› Triathlon Physiology, Training & Racing

Triathlon Physiology 
How Does This Relate to Racing And Training?

Want to know more about how triathlon physiology relates to actual performance and training so that you can train more effectively?

This guide will provide you with enough real world information to understand the basics of which parts of triathlon physiology are important and how it relates to training.

We miss out a lot of stuff….if you want to know all this, go to university or read more academic sites! If you want to learn how to go faster stick with Intelligent Triathlon Training!

Why Train At All?

1. Training forces your body to adapt when you do more work than the body is used to – you get fitter

2. A lack of training or sufficient exertion and your body regresses – you get less fit

3. Too much training and your body stops working properly and you get tired, ill and injured – you don’t adapt effectively and waste a lot of time and effort.

Therefore training is all about getting the balance of training just right to maximise your race performance.

How Your Body Adapts To Training

Adaptation is the key to improving performance, and there are two types of adaptation:

1. Chronic– these are structural changes to the body that take longer to occur, but also last longer and potentially make bigger differences.

These adaptations include:-

  • Increased capillarisation in the lungs allowing more oxygen to be extracted from the lungs and transferred to the blood
  • Increased heart chamber size, resulting in the capacity for more blood to be pumped during exercise (maximal cardiac output)
  • Increased capillaries in the muscle allowing more blood to flow through the muscle and release the oxygen
  • Increased mitochondria in the muscles(where the energy is produced)

In other words, more oxygen, pumped at a greater rate, to more conversion centres = more energy for exercise!

2. Acute - these occur over much shorter time periods, but can also fade quickly, including but not exclusively:-

  • Increased blood volume through increased blood plasma
  • Increased red blood cell count and size of cells – these enable more oxygen to be transported by the blood.

Understanding Energy, Triathlon Racing And Performance

Triathlon in any form is an endurance exercise (despite the SPRINT distance….all things are relative!). Therefore you need a combination of oxygen and fuel to make energy to meet the demands you place upon it, just like our car example.

A car requires:

oxygen + fuel + combustion engine = energy


Energy + accelerator = control of speed.

A human requires:

Oxygen + food + you = energy


Energy + muscles + brain = control of speed.

If you don’t put enough fuel in and you train with your right foot flat to the floor you will run out of fuel very quickly, need another service or some major repairs and therefore miss time to train.

So you must provide sufficient energy and train at a sensible level to achieve the consistency you need to improve. We will talk more about the actual programmes in the Swimming Training, Bike Training and Run Training for Triathlon pages.

The adaptations to training take place most effectively when you are recovering, so continuing to train over long periods hampers your body’s ability to adapt.

Unleaded Or High Octane, Which Is Better For Triathlon?

Where the car differs from you is that you have two types of fuel, one that is fairly unlimited (fat) and is very efficient, and one that is quite restricted (carbohydrate) and is relatively inefficient.

Have a look at our nutrition for triathlon pages for information about filling your petrol tank!

The main reason to use fat is that in even the leanest individual it is effectively an un-limited supply (certainly within the context of triathlon physiology). Carbohydrates on the other hand are in limited supply.

The advantage they have is that when work rates are very high, they can be converted to energy much faster than fats, therefore the body chooses them to meet its needs, despite a lower energy yield per gram.

It’s the rate that’s key. However you can only store enough carbohydrate for about 90 minutes of high intensity exercise, if fully loaded!

Your ultimate aim from triathlon training is to train your body to use fat as its fuel source at higher speeds or powers. The faster you swim/bike/run before you rely on carbohydrates to fuel your performance the faster you will race.

The other trick is increase the amount of oxygen you can use to help convert the fuel to energy, i.e. VO2max. The more oxygen available in the muscles the more energy you can produce.

An Introduction To The Big Three Triathlon Physiology Factors That Limit Performance

VO2max the maximum rate at which you can use oxygen (measured in l/min or ml/kg/min).

Economy & Efficiency – simply put, this is how effective you are at using the oxygen you have extracted from the air you breathed in. The more economical you are, the less oxygen you need to go at a particular speed. See the running economy page for more detailed information.

Fractional Utilisation (FU) – the percentage of VO2max you sustain for whatever duration you are racing over. So for short races this will be higher than for Ironman events. Trained athletes are able to sustain a higher percentage of their VO2max, for the same duration of a race as an untrained person….why?

Read on!

How Do The Big Three Effect Triathlon Performance?

