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Energy Systems, Energy for Sports performance & movement

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Horace Reid Dennis

on 18 September 2015

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Transcript of Energy Systems, Energy for Sports performance & movement

Energy Systems, Energy for Sports performance & movement
The body's energy sources
All movement requires a series of coordinated muscle contractions, which in turn requires a supply of energy.

For movement to occur the body must transfer stored chemical energy to mechanical energy.

The chemical energy required of a cell is supplied by the breakdown of Adenosine Triphosphate (ATP) - A high energy compound
ATP
Molecules of ATP consist of atoms held together by a set of bonds which store energy.

It is the breaking of splitting of the outermost bond that release the energy used to fuel all the processes within the body, and in particular, the contractions of skeletal muscles which facilitates the movement.
ATP
It is the splitting of ATP, for example, that releases the energy to stimulate the myosin cross bridge attachment to the active site on the actin filament during the sliding filament theory of muscular contraction, which we will cover next!!

Something to note
- The stimulus for ATP splitting is the enzyme
ATPase
and that since energy is given off, some in the form of heat, it is known as an
exothermic reaction.
ATP
There is, however only a
limited amount
of this high energy compound in the muscle cell, which is sufficient only to produce several powerful contractions; or in practical context, to run as fast as you can for a few seconds.

ATP must therefore be constantly
resynthesised
in order to provide a continuous supply of energy.
ATP
ATP re-synthesis at rest or during prolong steady state exercise occurs via aerobic metabolism - the breakdown of carbohydrate and fat in the presence of oxygen.

But this process is
rather slow
, and
cannot meet the demands of high intensity exercise
, such as a 100m sprint where the body where the body requires energy very rapidly. The body has therefore adapted several ways in which to re-synthesise ATP to ensure a continuous supply of energy.
Introduction
Where do muscles get the energy to provide movement?
Energy is fundamental to the study of sport and as such, this topic will examine the sources of energy for muscular contraction and in particular the role of Adenosine Triphosphate (ATP), Carbohydrates and fats in energy provision
ATP
There are three basic pathways or energy systems which
govern the replenishment of ATP
and therefore energy supply. Which system operates is largely dependent upon how immediate the energy is required, how intense the activity and whether or not oxygen is present.

The three energy systems are:

(1) The alactic or ATP-PC system
(2) The lactic acid system
(3) The aerobic system
ATP
Muscle Contraction
Circulation
Tissue Building
Nerve Transmission
Digestion
The Alactic/ATP-PC system
The is the first of the
anaerobic pathways
, implying that
oxygen is not directly used
.

This pathway involves the rapid regeneration of ATP through another energy rich compound existing in the muscles, named
creatine phosphate

(also known as phosphocreatine, PC
).

Creatine phosphate is broken down in the sarcoplasm of the muscle cell due to the action of the enzyme
creatine kinase
. Creatine Kinase is stimulated by the increase in free phosphates (Pi) resulting from the breakdown of ATP into ADP + Pi + energy.
The Alactic/ATP-PC system
Unlike ATP, the energy derived from the breakdown of phosphocreatine is not directly used for muscle contraction, but instead rebuilds ATP so that is can once again be broken down to maintain a constant supply of energy.

This an
endothermic reaction
as energy is consumed by ADP + Pi to form ATP.
The Alactic/ATP-PC system
Once ATP has been broken down to give adenosine diphosphate, a free phosphate and energy which is used for muscular work, it must be resynthesised for further use.

Since ATP resynthesis requires energy itself, phosphocreatine is broken down almost simultaneously to provide the energy for ATP resynthesis, by using this energy to rejoin the free phosphate back on to ADP to once again form ATP -

This is known as a couple reaction
The Alactic/ATP-PC system
Feature of the system:

The main problem with this system, is that like ATP-PC is very limited within the muscle (although there is approximately four times the amount of PC than ATP), and its levels fall as it is used to replenish the depleted ATP.

Fatigue occurs when phosphocreatine levels fall significantly and they can no longer sustain ATP resynthesis.

This usually occurs after 8-10 seconds of maximum effort, such as that which occurs in a flat out 100m sprint.
The Lactic Acid pathway
Once PC has been depleted within the muscle, ATP must be resynthesised from another substance -
GLYCOGEN
.

Carbohydrate is eaten in form of sugar or starch and is stored in the muscles and the liver as glycogen.


Before glycogen can be used to provide energy for ATP re-synthesis, it must be converted to the compound glucose-6-phosphate.

The Lactic Acid pathway
The degradation or breaking down of a glucose molecule to liberate energy is known as
glycolysis
, and since the initial stages of the process are performed in the absence of oxygen, it has become technically known as
anaerobic glycolysis.


The Lactic Acid pathway
Once glycogen has been converted to glucose-6-phosphate, glycolysis can begin.

(1) Glycolytic enzymes -
Phosphofructo Kinase (PFK)
&
Glycogen Phosphorylate (GP)
- work on breaking down the glucose molecule in a series of reactions (12 in total) in the sarcoplasm of the cells.

(2) Glucose-6-phosphate is downgraded to form pyruvic acid, which in the absence of oxygen is converted to lactic acid, by the enzyme lactate dehydrogenase (LDH).

(3) This process frees sufficient energy to resynthesise three moles of ATP, but this process uses up energy, so a net gain of
2ATP results
;

The Lactic Acid pathway
Features of the system;

The lactic acid system only frees a relatively small amount of energy from the glycogen molecule
(approximately 5%)
, as the lactic acid produced inhibits further glycogen breakdown as it restricts glycolytic enzyme activity.

Lactic acid levels may increase from
1mmol/kg
muscle at rest to
25mmol/kg muscle
during intense exercise.

Although the lactic acid system is used between
10 seconds and 3 minutes,
it peaks in those events lasting about 1 minute. It also comes into play at the end of aerobic events when the intensity increases, as it does during the sprint finish of a 5,000m race.
The Aerobic system
As the name suggests, this energy system differs from the previous two, as it requires
the presence of oxygen
.

Although it takes approximately
three minutes
to extract the remaining 95% of energy from the glucose molecule, the aerobic system has a tremendous energy yield (
18 x greater
than the anaerobic processes and is therefore worth waiting for!!!
The Aerobic system
The initial stages of the aerobic process are similar to those of the lactic acid system, except that the fate of pyruvic acid changes when oxygen becomes available.
The Aerobic system
Under these aerobic conditions, the glucose molecule is broken down further in special powerhouses or factories existing in the muscle cell, known as the
mitochondria
.

These lie adjacent to the myofibrils and exist throughout the
sarcoplasm
.

Slow twitch muscle fibres possess greater number of mitochondria than fast twitch muscle fibres, which enables them to provide a continuous supply of energy over a longer period of time.
Fact!!!
Under anaerobic conditions pyruvic acid changes to lactic acid which has a fatiguing effect upon the muscles.
In the presence of
oxygen
during light or low intensity exercise, however pyruvic acid is coverted into a compound called
acetyl-coenzyme -A,
which is combined with oxaloacetic acid to form citric acid before it enters the Krebs cycle.
The Aerobic system
The total downgrading of one molecule of glycogen can provide enough energy to resynthesis 38ATP.

2 during anaerobic glycolysis
2 during the Krebs cycle
34 during the electron transport system.


Because of the vast energy supply gained through aerobic metabolism, this system is mainly used in the
endurance based activities
where energy is required over a long period, as well as supplying the energy required by the body at rest, or while it is recovering from any exercise.
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