Workouts can be quantified in many ways – runners and cyclists are always being asked ‘how far did you go today’, or ‘how long were you out for’. Usually they can impress the questioner with a response like ‘I did xx miles’ or I was out for ‘x hours’. But of course simply stating the distance or time takes no account of the speed or intensity, and tells nothing of how hard you found the effort.
As a runner, you can do 1:30 easy talking pace and just feel refreshed at the end, or you can do a 10km race in less than half that time and feel completely exhausted at the end, with leg stiffness and cardiovascular fatigue that persists for several days.
So what’s really needed is a measure that takes into account both time and intensity in order to allow us to compare the effects of training sessions between individuals. That sounds clear enough, and surely sports scientists must have a standard way of doing this that works pretty well? Actually, no, there is no one perfect objective way of measuring training load, for the simple reason that the human body is a complex organism with multiple energy systems overlaid with hormonal signals of multiple kinds.
One of the most widely used methods is not objective at all, and in fact just requires the person performing the physical work to answer a question honestly. Gunnar Borg was a psychophysiologist studying the effects of physical work and devised a scale that had verbal expressions allowing someone to point to a number between 6 and 20 that represented the total pain or effort they were perceiving. He later invented the CR10 scale which is still in widespread use today, especially in clinical & lab tests, and in speed & power sports. There is a variation, introduced by Dr Carl Foster that multiplies the effort rating by time to get a ‘Session RPE’.
Training IMPulse or TRIMP is not a single measurement method, but is a collection of ways of combining a relative effort and time component into a single number. TRIMP includes proprietary variants such as the Training Stress Score (TSS) created by Dr Andrew Coggan for use by cyclists training with power meters, based on a score of 100 for a 1 hr maximum sustained effort. This is also used in the Training Peaks software. An intensity factor (IF) is then used for power (effort) levels higher or lower than this.
Most TRIMP calculations are based on Heart Rate measurements over the course of a workout, since increasing HR reflects increasing effort. Although heart rate is easy enough to measure continuously using a wireless HRM chest strap (or perhaps optical sensors), it has two characteristics that need to be understood in order to use it effectively:
- Individuality. The relative effort of one person vs. another at the same heart rate can vary widely. A 16 year old soccer player might get their heart to 170 bpm with ease, whereas an older, less fit person would struggle to achieve this even with maximum effort.
- Delayed response. When effort level increases suddenly, the sympathetic branch of the nervous system stimulates production of adrenaline (epinephrine) but it might be 30s before the heart rate is stable at the new level. Similarly, when effort levels fall, heart rate also has a delayed response. This makes TRIMP calculations based on average heart-rate (such as Banister TRIMP) less useful than ones that use dynamic values. There is still no good solution for this characteristic, making heart-rate less useful for sports and workouts that involve short bursts of very intense activity.
To handle individuality, there are a couple of methods that are useful. The best involves an individual calibration of blood lactate against heart rate (iTRIMP, Abt, Akubat, Manzi) but this requires lab testing not available to most non-professional athletes and team sports players.
Lucia proposed a category version of TRIMP, where time at a heart rate below the individual’s first lactate threshold would be given 1 point per minute, time above the 2nd lactate threshold 3 points per minute, and time in between the two thresholds 2 points per minute. Although not fully individualised, this method has the advantage that the thresholds can be reasonably well estimated using the person’s age and fitness level. The first threshold can be estimated using Dr Phil Maffetone’s 180 Formula. The second threshold (at which breathing becomes ragged & uncontrolled) can usually be found between 85-90% of the maximum heart rate. Carl Foster has recently published work to show that these thresholds can be estimated quite well using breathing tests that anyone can perform during a graded workout.
The Lucia TRIMP method is the one we have implemented in the Precision Pulse Heart Rate Monitor (HRM) app. All the user has to do is fill out the Settings screen as accurately as they can. Knowing the true maximum HR and being honest with the fitness level setting will help a lot!
The chart below shows an example workout where the TRIMP score can be seen as the blue line, whose slope changes according to the intensity at a particular time. The accumulated total for this workout is 103, as shown in the top right of the screen. The background colours show the region; below first lactate threshold (green), above 2nd threshold (red) and in between (yellow). When the workout has finished (after 1:25), the heart rate falls, and no more TRIMP points are accumulated.
ithlete Precision Pulse is a precision heart rate monitor app for iPhone, iPod Touch and iPad that works with analog HRM chest straps and allows you to use GPS run & cycle tracking apps & listen to iPod music all at the same time. To read more about Precision Pulse features or the required hardware why not visit our product page?