  1. A trained person has a considerably higher VO2max than a less well trained person. Therefore they theoretically have more oxygen available to produce energy.
  2. A trained person will be closer to VO2max before they begin to use carbohydrate as well as fat to fuel exercise – Threshold 1 (T1). In trained athletes this can occur as high as 60% VO2max. However in less well trained people it might be as low as 40%. The percentage of your VO2max that you can sustain at Threshold 1 will dictate your performance over the longer endurance races – for example the Ironman distance.
  3. A trained person will be closer to VO2max before they rely predominantly on carbohydrate – Threshold 2 (T2). This can occur as high as 80% VO2max. However in less well trained people it might be as low as 65%. The percentage of your VO2max that you can sustain at Threshold 2 will dictate your performance over the middle distance endurance races – for example the Olympic distance.
  4. These are both examples of Fractional Utilisation, but they are not exclusive examples. In short, fractional utilisation is the percentage of maximum you can sustain for whatever duration you are racing over.
  5. For any duration there is a limit to how close to VO2max you can exercise. For instance you will only be able to maintain VO2max for a few minutes, whilst 80% VO2max could be sustainable for about 60 minutes and 60% for a few hours. It is not possible to sustain 100% VO2max for 30 minutes continuously.
  6. This doesn’t tell us how fast anyone is going, just how close they can get to VO2max for any duration.
  7. VO2max is largely genetically decided, however training can improve it. Therefore it is possible that untrained individuals can have a high VO2max, however they will not have all the adaptations that come with training. This is an indicator they may have potential to be an ‘elite’ but it is not a guarantee. You cannot be ‘elite’ without a good VO2max though!
  8. How economical you are will affect the energy cost of exercise. If you have a good economy you will require less oxygen than another person, at the same speed. If you then have a higher VO2max you have the potential to perform better. You still need to train to make the critical adaptations though!
  9. Economy can change during the event. As you fatigue, the energy cost of running at the same speed increases. There are many reasons for this.
  • If this happens you usually slow down, so the energy cost is the same, but the speed is lower.
  • A training programme must try to improve this, especially on the run.

The table below illustrates the differences in VO2max and FU between elite and non-elite athletes.

VO2max (ml/kg) LT1 VO2 (ml/kg) LT2 VO2 (ml/kg) LT1 Speed (km/h) LT2 Speed (km/h)
Elite 80 46 (57.5% of max) 64 (80% of max) ~ 15 ~18.5
Non Elite 55 30 (54.5% of max) 41 (74.5% of max) ~ 12.5 ~14

How Does The Race Distance Impact On Triathlon Physiology?

For races like the Sprint distance, the duration of the event is shorter, which means you can get closer to the T2 during your race. From the Nutrition for Racing page we know that energy availability is not usually a limitation, so improving your T2 and VO2max will enhance your race performance.

However thinking long term, it is a good idea to work on improving T1 as well, as this will help to improve your T2 over time. This leads on to periodising your training to keep improving and to stop you becoming stale. See here for our top tips on constructing a periodised plan (coming soon).

In an Ironman race lasting many hours, carbohydrate is not going to last for long, so trying to maintain T2 for any serious duration is going to end in disaster!

Training for an Ironman event must concentrate on improving your reliance on fat as a fuel source, i.e. raise T1 as the main priority of the programme.

Remember it is the time that the race takes you that is important, not the distance. Your body does not realise you have covered 60-miles or 100-miles, but it does know how long you have been going and how fast you have been burning your energy stores!

The table below indicates the relative importance of the key areas to concentrate on for each event in triathlon, including an expected race time. So if you are a novice Olympic distance athlete and you are aiming for 3-hrs, then you are probably looking closer to the 70.3 guidelines and so on.

Key areas of triathlon physiology impacting on race performance:

Sprint Olympic 70.3 Ironman
Time 60-80-min 2 – 2.5-hrs 3.5 – 4.5-hrs > 8-hrs
VO2max High Medium Medium/Low Low
Economy Low Low Medium High
T1 Medium Medium High Very High
T2 High Medium Medium Low

A Quick Recap Of Triathlon Physiology!

With regards triathlon physiology, performance is mainly improved by increasing your capacity (VO2max) and improving your conditioning or fractional utilisation (raising your T1 and T2)…..in all three disciplines! Who said it was complicated?

Just to clarify then, you can see from the table that the Elite athlete has a VO2max of 80-km/kg/min, against the non-elite’s 55-ml/kg/min. You can also see that the Elite can run at a speed of 18.5-km/h at T2 with an oxygen consumption that is higher than the non elite’s VO2max.

The non-elite can try to improve their T1 or T2 as much as they like but until VO2max is increased they will not compete with the Elite. They can aim to improve their own performance but they need to set realistic goals.

So the key areas of triathlon physiology to improve your performance over all distances are:

  1. Increase your reliance upon fat as a fuel at the highest speed you cana. A higher T1 is the outcome
  2. Increase the speed at with you solely burn carbohydrateb. A higher T2 is the outcome
  3. Improve your VO2max (or ceiling)

You can improve performance by improving your economy. However this is much more difficult to do and usually has only small gains.

For more tips on how to train these areas in each of the disciplines see our swim, bike and run training pages.

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