Endurance Training
Triathlon is often described as an Endurance sport, what does this mean?
Whatever movements we are undertaking we need to consider the amount of force we are generating, the speed of the movement and how long we need to sustain them for. The force and speed of the movements come together to generate power/work. The amount of time we can sustain them for is a measure of endurance. So what we mean by endurance needs to be consider in terms of the events we are participating in. So for example when aiming to complete a marathon in under 3:00 having sufficient endurance would mean being able to average 14+ km/h for the duration of the race. However if you are competing in a 400m on the track and aiming to complete the race in under 50 secs having sufficient endurance would mean averaging 29km/h. If in either event holding the required pace for even a short time was a challenge then speed or strength may be a limiter, however not being able to hold the desired pace for the duration of the event would show a lack of endurance. So endurance can be a factor in both long and short events.
When people use the term 'Endurance sport' it might be more accurate to swap the term endurance for aerobic as they are usually refering to activities that challenge the capacity and/or efficiency of the aerobic energy system.
What do we mean by the Aerobic energy systems?
In order to contract and generate force, skeletal muscle requires the release of energy present in chemical compounds in the muscle. These include:
- Adenosine Triphosphate (ATP)
- Creatine Phosphate (CP)
- Carbohydrates
- Fats
- Proteins
- ATP-CP
- Anaerobic Metabolism
- Aerobic Metabolism
- The rate at which these systems can supply energy is largely determined by the number of chemical reaction (steps) involved in each - ATP-CP is the fastest, followed by anaerobic metabolism and finally aerobic metabolism with an approximate ratio of 4:2:1 in terms of the maximum rate of energy supply.
- The total amount of energy that can be supplied by each system using the available chemical compounds is much larger for aerobic metabolism than Anaerobic metabolism with ATP-CP coming in last.
- The first 2 of these systems don't require oxygen to supply energy. They are therefore referred to as anaerobic meaning without oxygen.
- Aerobic metabolism requires sufficient oxygen in order to be able to function.
Data for swimming:
|
Event (Duration) |
~V02 Max |
% Energy Contribution |
||
|
ATP-CP |
Lactate |
Aerobic |
||
|
25m (0:10-0:15) |
|
50 |
50 |
Neg |
|
50m (0:19-0:30) |
|
20 |
60 |
20 |
|
100m (0:40-0:60) |
|
10 |
55 |
35 |
|
200m (1:30-2:00) |
|
7 |
40 |
53 |
|
400m (4:00-6:00) |
|
/ |
35 |
65 |
|
800m (7:00-10:00) |
|
/ |
25 |
75 |
|
1500m (14:00+) |
|
/ |
15 |
85 |
Data for Running:
|
Event (Duration) |
~V02 Max |
% Energy Contribution |
||
|
ATP-CP |
Lactate |
Aerobic |
||
|
100m (0:10) |
/ |
70 |
22 |
8 |
|
200m (0:20) |
/ |
40 |
46 |
14 |
|
400m (0:45) |
/ |
10 |
60 |
30 |
|
800m (1:45) |
135 |
5 |
38 |
57 |
|
1500m (3:35) |
112 |
2 |
22 |
76 |
|
3000m (7:45) |
102 |
<1 |
12 |
88 |
|
5000m (13:20) |
97 |
<1 |
7 |
93 |
|
10000m (27:50) |
92 |
<1 |
3 |
97 |
|
Marathon (2:10:00) |
82 |
<1 |
<1 |
99 |
Whilst not identical, what this data shows is that the aerobic energy system is the predominant in any event taking upwards of 2:00 with a significant contribution in events as short as 20 seconds. This means that with most triathlon taking upwards of 1:00:00 to complete it can clearly be described as an aerobic sport.
How do I know if my aerobic energy system is any good?
It's tempting to say your aerobic energy system is good if you are good at aerobic sports (how's that for stating the bleeding obvious), however the situation once you start to consider performance is not quite that simple as a few other factors come into play:
- Mechanical efficiency - This is made up of good technique and your anthropometry. Technique is underpinned by sports specific strength / speed / flexibility as well as your ability to learn good movement patterns. Anthropometry is the way your body is put together in terms of weight, height, limb length/breadth/girth some of which you can alter, others you can't. How much your technique and anthropometry limit your performance is dependant upon the demands of the event.
- Motivation - Boredom and pain/discomfort can be factors in performance in aerobic sports depending upon the specific demands of the event.
