For the purposes of my book and my lecture series, I’ve described Arthur Lydiard’s work as progressively moving up and down a pyramid of training intensities and levels, until the hardest and most intense work is done before the most important competition. This approach is now common to all sports with an endurance component, and is known as periodization.
There are three main energy systems in the body…
There are three main energy systems in the body, and they largely correlate with three different time frames, three different muscle types, and three different main fuels. In exercise physiology, there is no standardisation of terms for the different energy systems, and there are several different sub-classes of muscle fibre types, which may be intermediary, however we’ll keep things as simple as necessary to outline the main points.
There are TWO Anaerobic systems in the body…
There are TWO Anaerobic systems in the body, entirely different to each other. The first type runs for only a few seconds off intramuscular fuel, and does not produce acidic by-products. It is the ALACTIC ANAEROBIC SYSTEM, and correlates with the largest and most powerful fast twitch fibers, the IIB.
The second of the two anaerobic systems, the LACTIC ANAEROBIC SYSTEM, only comes into play after the alactic system winds down. It depends on the breakdown of glucose for energy without oxygen, and this produces a lot of acid in the muscles as a by-product of the formation of lactate. The IIA fibers can acquire aerobic characteristics with long-term endurance training, and acquire a dense population of mitochondria to metabolize fatty acids as well as glucose.
The third energy system is the AEROBIC system
The third energy system is the AEROBIC system, and it correlates most with the small, fatigue-resistant Type I slow-twitch muscle fibers. These fibers are loaded with myoglobin, which is a red protein within the muscles that is almost identical to the haemoglobin in the red blood cells. Both proteins have a huge affinity for oxygen and carbon dioxide transfer from aerobic respiration.This system responds extremely well to lower intensity training well below the anaerobic threshold, and has the capacity to increase its mitochondrial density and oxidative enzyme capacity immensely. It has the capacity to burn up fats and glucose within the energy furnaces of the cells, the mitochondria, and in terms of efficiency is many times better than the anaerobic systems in its energy yield.Fats can be recycled many times over to produce energy by a process known as beta-oxidation. We’ll talk later on about fat-adapted training for endurance runners, and the difference between being a sugar-burner or a fat-burner when running aerobically.
The three different energy systems in the body take differing times to grow to their fullest capacity. The slowest to develop to full capacity is the aerobic energy system, which can be constantly improved for many years. This is because many years of steady endurance training well within our comfort zones encourage the formation of very deep capillary beds deep into the muscle beds of the legs and also the body’s most important slow twitch muscle; the heart itself.
Several months of longer duration steady training within our comfort zones will result in a marked increase in mitochondria (energy furnaces) within the muscles, particularly in the slow twitch type I muscle fibers, and over time, similar ‘oxidative’ changes start to occur in the IIA fast twitch muscle fibers, allowing them to acquire aerobic qualities, with enzyme systems and mitochondrial populations that will support aerobic use of glucose in a similar fashion to the slow twitch fibers. The trouble is that this glucose, or the chains of stored glucose called glycogen, has limited accessible storage in the body; at most around 2 hours’ worth before the stores run out and the muscles have to slow down their rate of work
The fastest system to develop to maximum tolerance is the glycolytic anaerobic energy system, otherwise known as the lactic acid system, at the top of the pyramid, which can reach its highest capacity in a number of weeks if a suitable aerobic foundation has been laid. We only train this system with great control and care, after we have carefully built and progressed fitness through the ascending aerobic stratas. Due to the acidosis it invokes, intense glycolytic anaerobic training has to be done in a very tightly controlled way because it invokes so much systemic acidosis, which is deleterious to general health and immunity if done too much.
The alactic anaerobic energy system, which contributes less and less to overall performance as distance increases, can be developed very quickly too. However, while alactic capacity at the chemical level in the cells can be pushed up to its maximum quickly, the neuro-muscular coordination to run fast when relaxed is a skill that has to be learnt and reinforced over time. The skill is in the exact timing of the relaxation phase between powerful hamstring muscle contractions which results in the ‘taking the brakes off’ fluidity of much faster leg turnover.This is well-explained in my book, Healthy Intelligent Training, and the lecture series.
The efficient movement patterns learnt with fast alactic running can contribute to efficiency at all speeds. The difference between absolute maximal speed and race pace eventually becomes a comfort zone. So although the overall energy contribution of the alactic system is minimal for the duration of a middle distance or distance race, alactic training is very important year-round because of its effect on efficiency and economy, and also because many races come down to a sprint at the end.
This type of work can be done safely on a year-round basis, especially on easy days, and doing so will not harm the aerobic systems, especially if plenty of easy recovery running is done between short, fast, relaxed efforts.Whatever the IIB muscle fibres with their super high-energy alactic creatine phosphate system can churn out in 6 to ten seconds of relaxed fast sprinting will be at a much higher work rate than the fastest speeds that can be maintained by the second-order fast twitch fibres, the IIA fast twitch glycolytic muscle fibres. THE IIA fibres don’t primarily access high-energy creatine phosphate as a fuel source, but will access energy from the slightly slower-working glycolytic system that breaks glucose down into energy. Glycolysis, the breaking down of a six-carbon glucose molecule into two three-carbon molecules, starts in the cell fluid or cytoplasm of the muscle cell, and if there is enough oxygen, aerobic glycolysis proceeds further within the mitochondrion, an organelle with a double-membrane that is able to continue stripping two three-carbon molecules down into thee two-carbon molecules called acetyl CoA, with a nett production of energy released from the breaking of high-energy phosphate bonds, plus carbon dioxide and water.
If there is insufficient oxygen diffused into the cytosol of the muscle cell, then anaerobic glycolysis stops right there with a relatively small release of energy from phosphate bonds, and resulting only in two three-carbon products called lactic acid, which accumulates in the cytoplasm, stopping normal muscle recruitment and contraction before it can really continue.Anaerobic glycolysis of a 6-carbon glucose molecule will yield only two high-energy adenosine triphosphate molecules and two molecules of lactic acid. If aerobic glycolysis of the same glucose is allowed to continue in the mitochondrion, this will yield another 34 molecules of ATP, making a total of 36 ATP high-energy molecules produced in the aerobic process compared to the lowly 2 molecules of ATP in the anaerobic glycolysis process. The difference in energy output is 18 times more favourable with aerobic exercise. However, glycolysis is using a limited fuel, whether it is aerobic or anaerobic, and furnishes nothing like the amount of ATP energy that lipolysis can yield. A typical human fatty acid like palmitic acid is a string of 16 carbon atoms bonded to two hydrogens each.Each one of those H–C–H units undergoes what is known as beta-oxidation, with the 16-carbon fat molecule eventually furnishing 129 molecules of ATP: 3.58 times more nett energy per molecule.
So it can be seen that the training pyramid concentrates on different energy systems at different times, in a balanced way that ensures all of them come up to the maximal capacity possible at just the right time.
One type of work leads progressively into another. It must be remembered that aerobic work of an easy or extremely easy nature can be continued in reasonable volume right into the race phase.
In fact, if intense work is being done at the top of the training pyramid, it must be assumed that it is being buffered by ample very low intensity running sessions that are very aerobic in nature. This balances the system and allows the body to cope with the mounting acidosis that hard training and racing invokes, and come back for more intense training again.