat, or protein combine with
oxygen to produce energy, carbon
dioxide, and water.
whole series of events of oxidative
energy production primarily involves aerobic
processing of carbohydrates and fats through
the Krebs cycle and the electron transfer
rate of ATP production is lower.
major advantage of the oxygen system
over the other two energy systems is the
production of large amounts of energy in the
form of ATP.
process may be adequate to handle mild
and moderate levels of exercise but may not
be able to meet the demand of very
oxygen system is used primarily in sports
emphasizing endurance, such as distance
runs ranging from 5 kilometers (3.1 miles) to
the 26.2-mile marathon and beyond.
energy processes take place in the
mitochondria of cells.
steady-state exercise, the pyruvic
acid produced is converted to acetyl-CoA in
the mitochondria and then undergoes aerobic
are another major source of energy
during prolonged exercise and can only be
used to produce energy using aerobic
of the three energy systems can
generate power to different capacities and
varies within individuals.
estimates suggest that the ATP-PCR
system can generate energy at a rate of
roughly 36 kcal per minute. Glycolysis can
generate energy only half as quickly at about
16 kcal per minute. The oxidative system
has the lowest rate of power output at about
10 kcal per minute.
three energy systems do not work
independently of one another.
very short, very intense exercise, to
very light, prolonged activity, all three
energy systems make a contribution
however, one or two will usually
factors of any activity carried out affect
energy systems more than any other variable
they are the intensity and duration of
In the year 2000, Noakes and colleagues questioned
the classical model of energy systems.
Their argument centered around these key issues:
The heart and not skeletal muscle would be
affected first by anaerobic metabolism.
No study has definitively found a presence of
anaerobic metabolism and hypoxia (lack of oxygen)
in skeletal muscle during maximal exercise.
The traditional model is unable to explain why
fatigue ensues during prolonged exercise, at
altitude and in hot conditions.
Cardiorespiratory and metabolic measures such as
VO2max and lactate threshold are only modest
predictors of performance.
an attempt to produce a more holistic
explanation, Noakes developed a model that
consisted of five sub-models:
The classical 'cardiovascular / anaerobic'
model as it stands now.
The energy supply / energy depletion
The muscle recruitment (central fatigue) /
muscle power model.
The biomechanical model.
The psychological / motivational model.
Any energy requiring processes invariably uses
ATP as the prime source of energy.
At the start of an activity the initial source of
energy is from ATP stores at the muscle
The amount of ATP in muscle is rather small.
This amount of ATP in muscle has been estimated
to be sufficient to fuel around 3–5 seconds of
maximal effort if ATP was the sole energy
other immediate source of energy for
high intensity exercise is that of creatine
phosphate or phosphocreatine (PCr).
phosphate (PCr) rapidly replaces
the ATP and becomes the next major source
amount of PCr is sufficient to fuel
maximal exercise solely for approximately 6–
essential store of carbohydrate fuel for
both high- intensity exercise and prolonged
muscle glycogen stores have a
concentration of 350 mM kg–1 dry muscle.
be increased signiﬁcantly by a high
carbohydrate diet and reduced signiﬁcantly
by repeated bouts of sprinting or a single
prolonged bout of exercise or when on a low
carbohydrate diet for around 2–4 days.
muscle glycogen breaks down to
produce energy, under the inﬂuence of the
enzyme glycogen phosphorylase.
process of breaking off glucose
molecules from glycogen is known as
is a series of processes which takes
place in the cytoplasm of cells resulting in
the formation of two pyruvic acid molecules
the activity is intense, the pyruvic acid
leads to the formation of lactic
acid, although during steady-state exercise
the majority of the pyruvic acid formed is
broken down to produce carbon dioxide and
delivered to the muscle by blood
may also act as a useful energy source during
nutrition forms the foundation for
Six broad categories of nutrients:
a rapid and readily available source
in three forms:
monosaccharides, disaccharides, and
is the most important simple sugar
and is the only form of carbohydrate that can
be directly metabolized to obtain energy.
is not found in plants and is the
polysaccharide form in which animals store
exercise, glucose molecules can be
removed from glycogen in the liver by
glycogenolysis, and released into the
bloodstream to provide glucose as a
metabolic substrate to other cells of the
and glycogen are the carbohydrates
important for metabolism at rest and during
During exercise, muscle cells can obtain
glucose by absorbing it from the bloodstream
or by glycogenolysis from intramuscular
glycogenolysis in the liver can maintain blood
glucose levels during exercise and at times of
rest between meals.
rest, carbohydrate is taken up by the
muscles and liver and converted
can be used to form ATP and in the
liver it can be converted into glucose and
transported to the muscles via the blood. A
heavy training session can deplete
carbohydrate stores in the muscles and liver.
can release energy much more
quickly than fat.
is stored predominantly as adipose tissue
throughout the body and is a substantial
is less accessible for cellular metabolism as
it must first be reduced from its complex
form, triglyceride, to the simpler
components of glycerol and free fatty acids.
although fat acts as a vast stockpile of
fuel, energy release is too slow for very
is used as a source of
energy, particularly during prolonged
however it must first be broken down into
amino acids before then being converted into
glucose. As with, fat, protein cannot supply
energy at the same rate as carbohydrate.
mineral supplements above
recommended levels on an acute or chronic
basis does not benefit exercise performance
or enhance trainin responsiveness.
water and electrolyte loss impairs
heat tolerance and exercise performance and
can trigger heat cramps, heat exhaustion, or heat stroke.
practice or competition, an athlete
sweats up to 5 kg of water.
corresponds to about 8.0 g of salt
depletion because each kilogram of sweat
contains about 1.5 g of salt (of which 40%
replacement of water lost
through sweating should become the
factors determine the total daily
energy expenditure (TDEE):
1. Resting metabolic rate
2. Thermogenic influence of consumed food
3. Energy expended during physical activity
minimum energy requirement that sustains
the body’s functions in the waking state.
oxygen uptake under the following
three standardized conditions quantifies this
requirement called the basal metabolic
1. No food consumed for a minimum of 12
hours before measurement
2. No undue muscular exertion for at least 12
hours before measurement
3. Measured after the person has been lying
quietly for 30 to 60 minutes in a dimly
lit, temperature- controlled room.
is measured under less strict conditions
(e.g., 3 to 4 hours after a light meal without
of energy expenditure during rest
and during exercise are often based on
measurement of whole body oxygen
consumption (VO2) and its caloric
resting conditions, an average person
consumes about 0.3 L of O2/min. or 18L of
O2/hr. or 432L of O2/day.
standardized measure of energy
expenditure at rest is BMR.
Factors affecting BMR are:
Body surface area
of a normal individual varies from 1200
to 2400 Kcal/day.
expenditure for athletes engaged in
intense training can exceed 10000Kcal/day.
expenditure can be measured using
one of the three approaches:
Isotope dilution, doubly labelled water
of Exercise Physiology, fourth
edition, Victor L. Katch,William D.
McArdle, Frank I. Katch.
Exercise Physiology Integrating Theory and
Application, William J. Kraemer, Steven J.
Fleck, Michael R. Deschenes.