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WRM0200 RevB
Muscular fitness is a combination of strength, endurance and flexibility. Resistance training occurs over a
short time frame and does not necessarily improve endurance capacity or for that matter flexibility. There
may even be a decrease in endurance capacity because as the muscle cells grow the fluid between the cells,
essential to oxygen transportation, is reduced.
There is also evidence to show that resistance training can cause an increase in blood pressure.
AEROBIC BASED EXERCISE
Aerobic training relates to the processes by which the body generates the energy to perform work. The principal
fuels used to produce energy are the body’s stores of fat, carbohydrate or protein. These fuels can be converted
into energy by one of two processes, the aerobic metabolic process or the anaerobic metabolic process.
The aerobic process consumes fuel in the presence of oxygen (supplied by the flow of blood) producing
by-products, carbon dioxide and water, which are expelled by espiration and perspiration. The aerobic process
provides the majority of the energy used by the slow acting muscle fibers (crucial to endurance activities).
The Anaerobic process occurs when there is not enough oxygen in the blood to produce energy aerobically. This
process consumes carbohydrate as its primary source of fuel and does so in the absence of oxygen, producing
a by-product called lactate. It is lactate which produces the muscle soreness and fatigue associated with
excessive exercise. The anaerobic process provides the majority of the energy used by the fast-acting muscle
fibres (crucial to strength and power activities).
When we start exercising, energy is initially produced anaerobically until the respiratory and cardiovascular
systems respond and supply the oxygen necessary for aerobic energy production, hence the increase in
breathing and heart rates. Once oxygen supply is sufficient, most of the energy will be produced aerobically,
with the balance supplemented anaerobically. The lactate formed by this residual anaerobic production is
easily dissipated by the body’s organs, avoiding any onset of fatigue.
As exercise intensity increases the muscles’ ability to produce energy aerobically will reach a limit (defined
by the capacity of the respiratory and cardiovascular systems to supply additional oxygen). At this point the
body cannot supply additional oxygen, and energy production becomes anaerobic. This transition point is the
maximal aerobic output and is called the aerobic threshold. Exercise above this level causes a rapid build-up
of lactate, leading to muscle fatigue which will cause cessation of exercise.
Knowledge of the aerobic/anaerobic process is essential to the successful attainment of specific exercise aims.
Fat burn (weight maintenance), cardio-vascular training (cardio-vascular or endurance fitness) and anaerobic
training (tolerance to fatigue) all rely on an understanding of the way our body produces energy.
WEIGHT MAINTENANCE
At lower intensities our body uses a mixture of fat and carbohydrate as its source of fuel. As the maximum
aerobic output is approached, the percentage of fat consumed as fuel reduces to zero. Also, as the duration of
exercise is increased the percentage of fat consumed tends to increase.
If your objective is weight maintenance, then it is necessary to burn as much fat (as opposed to carbohydrate)
as the source of fuel as possible. This is best achieved at lower intensities and over longer durations. As soon
as the intensity is increased the aerobic process starts to burn more carbohydrate and the weight maintenance
effect will be reduced. A low intensity (60 - 70% of the maximal aerobic output) is typically that at which you can
hold a conversation: it is by no means strenuous and is about that achieved by a brisk walk.
AEROBIC TRAINING
A sustained exercise program will improve the efficiency with which the respiratory and cardiovascular system
can supply oxygen. This improves lung function, heart function, vascular efficiency and capillary growth, leading
to improved well being and endurance.
At about 70 - 80% of the maximal aerobic output, lactate begins to accumulate in the blood supply at a greater
rate than it can be extracted by the liver, kidneys and other organs. Exercising above this intensity will cause
progressive accumulation of lactate in the blood, increased heart and breathing rates, cause muscle fatigue
and will eventually lead to the cessation of exercise. Prolonged exercise at or below this intensity will maintain
lactate at non-fatiguing levels and exercise duration will be limited solely to the depletion of available fuel
stores.
If your exercise objective is aerobic (cardio-vascular/endurance) training then it is necessary to exercise at an
intensity which will avoid fatigue due to lactate build up. This is best achieved at moderate levels of intensity
over medium/long durations.
A moderate exercise intensity (70 - 80% of the maximal aerobic output) is about that achieved by a steady jog,
avoiding the onset of muscle soreness.
