Training Effect – what is it and do you take notice of it?

June 21st 2021

By Matt Hill
Categories: Athlete Resources

Training Effect – what is it and do you take notice of it?

Triathlon and technology seem to go hand-in-hand; do you know a triathlete that doesn’t have a gadget of some kind? Some even have several models for different occasions or disciplines.

Now that technology is cheaper and more accessible than ever, it is easy to invest in and access the many insights they offer. However, as advanced as they are, many are temperamental and in our experience are regularly inaccurate. For the athlete, they are often confused as to how to operate the sometimes-conflicting functions; they are often hugely distracting and take the users attention away from the session and more importantly, from adopting self-diagnosis, or feeling.

This being said, there are some features that are well established and offer a good insight into your training and state of wellbeing – providing you understand what they are telling you!

Training Effect (TE)

A commonly embedded function across most brands of sports technology is Training Effect, simply displayed as “TE” and is presented as a simple numeric.

TE has been around for many years and is helpful for monitoring the stress associated with training. Using this function alongside your own self-awareness can be a quick and easy way of tracking fatigue and load management.

However, do you know what TE really is and what the numeric display means? We see three reactions when it comes to reading TE:

  1. Understands it and uses it to progress training more accurately.
  2. Ignores it – either doesn’t understanding what it is or not even aware of it.
  3. Assumes a HIGHER TE is better and works harder next time!

What is Training Effect?

TE is the measurement of stress that an activity has on your body in terms of aerobic and anaerobic fitness; TE accumulates during the activity / training session and as the activity progresses, the TE value changes.

The science behind Training Effect (TE)

TE was developed by a group of scientists who initially integrated TE functionality into Suunto devices (and went on to form the company Firstbeat). TE is now widely incorporated into almost all common sports technology brands, including Garmin, which is probably the most widely used.

TE is a representation of the disturbance an activity has on homeostasis; this is the constant process where the human body is always working to maintain stability, or to stay in homeostasis, by balancing internal physical, hormonal and chemical conditions.

Training causes an imbalance by adding stress and TE is a measure of this and is based on a combination of factors. The “stable” position is taken as being the information you, the user, inputs for your user profile (age, gender, etc – the baseline data); the effect of training. The imbalance is then captured by monitoring your heart rate (HR) data during the training sessions.

Using your baseline attributes, your heart rate data in each training session is used to estimate your Excess Post-exercise Oxygen Consumption (EPOC). EPOC can be accurately measured in laboratories using respiratory gases during exercise; Firstbeat developed an algorithm that predicts the EPOC without the need to visit labs. Further details can be found in a White Paper published by Firstbeat.

TE is an evolving parameter as it is continually “learning” how you respond / manage your training over time.

What does TE tell us?

Basically, TE indicates the expected effect a training session has on your fitness and fatigue levels. EPOC, and so TE, increases when either exercise intensity or duration is increased as this necessitates additional (adequate) recovery. As fatigue builds, over days/weeks, HR will typically remain at a higher level indicating increased stress levels.

When used correctly, TE allows training to be adapted according to the impact of previous sessions by altering the volume, intensity and recovery periods as necessary.

 TE is expressed as TE: Aerobic and TE: Anaerobic.

Training Effect: Aerobic / Anaerobic

AEROBIC TE is a prediction of the effect or the activity on your aerobic fitness levels, specifically your VO2max which relates to the lower intensity training that is required to be more efficient at endurance activities. Simply, the greater your aerobic fitness, the better (faster and more resilient) you will be in endurance events (which includes sprint triathlons).

ANAEROBIC TE predicts the effect on your ability to perform short bursts of high-intensity activity ABOVE your VO2max. Anaerobic fitness and so anaerobic TE is useful for team sports, where participants are required to sprint many times over short durations among sustained easier efforts. This type of activity / training depletes glycogen (stored sugar) quickly and cannot be maintained for long periods.

Figure 1: typical structured training to enhance AEROBIC TE

 Aerobic or Anaerobic work for triathlon

Given that triathlon, from sprint to long course, is an endurance event, training the aerobic system, and monitoring AEROBIC TE MUST be the focus for all training sessions (but not necessarily focusing on their VO2max data – more on this later). By developing aerobic fitness, you are developing your ability to endure in long distance events.

The Anaerobic TE feature is therefore not as relevant to an endurance athlete who needs the ability to perform efficiently for long durations at lower intensities. Remember that the anaerobic TE calculates the stress on the body from bouts of activity that are ABOVE VO2max which are VERY HARD / short efforts of 10-120seconds and require long recovery periods and are therefore much more likely to result in injury and overtraining.

