1.1c energy for exercise

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energy is the capacity to perform work and can exist in chemical, potential and kinetic forms. chemical energy held in the food we eat can be stored as potential energy in the body tissues and converted into kinetic energy as we contract our muscles. maximising this process is essential to improve training and performance
adenosine triphosphate (ATP)
a high energy compound which is the only immediately available source of energy available source of energy for muscular contraction
metabolism
the chemical processes that occur within a cell to maintain life. some substances are broken down to provide energy while others are resynthesised to store energy
ATP breakdown
for the exercising body, ATP is stored in the muscle cell and is the only immediately available source of energy for muscular contraction. it is made up of one adenosine and three phosphates held together by bonds of chemical energy. to extract the energy from ATP, the enzyme ATPase is released, which stimulates the final high energy bond to be broken. this exothermic reaction releases energy for muscular contraction and leaves adenosine diphosphate (ADP) and a single phosphate (P)
ATPase
an enzyme which catalyses the breakdown of ATP
exothermic reaction
a chemical reaction which releases energy
adenosine diphosphate (ADP)
a compound formed by the removal of a phosphate bond from ATP (ATP --> ADP + P + energy)
ATP resynthesis
the store of ATP in the muscle cell is exhausted quickly, lasting only 2-3 seconds: several powerful contractions or several seconds of sprinting. in order to continue exercising, ATP must be constantly resynthesised or rebuilt. to do this, and endothermic reaction occurs where energy from the surrounding area is absorbed to rebuild the high energy bond between ADP and a single phosphate (P). the energy required is provided by one of three energy systems which break down food fuels stored around the body
endothermic reaction
a chemical reaction which absorbs energy
energy systems
there are three energy systems which break down food fuels to provide the energy for ATP resynthesis
ATP-PC
glycolytic
aerobic
at any one time, depending on the intensity and duration of the activity, one energy system will dominate to maintain ATP resynthesis. ATP will then be continuously broken down to provide energy for muscular contraction for the duration of the activity. if ATP fails to be resynthesised, there will be no energy released for muscular contraction and fatigue will quickly set in
the ATP-PC system
the ATP-PC system resynthesises ATP from the breakdown of phosphocreatine (PC) by creatine kinase in a coupled reaction
PC --> C + P + energy in an anaerobic reaction in the sarcoplasm yielding one mole of ATP, for very high intensity activities lasting 2-10 seconds
creatine kinase
an enzyme which catalyses the breakdown of phosphocreatine (PC)
anaerobic
without the presence of oxygen
sarcoplasm
the cytoplasm or fluid within the muscle cell which holds stores of PC, glycogen and myoglobin
coupled reaction
where the products of one reaction are used in another reaction
an example of an activity which uses the ATP-PC system is throwing a javelin in athletics
AO3: ATP-PC system
strengths
no delay for oxygen
PC readily available in the muscle cell
simple and rapid breakdown of PC and resynthesis of ATP
provides energy for very high intensity activities
no fatiguing by products and simple compounds aid fast recovery
weaknesses
low ATP yield and small PC stores lead to rapid fatigue after 8-10 seconds
the glycolytic system
the glycolytic energy system resynthesises ATP from the breakdown of glycogen by GPP and glucose by PFK
glucose --> pyruvic acid + energy in the sarcoplasm yielding two moles of ATP, for high intensity activities lasting 10 seconds to three minutes
pyruvic acid --> lactic acid by LDH due to anaerobic conditions which accumulates to reach OBLA, causing fatigue
phosphofructokinase (PFK)  
an enzyme which catalyses the breakdown of glucose (glycolysis)
anaerobic glycolysis
the partial breakdown of glucose into pyruvic acid
lactate dehydrogenase (LDH)
an enzyme which catalyses the conversion of pyruvic acid into lactic acid
AO3: glycolytic system
strengths
no delay for oxygen and large fuel stores in the liver, muscles and blood stream
relatively fast fuel breakdown for ATP resynthesis
provides energy for high intensity activities for up to three minutes
lactic acid can be recycled into fuel for further energy production
weaknesses
fatiguing by product lactic acid reduces pH and enzyme activity
relatively low ATP yield (1:2) and recovery can be long
aerobic system
the aerobic system kicks in during low to moderate intensity activity as the arrival of sufficient oxygen enables continued energy production. the aerobic system contains three stages:
aerobic glycolysis
kreb's cycle
electron transport chain (ETC)
aerobic glycolysis
aerobic glycolysis in the sarcoplasm converts glucose into pyruvic acid with the enzyme PFK catalysing the reaction. this releases enough energy to resynthesise 2 molecules of ATP. converting glycogen into glucose (by enzyme GPP) maintains process for extended periods of time. as oxygen is now in sufficient supply the pyruvic acid is no longer converted into lactic acid. it goes through a link reaction catalysed by coenzyme A, which produces acetyl CoA. this allows access to the mitochondria.
