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[[File:Training Intensity.jpg|right|thumb|500px|A chart of different TRIMP calculations against heart rate.]]
There are various ways of measuring the impact of exercise and these measures are often termed "training impulse[[Training Impulse]]", or TRIMP ('''TR'''aining '''IMP'''ulse). The simplest approach is to use training volume (mileage or time), but it is better to use heart rate[[Heart Rate]]. There are various heart rate [[Heart Rate]] methods to establish training load with varying degrees of complexity and sophistication. It is also possible to use perceived exertion or other metrics. It should be remembered that [[All models are wrong]], especially when we are trying to model something as sophisticated as the human body. Running at an easy pace for a long distance creates different training stresses from a shorter distance at a high intensity, and the two cannot really be equated in a usable model. However, some metric is important if we are to evaluate and understand a training program. TRIMP can be used to calculate [[Training Stress Balance]], a method for evaluating the effect of training over time.
=Training Volume=
=TRIMP<sup>cr10</sup>- Session RPE Scaling=
Using a rating [[Rating of perceived exertion Perceived Exertion]] has the advantage of needing no technology. At the end of the training session (ideally within 30 min. of finishing) the athlete rates the intensity of the session using the [[Rating of Perceived Exertion|Borg CR10 RPE scale]]. This scale goes from 0 to 10+, and multiplying this session RPE value by the session time in minutes gives a value for the training load of that session. So if an athlete runs for two hours and rates this as an RPE of six, the TRIMP<sup>cr10</sup>would be 120 x 6 = 720. The units for this session load are not absolute, nor of a really comparable between athletes. The subjective nature of the RPE scale can introduce some repeatability problems. Also, the last part of the workout tends to disproportionately influence how the athlete perceives the overall exertion. However, while this method lacks the precision of a heart rate [[Heart Rate]] based training load, it does include some aspect of the athletes mood state[[Mood State]], which may be useful in determining [[Overtraining Syndrome]]. In addition, the perceived exertion may work better for workouts such as weight training, or plyometrics, where heart rate [[Heart Rate]] alone does not truly capture the training load.
=TRIMP<sup>avg</sup>- Average Heart Rate Scaling=
The simplest and most basic form of using heart rate [[Heart Rate]] to evaluate training load is to simply multiply the average heart rate [[Heart Rate]] for a workout by the time in minutes. So if an athlete runs for two hours with an average heart rate [[Heart Rate]] of 140 BPM, the TRIMP<sup>avg</sup> is 120 x 140 = 16,800. This method has the advantage of using the absolute measure of heart rate[[Heart Rate]], and the simplicity of a trivial calculation. However, the floor in this method is that the average heart rate [[Heart Rate]] does not really reflect the difficulty of a workout. Consider two workouts, each an hour-long. The first is a steady-state workout with a heart rate [[Heart Rate]] of 130 BPM. The second workout is an interval training session, where 50 min. is spent at around 120 BPM with 10 min. of intervals and 180 BPM which is also an average of 130 BPM. Both workouts have a TRIMP<sup>avg</sup> of 60 \*130 = 7,800. The equivalent TRIMP<sup>avg</sup> suggests that both workouts are equally difficult, but in practice the interval training is much harder.
=TRIMP<sup>zone</sup>- Heart Rate Zone Scaling=
A slightly better approach is based around heart rate [[Heart Rate]] zones. Instead of treating heart rate [[Heart Rate]] is a continuous range of values, it is divided up into different zones. These zones are based on the percentage of the [[Maximum Heart Rate]] (HR<sub>max</sub>). One common approach is based around the book by Sally Edwards<ref name="Edwards"/> that uses a five zones and assigns each a scaling factor as shown below.
{| class="wikitable"
!% HR<sub>max</sub>!!Scale
|-
|}
This approach works well if you are using a heart rate monitor [[Heart Rate Monitor]] that will display the times spent in each zone, but without transferring the details to a computer for more sophisticated analysis. However, there are some serious flaws in this technique. The most obvious is that a small change in heart rate could move from one zone to another, which could double the TRIMP<sup>zone</sup> score. The scaling factors are also linear, but moving from 50-60% HR<sub>max</sub> to 60-70% is far less than doubling the difficulty. By contrast, exercising at 100% rather than 90% is far harder than the 0.25 increase scaling factor would suggest. Finally, using %HRmax is inferior to using [[Heart Rate Reserve]].
=TRIMP<sup>exp</sup> Exponental Heart Rate Scaling=
=Power, Lactate, VO<sub>2</sub> Scaling=
While heart rate is generally the simplest and most effective way of calculating training impulse [[Training Impulse]] there are other approaches. For cyclists, it is possible to directly measure power output and to use this to calculate training impulse[[Training Impulse]]. However the training impulse [[Training Impulse]] values calculated from power cannot easily be translated for integration with other training methods. It is theoretically possible to calculate training impulse [[Training Impulse]] based on lactate levels or VO<sub>2</sub>, but in practice it is impractical to measure these well training.
=References=