We contacted Tero Myllymäki, Physiology Research Manager at Firstbeat, for his thoughts on using TE to benefit a triathlete. His opening remark points directly to the importance of developing aerobic capacity:

 “In triathlon, especially with Ironman / full distance the most important capability is that you endure, so it would require long training sessions where an athlete is developing aerobic metabolism, fat burning, oxidative enzymes, mitochondria, fatigue tolerance etc. The training load and volumes could be reached by trying to “spread” the training to higher number of training sessions rather than lower number of sessions, if possible.

With this approach an athlete can be quite fresh for each session but still reach high overall training volume. And I believe this is less risky approach and would also make recovery easier, as the athlete is not doing so demanding individual training sessions. If this kind of approach is used, then I would recommend the lower end of TE scale.

TE scale 0-5

 Both the aerobic and anaerobic TE have a scale of 0-5 to identify the impact of the activity:

0.0 – 0.9 = no effect

1.0 – 1.9 = minor effect

2.0 – 2.9 = maintaining effect

3.0 – 3.9 = improving effect

4.0 – 4.9 = highly improving effect

5.0 = overreaching/overloading effect

The latter of our three types of people “using” TE strive to get a 5 out of 5 from every session – and soon fail!

5 out of 5 should NOT be a regular goal of any athlete, whether referring to aerobic or anaerobic TE. A TE of 5 means that the body has been substantially knocked out of homeostasis that requires substantial recovery; we would ONLY expect to a TE of 5 following a specifically placed training session or from race day.

For endurance athletes, most of their focus should be on the aerobic TE; whereas, for team sport athletes, the anaerobic TE. Endurance athletes, (and team sport athletes) will get a cross-over; this is most likely to occur in sessions that include strength or speed work. Even so, the anaerobic TE should not exceed the Aerobic TE for endurance athletes which requires a smart approach to the management of training (by the coach) and control (by the athlete).

Firstbeat describe Aerobic TE and Anaerobic TE with recommendations of use and examples of session content in Table 1 and Table 2 respectively.

Table 1 – Aerobic Training Effect

Table 2 – Anaerobic Training Effect

There’s no need to target VO2max

Aerobic TE is primarily based on improvement in VO2max. As previously discussed, we don’t train our athletes to target VO2max as the training is HARD, is not sustainable or optimal for long periods of time. This is especially the case for both new athletes or the more experienced athletes who train two or more times a day.

Remember that the physiological adaptations that occur when performing lower intensity / aerobic training will aid to increase VO2max and, as Dr John Hellemans, Sports Medicine Practitioner and coach said, “A high VO2Max indicates a high level of aerobic fitness…” but “…is not a good predictor of race performance

From a coaching point of view, we aim for the all-important consistency in training and most of our athletes train every day, and often more than once each day and so we don’t want them to be to become too fatigued.

Using Table 1 for Aerobic TE for an example of how to interpret TE using Firstbeat criteria: a TE of 4 – 4.9 will be a “highly improving” session. However, to achieve this the session would need to be “vigorous” and “around the lactate threshold” and would therefore require “more attention on recovery”

On the face of it, this sounds ideal but the need for “more attention on recovery” often means a train-no train approach and so a sacrifice of total training time, not performing well in subsequent sessions or even missing them.

The overall result is then a lack of consistency, which is the key to success.

We advise that our athletes have a TE of no more than 3.5 in most of their sessions but NOT all sessions. A TE between 1.5 and 3.5 allows consistent training and consistent recovery – and consistent improvement.

Regularly seeing a TE of 3.5-4 will drive your TE upwards and eventually you will become overtrained, injured or simply burnt out. This is training the middle ground, the grey zone, developing the one speed syndrome / aerobic deficiency syndrome.

Polarised Training

We apply the polarised training model to our coaching which means that at least 80% of ALL training is EASY (low intensity, aerobic or in TE terms, <3.5). the remainder of sessions, less than 20%, are at high intensity (HARD), with little at a MEDIUM intensity. This approach is used by pretty much EVERY successful endurance coach and or athlete as clearly demonstrated by Prof. Stephan Seiler in his analysis of the training intensity distribution of a range of elite endurance athletes.

Tero expands some more:

During the recent years, the training programming has favored polarized training where there is a lot of very easy training aiming to develop aerobic base together with very hard sessions.