We'll leave those there for a minute and get back to the question at hand. You can check your aerobic energy system function by undertaking the following types of fitness tests:
- Oxygen Consumption responses to exercise: VO2 Max
- Blood Lactate Responses to exercise: LactateThreshold / Lactate Turnpoint
To understand these tests we need to consider the energy systems in a little more detail:
Test 1: Oxygen Consumption Responses to exercise - VO2 Max
We've already established that aerobic metabolism requires oxygen to function. This oxygen gets into the body in the air we breath which is made up of 78% Nitrogen, 21% Oxygen and 1% made up of other gases (note these % do change depending upon altitude, temperature and pressure). Aerobic metabolism takes the output of anaerobic metabolism (pyruvate and hydrogen ions) and with sufficient oxygen available uses them as inputs to it's processes (Krebs Cycle and the Electron transport chain). Pyruvate is metabolised to Carbon Dioxide (CO2) in Krebs Cycle and Hydrogen Ions are metabolized to water in the electron transport chain. The water can be reused in the body whilst the CO2 is expired in the air we breath out along with any unused oxygen and other gases. By measuring the amount of oxygen in inspired air and comparing it to the amount of oxygen in expired air we can calculate oxygen utilisation for aerobic metabolism in working muscles. Every athlete has a trainable upper limit to their ability to metabolize pyruvate and hydrogen ions related to their ability to take in and utilise oxygen. By undertaking a progressive exercise test and monitoring oxygen utilisation during the test it is possible to identify an athletes VO2 Max (maximum ability to utilise oxygen) and report this either as X L/min or more commonly X ml/kg/min to account for differences in athletes body weight.
The list below gives you an indication of what values you might expect (ml/kg/min) for elite runners of various levels. Anyone with a VO2 Max in these ranges can be sure that they have a 'good aerobic energy system':
- World Class Male: 80-90
- World Class Female: 70-80
- International Male: 70-80
- International Female: 60-70
- National Male: 65-75
- National Female: 55-65
- National Junior Male: 60-70
- National Junior Female: 50-60
Absolute values for VO2 (L/min) have been shown to be trainable by 15-20%. When reported relative to body weight (ml/kg/min) larger changes may be possible due to the effect of weight loss on these values. There is however a large genetic component to VO2 Max values often accounting for up to 30% of the difference between individuals.
As well as the VO2 Max value it is also important to look at the speed (for running/swimming) or power (for cycling) that the athlete is producing at VO2 Max (or various points on the way to VO2 Max) to get a feel for mechanical efficiency (economy of movement). It is often seen that the fastest or most powerful athletes don't always have the highest VO2 Max, but it would be uncommon for an athlete to be competing at the levels noted above without a VO2 Max within or very close to the defined range.
For events of 7-10 minutes or shorter (800-3000+m for elite runners) then an athletes VO2 Max and speed at VO2 max are the key factors for success. For events longer than this then other sub-maximal factors need to be considered and can partially compensate for a lower VO2 Max figure. This there refers to all triathlon events.
For well trained athletes with already low body fat levels changes in the absolute or relative values of VO2 Max may be difficult to come by, however improvements in efficiency/economy are possible with continued training as is the amount of time that an athlete can sustain a relative percentage of VO2 max, which we will come onto soon.
Other information that can be gained from the VO2 Max Test:
- Maximal Heart Rate (HR Max) - If the athlete is motivated enough to reach VO2 Max during the test then they will also achieve a maximal Heart rate figure for the type of exercise they are undertaking. From a practical point of view this is very useful as few people will be able to monitor %VO2 Max during training but they will be able to monitor % Max HR to control intensity.
- The Respiratory Exchange Ratio (RER) - Earlier I mentioned that whilst there is minimal CO2 in inspired air, any produced through aerobic metabolism can be measured in expired air. This allows us to compare the ratio of CO2 production to O2 consumption (VCO2/VO2) also known as the respiratory exchange ration (RER). At rest and during low to moderate intensity exercise the RER to give an indication of the fuel sources being used to drive aerobic metabolism. An RER close to 0.70 suggests primarily fats are being used for energy production whereas an RER closer to 1.0 suggests primarily carbohydrates are being used. During high intensity exercise some of the CO2 that the subject blows off comes from buffering of the blood and thus no longer reflects solely cellular metabolism.
Test 2: Blood lactate response to exercise - Lactate Threshold / Lactate Turnpoint
To understand the blood lactate response to exercise we need to consider what happens during anaerobic metabolism. Anaerobic metabolism takes place in the cytoplasm of skeletal muscle cells without the need for oxygen. It involves 11 steps and uses muscle glycogen as it's input (the first step is to convert this to glucose) and end with the production of pyruvate and hydrogen ions. Some hydrogen ions are also produced at intermediate steps in the process. As mentioned above if sufficient oxygen is present then both these substances will be transported into the muscle cell mitochondria and used in aerobic metabolism, however if oxygen is insufficient some of the pyruvate and hydrogen ions will combine to form lactic acid which immediately splits into lactate and hydrogen ions and lowers the pH of the muscle cell and begins to cause 'Acidosis'. Localised pain will be felt and a reduction in muscle cell pH will cause a reduction in muscle function. Not good.
