Energy systems and how to train them
The three metabolic energy systems operating in our bodies provide the energy we need to contract muscles. These energy systems operate continuously and it is how long and how hard we do whatever physical activity that determines which system contributes most. The three energy systems are:
1. The Aerobic System - The muscle energy system which requires oxygen
2. The Lactate System - The ‘linking’ energy system which is capable of operating without oxygen and produces lactate and acid
3. The Alactic System - The stored, start-up energy system which is capable of operating without oxygen but does not produce lactate or acid.
Although these three energy systems are distinct, they actually work together continuously to provide the energy needed for movement. There is no ‘switch’ inside of our bodies that suddenly says, “O.K., now you’re going to switch to the aerobic system.” Or, “Now, you’re going to switch to the lactate system or to the alactic system.” The following diagram illustrates the contribution of the three energy systems over time, assuming that the runner is trying to perform at their optimal intensity for the duration of the activity. The word ‘optimal’, in this use, means the most intense pace that the runner can maintain for the duration of the activity. You will see that the ‘Time arrow’ is not continuous but broken at 10 seconds and approximately 3 minutes so that the important changes in emphasis can be more clearly shown.
The aerobic-anaerobic split refers to how much the aerobic and anaerobic energy systems are emphasised in a particular activity. Distance runners produce most of their energy aerobically and with the lactate system but we still need to train the a-lactic system for those times when your runner wants to sprint to the line and to develop leg turnover.
| System | |||||
|---|---|---|---|---|---|
| AEROBIC | Uses oxygen and fuel stores to provide energy | Prolonged low to moderate intensity work | Aerobic endurance training, e.g. steady state running, cycling, swimming for 20-30 minutes or longer | Improved transportation of oxygen to the working muscle, use of fuels and removal of waste products | Heart rate below 80% of max depending on fitness |
| LACTATE | Capable of operating when oxygen is present or absent but produces lactate and acid | The ‘linking’ energy system that can provide energy over the complete range of durations and intensities | Repetition training, fartlek and circuits where higher intensity work is required with partial recovery during short lower intensity periods | Improved ability to generate energy from this system and to create and use lactate as an aerobic fuel source | Heart rate – 80 – 90% of max depending on fitness |
| ALACTIC | Capable of operating when oxygen is absent and no lactate or acid produced | Immediate high intensity activity but can only sustain it for a few seconds | High quality speed and power work (2-8 secs.) with enough rest to allow full recovery and replenishment of the CP | Improved ability to perform maximal efforts and a greater capacity to produce such efforts repeatedly |
*Heart rate zones are different for different runners. Generally speaking, a runner who has been training for longer, will be able to operate longer within training zones at a higher heart rate as their heart muscle has been trained to become more efficient. To calculate percentages of maximum heart rate, use the formula below:
Maximum heart rate = approximately 220 minus your age. This is a rough estimate.
Subtract your resting heart rate (should be taken on waking up)
Calculate the percentage of this number and then add the resting heart rate back on.
Eg, Joe is 40 years old with a resting heart rate of 60.
You want Joe to run some efforts at 90%.
· 220 - 40 = 180
· 180 - 60 = 120
· 90% of 120 = 108
· 108 + 60 = 168
· 168 - pace for anaerobic sessions.
Aerobic energy – the endurance energy system
The aerobic system requires oxygen. This system is emphasised in lower intensity exercise and is the basic system which provides the energy for most human activity from birth to death. As such it is also important in recovery from exercise of all intensities. It is very efficient and does not produce waste products. The heart and lungs are important in aerobic activity as oxygen and fuel are carried to the muscles in the blood.
The aerobic system resists fatigue. It takes longer to overload than either of the other two energy systems. To train the aerobic energy system a minimum of 20 minutes duration of activity must take place and the heart rate will be less than 80% of maximum. The work load for aerobic training can be either continuous or broken up into repetitions of harder and easier running or exercise. Correct aerobic training will improve aerobic energy production in the muscle and also improve the efficiency and function of the heart and lungs, the oxygen transport system.
Training sessions include easy runs and steady runs where the heart rate stays below 80% of max.
