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Calculation of training load

Up to now, training load has been calculated on the basis of how the athlete has determined the intensity of the workout in workout completion (RPE). A workout could receive between 0 and 10 intensity points. The training load was calculated as the product of the training duration in minutes and the intensity.

For example, if a workout was defined as Easy (2) and lasted 60 minutes, its training load was 120. This value is expressed in AU (Arbitrary Units) — a unit that comes from the session-RPE method developed by Carl Foster. It is called "arbitrary" because it is not a physical or physiological unit (like watts or beats per minute), but a relative score used to track training trends and compare sessions for the same athlete over time. We report all calculation methods in the same AU unit, so the values remain comparable regardless of the method used.

The majority of running workouts usually fell between 2 and 6. It is important to remember that the intensity of a workout should be determined in a unit of time. That is, training intensity was not affected by whether the workout lasted five minutes or two hours. The duration only affects the training load value.

There are three methods for calculating training load:

  • Accurate calculations
  • General calculations
  • Simple calculations

Accurate calculations and General calculations are based on an algorithm using the athlete's heart rate during training for the calculation. Simple calculation is an existing method based on the RPE determined by the athlete after training.

Important

In order to use the Accurate Calculation or General Calculation method, it is necessary to enter the athlete's Maximal Heart Rate and Resting Heart Rate in their Performance Data. The algorithm takes into account the so-called heart rate reserve, so it is the resting heart rate that is important for the calculation.

Accurate calculation​

This most accurate method of calculating training load uses detailed workout data imported from an external service (e.g. Garmin Connect) and containing heart rate data during the workout. If the workout is added manually or the workout has no heart rate record, this method will not be available.

How do the calculations work?​

The workout is divided into 60-second segments and for each such segment a partial training load is calculated, which can be assigned to that segment based on the average heart rate of that particular segment.

The value of the training load does not increase linearly with increasing heart rate. Taking into account the fact that more intensive workouts affect the recovery time considerably more (not only because of the strain on the cardiovascular system, but also because of the fatigue of muscles and other systems in our body), we have adopted a power function for the calculation, so that the load rises non-linearly, at an ever-faster rate. Thus, the closer we are to the maximum heart rate, the higher the rate of increase in intensity.

Example

Athlete minimum heart rate 45, maximum heart rate 190. Training 60 minutes average heart rate 140 - training load 92 Training 15 minutes average heart rate 170 - training load 105 As you can see the recovery after an hour of easy running will be faster than after 15 minutes of very intense running.

In the "Accurate calculations" and "General calculations" method, we also took into account the duration of the workout. This means that as the length of the training unit increases, for the same intensity of the entire workout, the training load increases gently in a non-linear (accelerating) rather than linear manner.

Example

Our athlete above, training 180 minutes heart rate 140 - training load 311 With two separate workouts (e.g. morning and evening) of 90 minutes each, at the same heart rate - the training load will be 145

Thus, the training load of a three-hour workout will not be the simple sum of the training loads of two separate one and a half hour workouts at the same intensity.

The Accurate Calculation method is most beneficial and precise for calculating the load of training units where there is high variability in heart rate during training (e.g. intervals). As there are rest periods between intervals where the heart rate drops significantly, this can affect the average heart rate of the entire workout, which despite the high intensity of the intervals will have a low average heart rate value, which again can result in an underestimation of the training load.

General calculations​

If no training downloaded from an external service is available for a workout completion, it is possible to calculate its training load using the General Calculation method. In addition to the athlete's maximum and resting heart rate data in the Performance Data, it requires the athlete to specify an average training heart rate when adding the completion.

This method makes a simplified calculation based on the average heart rate of the entire workout. It does not divide training into small units. This may underestimate the training load of training units where there is a large variation in intensity (e.g. intervals).

This method takes into account the length of the workout, as mentioned when discussing the 'Accurate calculation' method.

Simple calculation​

This training method is a way of calculating training load based on the athlete's subjective perception of training intensity (RPE) and the length of training time.

Is this the same as TRIMP?​

In short — yes, in essence. Our training load belongs to the same family of metrics as TRIMP (Training Impulse). Both methods use heart rate reserve (the gap between your resting and maximum heart rate) to measure the intensity of effort and combine it with the duration of the workout.

Our algorithm goes a step further than classic TRIMP:

  • Whole-session analysis, segment by segment. When full heart rate data is available (from Garmin Connect, Polar Flow, Strava, etc.), we split the workout into segments and calculate the load for each one. Classic TRIMP usually relies on a single average heart rate for the whole workout, which can underestimate the load of sessions with variable intensity (e.g. intervals).
  • Stronger emphasis on intensity. We discriminate more sharply between high- and low-intensity effort, so a hard session is clearly distinguished from an easy one of the same length.
  • A duration adjustment that reflects how longer sessions accumulate fatigue.

The one meaningful methodological difference is that classic TRIMP applies a small correction based on sex, which our model does not currently take into account.

Choice of method in applications​

The application provides the option to select the method used. By default, the best available method is used, depending on the data you have:

  • if HRmax and resting HR are specified and the workout is imported from an external service - Accurate calculation

  • if HRmax and resting HR are defined and you have an average heart rate entered into your training - General calculation

  • otherwise - Simple calculation

  • However, you can switch to another available method at any time. For example, if we know that the heart rate records are not correct during a workout (e.g. due to a watch malfunction), we can switch to the "General calculation" method and enter the average heart rate manually into the workout completion. Or switch to Simple calculations at all.

Switching the method is available on the workout completion view in the mobile app and the web app. Next to the training load value, we have an icon that you can click to display the methods of your choice. Switching to a different method only works for the selected workout. Both the coach and athlete can change.

Training load on graphs​

In the Reports section of the browser application, we have the option to select to view the training load statistics from the last time, both on a daily, weekly and monthly basis.

You can also select a graph showing the training load according to the old RPE method.

Training intensity​

From the training load values calculated according to the new algorithm, we also calculate the training intensity. This can be viewed in the graphs.

When determining the intensity of a workout using the Accurate calculation method, it is specific that training segments whose heart rate is lower than the average heart rate of the entire workout are not taken into account. This ensures that exercise intensity (but only intensity) is not affected by rest segments in interval training, warm up or cool down.

Example

An athlete completed an interval workout of 6 x 400 metres, the warm-up was a relaxed 20 minutes. The average heart rate of the entire workout was 145. The average heart rate of the warm-up was 138. The average heart rate of the cool-down was 140. The average heart rate of the fast sections was 165. The average heart rate of the slow sections was 144.

In the example above, the intensity of the workout is only affected by the fast episodes because they are the only ones above the average heart rate of the whole workout. This will allow us to see the intensity that the workout had when the athlete was working hard and not resting.

It is important to remember that intensity is a time-independent value (as is RPE).

The intensity of the workouts can be viewed in the Reports section of the web application.