Kreb's cycle
Acetyl CoA combines with oxaloacetic acid to form citric acid, which is oxidised through a cycle of reactions. known as the kreb's cycle, CO2, hydrogen and enough energy to resynthesise two molecules of ATP are released. this process occurs in the matrix (intracellular fluid) of the mitochondria
electron transport chain (ETC)
the hydrogen atoms are carried through the ETC along the cristae (folds of the inner membrane) of the mitochondria by NAD and FAD (hydrogen carriers), splitting into ions (H+) and electrons (H-). hydrogen ions are oxidised and removed as H2O. pairs of hyrogen electrons carried by NAD release enough energy to resynthesise 30 moles of ATP and those carried by FAD release enough to resynthesise 4 moles of ATP. the overall yield of the ETC is 34 moles of ATP
an example of an activity that uses the glycolytic energy system is a 200m sprint
an example of an activity that uses the aerobic energy system is a marathon
lipase
an enzyme which catalyses the breakdown of triglycerides into free fatty acids (FFAs) and glycerol
AO3: aerobic system 
strengths
large fuel stores: triglycerides, FFAs, glycogen and glucose
high ATP yield and long duration of energy production
no fatiguing by products
weaknesses
delay for oxygen delivery and complex series of reactions
slow energy production limits activity to sub-maximal intensity
triglycerides or FFAs demand around 15 per cent more O2 for breakdown
energy continuum
the relative contribution of each energy system to overall energy production depending on intensity and duration of the activity
intensity very high: duration <10 seconds
in individual activities such as athletic jumps, throws and sprints, where the intensity is very high and duration is 2-10 seconds, the ATP-PC system will be predominant, contributing up to 99 percent of energy for ATP resynthesis
intensity high: duration 10 seconds to 3 minutes
in individual activities such as the 400m, 200m freestyle ad a competitive squash game where the intensity is high and duration is between ten seconds and three minutes, the glycolytic system will be predominant, contributing 60-90 per cent of the energy for ATP resynthesis
intensity low to moderate: duration >3 minutes
in individual activities such as marathons, triathlons and skiing, where the intensity is moderate but relatively constant for a significant duration, the aerobic energy system will be predominant, contributing up to 99 per cent of energy for ATP resynthesis
intermittent exercise
where the activities intensity alternates, either during interval training between work and relief intervals or during a game with breaks of play or changes in intensity. e.g., a rugby player is required to alternate between various modes of activity such as standing, walking , sprinting, tackling and jumping. performing intermittent exercise is more energy demanding than continuous exercise when the running speed is the same, which places games players in a unique situation, with varying physiological demands as they switch from one energy system predominance to another
threshold
the point at which an athlete's predominant energy production moves from one energy system to another
ATP-PC / glycolytic threshold
as a wing attack in netball hears the whistle, they will sprint out to receive the centre pass over 3-4 seconds using the ATP-PC system. however, losing possession leads them to man-man mark for a period of time of up to one minute to regain possession. the PC stores quickly deplete and the glycolytic system takes over predominant energy production
glycolytic / aerobic threshold
after the counter attack in netball results in a goal being scored, the player jogs back into position ready for the next centre to be taken . the intensity is significantly reduced and there is sufficient oxygen available for the aerobic system to take over to provide most of the energy for ATP resynthesis
additional factors which will affect the relative contribution of energy systems to overall energy production, for a games player
position of the player: for example, a goalkeepers aerobic energy system may be predominant with a small percentage from the ATP-PC system for very high intensity dives, kicks and defensive plays, whereas a central midfielders aerobic system will be required to jog back into position and track play, their glycolytic system will be used for counter attacks and set pieces and the ATP-PC system for high intensity shots or tackles
additional factors which will affect the relative contribution of energy systems to overall energy production, for a games player
tactics and strategies used: for example, man-man marking will raise the intensity compared with zonal marking and will require a larger contribution from the anaerobic energy systems