Lactate energy system – the ‘linking’ energy system
The lactate energy system is called the ‘linking’ system because it provides the bridge between the capabilities of the aerobic and alactic systems. Lactic acid forms when the exercise is intense. Before we really understood the energy systems, lactic acid was seen as a waste product that would slow runners down but we now know that lactic acid or part of it, can help us produce more energy, more quickly. As soon as it is formed it splits up, separates, into a ‘lactate bit’ and an ‘acidic bit’. The lactate bit is definitely not a ‘bad guy’ but is instead is a ‘good guy’ playing a positive and central role in our metabolism and in how we produce energy.
Understanding this role of lactate in the body is important and can be applied to produce major improvements in runners’ performances. The lactate system is capable of operating without oxygen but is operating all the time, like all of the three energy systems. This energy system is more emphasised in exercise of high levels of intensity but this high intensity may prevent the removal of the lactate and acid bits if not enough oxygen is available. When it does operate without sufficient oxygen, the lactate and acid accumulate within muscle cells and the blood.
The lactate is a useful source of fuel for the runner and correct training helps the body both use and clear lactate but the acid is a major cause of fatigue, which eventually slows the runner. As you are sitting and reading this you are producing lactate and acid and, at the same time, you are using it and moving it around the body but you are not building up high levels of the acidic bit and so you are not aware of the process. Lactate production within your muscles occurs in healthy, well oxygenated individuals at all times.
Leaders and runners, however, are not so much concerned with rest as to what happens during exercise and in the recovery from exercise.
It may take more than one hour for lactate and acid levels to return to their pre-exercise level. Recovery activities such as walking, easy running or more active running following intense efforts will speed up the removal of the acid. The first ten minutes of active recovery produces the greatest reduction in lactate and acid levels.
The lactate energy system may be developed by continuous activities or varying the intensity of repetition of work loads of 10 seconds to almost any duration. Rest periods and recovery activity will depend on the duration of the work and should be thirty seconds to ten minutes to allow utilisation of the lactate and removal of most of the acid that is produced. Training sessions include fartlek training, progression runs, repetitions and interval work.
Alactic Energy System – the ‘First 10 seconds’ energy
The alactic system is the one referred to as the ‘stored’ or ‘start-up’ energy system. This system provides the majority of energy when our runners do bursts of high speed or high resistance movements lasting up to 10 seconds. The stores of energy, Creatine Phosphate (CP), in the muscle which are used up in the intense burst of activity return to normal levels within 2-3 minutes of rest.
The alactic energy system is developed by alternating periods of exercise and rest. The work time should be very intense, usually of 2-8 seconds and should not exceed 10 seconds, as this is the limit of the energy system. The rest periods should be 2 to 3 minutes, depending on the duration of intense activity, to allow the muscle energy, CP, stores to build up again. If a runner shows the effects of fatigue, allow more rest time or decrease the work time.
Summary of the Development of the Three Energy Systems
| ALACTIC | LACTATE | AEROBIC | |
|---|---|---|---|
| Duration | 0-10 secs | 10 secs-1+ min | 1-60+ mins |
| Distance | 20m-80m | 80m-400m | 300m-15+ km or Continuous |
| Intensity Maximal | 80%-100% | 50%-80% | |
| Repetitions | 3-4 | 1-5 | 3-20+ |
| Recovery/Reps | 2-3 mins | 30 secs-10 mins | 30 secs-3 mins |
| Sets | 1-4 | 1-4 | 1-4 |
| Recovery/Sets | 5-8 mins | 5-20 mins | 5-8 mins |
In summary, all three energy systems work continuously:
• the relative contribution of energy from each energy system to a particular physical activity will depend on the energy requirements, which will be directly related to the intensity and duration of the exercise
• different events have different types and amounts of activity
• different events therefore emphasise different energy systems.
Questions that may have arisen from this article:
· How much training should my runners do in each of the energy systems?
· Can you give me more specific examples of training sessions that would train these systems?
· Does a training session need to focus on just one energy system or could I plan a session that uses two or even three of them?
See this article (INSERT LINK) for how to plan a variety of sessions that will give your runners the right amount and type of training aerobically and anaerobically.