At the onset of exercise there is always a small rise in muscle lactic acid concentrations whatever the exercise intensity as the body needs time to adapt to the increased demands placed upon it. However once this is accounted for, and the aerobic energy system has 'warmed up' , low intensity exercise will result in little lactic acid production in the working muscles due to the availability of oxygen. As exercise intensity progresses to moderate, lactic acid will begin to be produced. In addition to being 'recycled' within the mitochondria of the local muscle cell, lactic acid can be moved from the muscles that produced it via the blood stream to the mitochondria of other muscle cells to enter aerobic metabolism. Whilst the body is able to match the rate of production and removal levels of muscle/blood lactic acid will rise but remain constant as long as exercise intensity remains constant. In this situation exercise can continue in-definately as long as other factors don't cause fatigue. However at higher exercise intensities a point will be reached where removal can no longer match production and muscle/blood concentrations will begin to rise even if exercise intensity remains constant. Once this situation occurs unless exercise intensity is reduced the time to fatigue is greatly reduced and the resulting pain and loss of muscle function will eventually force you to slow down.
Lactate threshold refers to the point where blood lactate concentration rise significantly above resting levels. The speed at lactate threshold is a strong predictor of the average speed that can be sustained in the marathon. From a training point of view this can be thought of as the transition between ‘easy' and ‘steady exercise.
The lactate turnpoint refers to the point where lactate removal can no longer keep pace with production. At this exercise intensity there is a sudden and sustained breakpoint in blood lactate. Typically this occurs at 2.0-4.0 mM. This can be ascertained from an exercise intensity (running speed / cycling power) to lactate graph. For runners it can be predicted as being ~1-2 km.h-1 above lactate threshold (the difference is smaller in long distance specialists and larger in middle distance runners). It is also approximately 90% Max HR in well trained athletes. The lactate turnpoint can be held for approximately 60 mins and is therefore useful in predicting sprint distance triathlon performance for good age-group competitors. From a training point of view it is the transition between ‘steady' and ‘tempo' running.
It is best to use a step style of test to identify your lactate threshold and turnpoint. Each interval should be 4-5 minutes in duration to allow a 'steady-state' to be achieved before the blood lactate sample is taken. Because of this it is possible to use an intermittent protocol with breaks in between each step. Unlike the VO2 Max test you don't need to continue increasing intensity to maximum, only above the point at which lactate turnpoint is clear (usually 90-95% Max HR). Buy monitoring oxygen consumption during the test then the blood lactate readings can be mapped to a VO2 Max value. If VO2 Max is know then the percentage of VO2 max for each point can be monitored.
How do I make improvements to aerobic energy system through training?
This is a question to which there isn't one answer. Luckily there are a number of categories of training that can improve the capacity and efficiency of your aerobic energy system these include:
- Basic Endurance - below lactate turnpoint
- Threshold Endurance - around lactate turnpoint
- Overload Endurance - around VO2 Max
- Lactate Tolerance - near maximal intensity
Sessions including one or more than one of these categories can be constructed using continous exercise or structured intervals with periods of recovery between. Another popular form of aerobic training is fartlek. More information can be found in the article on categories of training.
As a general rule you should include all categories of training in your weekly schedule to ensure all muscle fibres types are being trained, not just the slow twitch, but the amounts of each should change depending upon your physiology, goals and the time of year. Generally you would begin with a focus on basic endurance and progress through to overload endurance, before shifting the focus back to race pace which will depend upon your chosen event. So for sprint distance triathlon this could be threshold. You should be careful with the volume of overload endurance and lactate tolerance work you do and experiment to find how much recovery you need from these sessions. You should read the articles on strength and speed training for information on other categories of training that can be included in your programme.
How can I control the intensity of my aerobic training?
Controlling the intensity of training has been achieved in many different ways across sports often reflecting the equipment available or most meaningful measure:
- Subjective - RPE (Feel)
- Physiological - HR, Blood Lactate Concentrations, % VO2 Max, Breathing Rate
- Performance Based - Pace, Power, Cadence, Load (Rep/Time x Resistance/Intensity)
In Manchester Triathlon Club sessions we tend to use pace during swim sessions, HR and power during cycling and HR and Pace during running. RPE (feel) and breathing rates can be used in all forms of exercise and are great 'tools' to learn how to use.