This makes sense as an athlete is able to tolerate quite high amount of easy training and then you sort of take the most benefit from the hard sessions, and may be able to get the most out of it by avoiding the “middle area” that often is quite demanding and requires time to recover from, although not giving the best effect for the maximal performance”

I wouldn’t be too afraid of sometimes reaching TE in the area of 4.0 and higher, because this would be good for lifting the VO2max. When the athlete is getting this kind of benefit, he/she is then also able to get more out of basic endurance training (as the performance level is higher). But of course, if there is a lot of this kind of training, it then requires more time for recovery and that time is away from building the endurance.”

Physiological Drift

TE tracks the HR (and therefore overall physiological) response to training load. Each training session builds on the stress already in place from previous sessions – which should have been reduced by rest/recovery, active recovery or some form of complementary training.

Training by fixed metrics (power, pace, speed, etc) combined with an over-emphasis of high intensity sessions (HIT) AND having a high day-to-day life stress (work, family, etc) is particularly likely to increase TE levels towards the overreaching effect. Your body will be continually stressed, preventing the natural homeostasis process to conclude and this will be detected by displaying an upward trend in both TE and recovery time.

For triathlon, an “improving” session (TE of 3.0-3.5) once a week in each of the disciplines combined with two or more maintaining effect sessions (TE of 2.0-2.9) is enough to improve aerobic fitness without overreaching or potentially causing health / injury issues.

Recovery time – how long!?

Recovery Time is also a parameter widely featured along with TE and indicates how long it will take your body to fully recover following a training session, i.e. regain homeostasis. You will probably have seen it displayed at the end of a session and indicate something like: “Recovery Time – 15hours”?

The recovery time will be appropriate to the type of session just undertaken, accounting for the combined effect of the duration and intensity. Sometimes you can relate to the figure, other times it may surprise you – in a good or a bad way! Recovery times are in the range 0hrs up to 4 days.

As with TE, recovery time is often misunderstood or ignored, and just like aiming for consistently high TE’s, a long recovery time is seen to be a good thing – no pain, no gain, right?! WRONG.

There are a couple of factors to consider:

  1. It is easy to consistently train too hard (getting high TE’s) which results in a higher level of fatigue; this becomes “normal” and it becomes accepted that the feeling of fatigue, with the consequent long recovery times, is “normal”
  2. There may have been errors in reading your heart rate, etc (as does often occur). If you get abnormal TE or recovery times but feel ok, check the connectivity and the HR graph – look for sudden and regular drops or increases in HR.
  3. Everyone is subjected to other life stresses and these will have an impact on your TE – training stress adds to life stress to result in a combined higher stress, and higher TE.

However, disregarding errors and considering other factors, you should take notice of the recovery time indication as it will be reasonably accurate.

It is important to remember that you can, and should, still be active during this recovery period. Active recovery, in the form or easier training (swim and bike, not running), with a TE of 1-1.9, or a complementary training session can help to lower (accelerate) your recovery. For example, if you have a recovery time indication of 15hours you could perform a low intensity session several hours later and the resultant (overall) recovery time after this session could be lower than if you had just rested.

This is where coaching, or good management of sessions Is important allowing you to train and still recover, as Tero advises athletes:

After these kind of harder sessions, I would prefer for example very easy cycling where TE could be in the area of 1.0 – 1.9, i.e. fully aerobic work where you still get some work for the body, elevate circulation and facilitate recovery process but at the same time also get some impact on aerobic metabolism.”

It is important to remember that recovery is a key component of training and the amount of recovery you need is linked to the intensity and duration of your activities as well as your other daily activities and stress.

Giving your body time to recover and adapt is vital to your ongoing progression, ignore it and you will likely become injured and/or suffer overtraining.


TE and recovery time is recorded and available to almost all athletes now and is presented following every training. As a triathlete you need to prioritise your AEROBIC training, and to be more focused on your AEROBIC Training Effect. A TE at the lower end of the range: 1 – 3.5 is more desirable, as this indicates that you have worked aerobically, and that you can consistently recover from each session.

If you train every day, and/or two or more times per day without managing the load and recovery then you can easily burn out!

Take note of your TE and the recovery time so that you can adapt your training schedule and make sure that you don’t reach a point of being overtrained.

Getting the right mix of training intensity and recovery will allow you to progress smoothly, healthily and be less susceptible to injury; get it wrong and it can result in short peaks and long troughs in your fitness, as well as your mental and physical wellbeing.