Energy for Exercise by James Wingfield and Jon Folland

There are 3 major energy pathways in the human body, known as the aerobic, anaerobic and ATP/PC pathways. They can and often do work simultaneously, but the demand on each depends on the intensity and duration of exercise.

To understand the use of the energy systems it helps to consider, if you start paddling slowly, and then progressively increase pace for 15 minutes until you are doing a maximum sprint, which can only be maintained for a few seconds.

In the first few minutes all the energy is produced by the aerobic pathway, that is energy produced 'with oxygen'. As the pace goes up clearly more energy is required, we start to breathe more heavily and this extra energy comes from greater use of the aerobic pathway. As the pace goes up again, more and more energy is demanded of the aerobic energy pathway, however it can only supply energy at a maximum rate, and when we reach a pace that could only be maintained for about 8 minutes then the aerobic pathway is working at maximum.

Further increases in pace are possible but the additional energy is supplied by the anaerobic pathway, that is energy produced 'without oxygen'. However, this energy pathway has some nasty side effects, notably lactic acid is given off and causes fatigue. If the pace goes up again it requires more anaerobic energy, and thus quicker build up of lactic acid and increasingly intense fatigue.

Finally if the paddler sprints all out the extra energy for this really high intensity work comes from ATP and PC, which are small very short-term stores of energy in the muscle.

(N.B. The aerobic pathway will continue supplying energy at its maximum rate right to the end of the sprint, its just that it cannot supply all the energy demanded, and other pathways must contribute at these high speeds.)

Training the Energy Pathways

Training for the 3 energy pathways will be considered below. The energy pathways involved in an event represent just one part of the myriad factors important for physical training and competition. The period of training given is just an indication to achieve a reasonable level of fitness for each. Of course we can (and some people do!) spend a lifetime continually trying to improve each of these qualities.

1. The aerobic system also known as the O2 system.
Aerobic means "with oxygen", this pathway is used when sufficient oxygen is available to meet the energy needs. In this case the fuels fatty acids and glycogen are metabolised with oxygen to provide the energy (ATP) for muscle contraction. Typically the aerobic pathway is used for long periods of low to medium intensity. This is the endurance system and you can use it almost indefinitely. A marathon runner trains and races at a relatively low intensity (I know they go fast, but that's just because they are very fit!) all the energy for their exercise will be produced by the aerobic pathway. It is the most efficient of the three systems for converting fuel into energy.

During easy exercise this system will also dissipate any lactic acid built up in the muscles from higher intensity bouts using the anaerobic energy system.

It takes 3 to 4 months of steady training to develop aerobic fitness. To improve aerobic fitness it takes 3 to 6 sessions per week and to maintain existing aerobic fitness it takes 2 to 3 sessions per week. You should also include 1 speed session per week to keep up some speed.

There are 3 main ways to develop aerobic fitness:

(a) Training sessions that are a minimum of 45 minutes of steady-paced effort and preferably over an hour. During these sessions the intensity should not be tiring, but it is the duration that leads to fatigue. This training is primarily for the aerobic ability of the muscles, and you should be able to talk to people while doing this type of training, not be gasping for breath. This type of training is particularly good for general fitness, health and weight loss without being too hard.
(b) Repeated hard efforts of between 3-6 minutes. These sessions develop the maximum rate of the aerobic system. As they are hard efforts there will be some anaerobic metabolism, but this is required to work the heart and lungs to a high level. At the end of these efforts you will be breathing very hard and it may take a minute or so for this to come back to normal.
(c) Threshold training 20-40 minutes of hard effort, where the pace is very close to maximum for the distance. This trains the aerobic system just at the point where noticeable amounts of anaerobic energy are produced, and thus the aerobic pathway adapts to working well even if there is some lactic acid and fatigue. During this type of training you will be breathing quite hard, but if you stopped your breathing would come down to normal quickly.

2. The anaerobic pathway

Used for limited periods of fairly high intensity effort. It is the major energy pathway for events lasting from 10 to 90 s. For sports events of this duration the intensity is too high for purely the aerobic pathway (which can only supply energy at limited rate) and most of the energy comes from the anaerobic pathway, which involves the metabolism of glycogen "without oxygen". This reaction has a by- product of lactic acid, which causes fatigue - basically the intense burning sensation and failure of muscle contraction at the end of a 400 m running race as the legs turn to jelly. The higher the rate of energy supply from this anaerobic pathway the faster the build up of lactic acid and the quicker the onset of fatigue.

This energy system is most important for long sprints (10 -90 s), but also important for middle distance events (90 - 360 s).

The ability of muscles to work with lactic acid build up and the consequent fatigue can be trained using interval training, typically reapeated efforts of 30 seconds to 2 minute.

It takes 6 to 8 weeks of training to develop the anaerobic system. To improve fitness it takes 2 to 4 sessions per week and to maintain existing fitness it takes 1 to 2 sessions per week.

You normally start to train the anaerobic system about 8 weeks before the event, and between 6 and 2 weeks prior to the event your training should be at its most intense. It is important to maintain your aerobic fitness as well.

A typical anaerobic session would be:
(2 min on, 2 min off) * 10
10, 20,-----90, 100, 90,------20, 10 stroke pyramid
{(40 on, 20 off) *3, (80 on, 40 off) *3, (40 on, 20 off) *3} *3

3. The ATP/PC pathway

Used for very short periods of maximum intensity effort. ATP (Adenosine triphosphate) and PC (phospho-creatine) are energy stores in the muscles that last for less than 10 seconds of all-out maximum sprinting. It takes ~2 min of rest or easy work befor these stores are replenished. This is the main energy pathway for a 60-m running sprint (<7s). This energy pathway does not require oxygen or produce any nasty by-products. This energy system is most important for very short sprints (<10 s), but also medium sprints (10 - 30 s).

Training is thought to increase the rate of energy supply from ATP-PC (i.e. faster maximum speed and extend the time it lasts for by a few seconds.
.
This system can be trained up in 3-4 weeks and is lost in a similar time, so tends to be trained in the month before the event.

A typical ATP/CP session would be:
10 second effort every 2 minutes *20
10 second sprints during a long steady paddle
practising starts from standstill

NB When planning training schedules, try to spread the types of training out. If you have a hard interval session one day, have a steady aerobic session the next day etc. Remember, training alone doesn't improve preformance, it is training plus adequate recovery that improves performance.

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