The energy continuum
The energy continuum is the interaction of the 3 energy systems to
provide energy to resynthesise ATP. It shows the predominant
system or percentage of each system dependant on the intensity and
duration of the activity.
At the beginning of exercise all 3 energy systemsstart.
The dominant system initially is the ATP/PC as shown on the
diagram. As the PC is exhausted (ATP-PC/lactic acid threshold) the
lactic acid system takes over. Depending on the intensity of the
activity, the lactic acid/aerobic threshold is reached between 1-3
mins. The aerobic system now becomes the main provider of energy
for ATP resynthesis.
The diagram does not show the initial depletion of ATP – so the
energy systems begin after approx 2-3 secs. This is shown on the
next diagram.
Onset of blood lactate accumulation (OBLA)
During higher intensity activity lactate levels rise. Blood lactate
levels at rest and during aerobic activity (remember during aerobic
activity lactic acid is not produced) is aprox 2mmol/L(2 millimoles
per L of blood). When blood lactate begins to rise during anaerobic
activity and lactate levels reach 4 mmol/L, it is said to be the onset
of blood lactate accumulation – OBLA.
If the activity intensity continues or increases OBLA will continue to
rise. The result of this is:
- Lower blood pH (increased blood acidity)
- Inhibition of enzyme action
- Pain receptors stimulated
- Muscle fatigue/pain
- Reduction in performance
This diagram adds a little more detail – Initial ATP
depletion/thresholds. The shape of the line representing the lactic
acid system in particular will change depending on the intensity of
the activity – so, therefore will the threshold where the aerobic
system will take over as the predominant system for ATP
resynthesis. This explains the small difference between the two
diagrams.
Key points to learn related to the diagram:
-Start points of each system
-Shape of each system (relate to the timings/duration of each
system)
-Time of the thresholds – ATP-PC/lactic acid and lactic
acid/aerobic.
Remember the thresholds are the point where the one energy
system takes over as the predominant (main supplier) energy
supplier, not the point at which the energy system stops. This point
will show good understanding and get a mark within an exam.
Fitness levels - can change the thresholds.
An aerobic athlete will have a more efficient cardiovascular and
respiratory systems. They will have a greater ability to transport
and use O2 to breakdown glycogen and FFAs (aerobically) to
resynthesise ATP.
Aerobic athletes will be able to work at higher intensities before
their lactate threshold and OBLA will be reached.
Aerobic athletes will reach OBLA at approx 85-90% of their VO2
max (compared to 50-55% for average person)
An anaerobically trained athlete can also delay the ATP-PC/lactic
acid threshold by increasing :
ATP/PC/glycogen stores.
Increased anaerobic enzymes (creatinekinase/ GPP/PFK)
Increased tolerance of lactic acid.
Team sports require the 3 systems to be used at different times.
You need to be able to explain where each system is used within the
game. Be specific in terms of time and intensity as well as the
description of the movements. This is a popular exam Q!
Possible exam Q-Factors affecting energy system used:
Test your knowledge – use following key words – add details to
each point. (revision book p168-171)
1 Intensity and duration of exercise.
2 Fitness level :
- OBLA
- Energy system thresholds
- O2 availability
- Enzyme activity
- Fuel availability