TRIMP, which stands for TRaining IMPulse, is a measure of training load, the amount of fatigue a ride generates. The longer the ride, the greater the fatigue. The more intense (harder, faster) the ride, the greater the fatigue. TRIMP is calculated by multiplying the length of a ride in minutes times a measure of intensity of that ride. The different curves shown above above illustrate different ways of estimating intensity. Lucia, Edwards, and Banister TRIMP are well known and are well described in the literature. Gillen and Hughes are defined by me and thus essentially unknown. I defined Gillen intensity in a previous post, and Hughes intensity in this post. The point of this post is to argue that I the well known versions of TRIMP significantly underestimate the amount of fatigue generated by high intensity rides. (Note that the above scale is a log scale; the differences illustrated are quite large.)
“It Ain’t What You Don’t Know That Gets You Into Trouble. It’s What You Know for Sure That Just Ain’t So” - Anonymous
How does one estimate the amount of fatigue a workout generates? The standard metric used by many coaches and academics is a metric known as TRIMP, which stands for TRaining IMPulse, a term that means training load. As is well known, training load produces fatigue in the short term and, when combined with recovery, increases fitness in the long term. In this post, I will only be considering the fatigue impact, and in that context, TRIMP is also synonymous with fatigue.
TRIMP is not a single metric but rather a collection of different metrics. A TRIMP score is calculated by multiplying the minutes of exercise by the intensity of that exercise, which just kicks the can down the road: how does one determine intensity? The difference between the various TRIMP metrics comes from their use of different estimates of intensity. I wrote my previous post in this series, “Training Zones, Calories, Oxygen, and Power”, to provide the background needed to understand where estimates used by the more common versions of the TRIMP protocol come from; they come from the closely related metrics of heart rate, blood lactate, power, and the training zones derived from these metrics, all of which ultimately relate to calories burned per minute. In the absence of any information to the contrary, is it a reasonable guess that fatigue might be directly related to the rate at which calories are burned? Sure, why not? However, it is just as reasonable to guess that that it is not. What I am going to argue here is that there is information to the contrary, that the advice commonly given by coaches based on their real world experience provides a very different estimation of how fatigue relates to intensity than would be predicted by the amount of calories rides of different intensity consume.
How do the common versions of TRIMP estimate intensity? Edwards TRIMP is based on a heart rate-based five zone system and uses the zone number as the measure of intensity. Lucia TRIMP uses a blood lactate-based three zone system and again uses the zone number as the measure of intensity. Banister TRIMP does not use training zones but rather uses heart rate directly. In addition, it adds an exponential adjustment which reportedly was included to make it match lactate levels more closely. The effect of this correction is relatively small, however. There is also something called individualized TRIMP. I believe this represents a family of estimates with one source even using the term to to refer to Banister TRIMP^. The purpose of this post is for me to provide my own estimate of intensity which can be used in my own version of TRIMP, an estimate based on the actual training plans provided by Coach John Hughes.
This is not my first attempt to provide a different measure of Intensity. My first attempt was based on the paper I refer to as Gillen et al. This estimate was based on a 7 zone system, and I suggested that Zone 7 produced not 3.5 times the fatigue of Zone 2 but 45 times as much, that the estimates of intensity for Zone 2 and Zone 7 should be not 2 and 7 but 1 and 45. I think that fatigue generation and intensity is most definitely more complicated than that, that there may not even be a single number that fully represents each zone, but in the interest of not allowing the best be the enemy of good, such a single number representation is what I will be developing in this post not because I think it is perfect but because I think it is better than the other more commonly used estimates. To put this into perspective, in my last post I essentially used a multiplier of 1 for all zones because I lacked the zone data to do better. Had I been able to use the zone number multiplier I am now disparaging, that would have been better than what I did. I think this is why coaches sometimes recommend a zone number multiplier, it is simple so that their athletes might actually do it and it is better than nothing. In that spirit, I think there is an even better multiplier that coaches could add to their training zone charts that would be, if not perfect, an improvement over zone number (and just as simple). In fact, I think that multiplier is implicit in their more detailed training advice, and what I am going to do in this post is to tease that out for one publication of one particular coach, the one coach I am currently following, Coach John Hughes. The main theme of this post is going to be to compare what Coach John Hughes recommends to what he would recommend if it were true that Intensity was proportional to Training Zone Number (e.g. Load = Minutes x Zone Number.)
Let’s imagine a healthy, young athlete who is a randonneur specializing in 200K brevets. Let’s imagine they select "Distance Cycling" by John Hughes and Dan Kehlenbach (hereafter referred to as Distance Cycling) as their training guide. This is the plan for preparing for a 200K brevet from Distance Cycling:
The numbers are the length of each day’s ride in minutes. The Green rides are ridden in Zone 1, the Yellow rides are ridden in Zone 2, and the Blue rides are ridden in Zone 3, but in what Zone should the red rides be ridden? To answer that question, our randonneur turns to another publication of Coach Hughes, “
Intensity Training for Cyclists” (hereafter referred to as
Intensity Training.) That book describes 6 training zones named Zone 1 through Zone 6. In addition to these six numbered Zones, it talks about 2 other zones named “Sweet Spot” and “Sprints”. Sweet Spot overlaps with the top of Zone 3 and the bottom of Zone 4 and Sprints are even more intense than Zone 6, they are a Zone 7 if you will. (This last point has confused me in the past so in some of my earlier posts I refer to Zone 6 when I should have referred to the Sprint zone, Zone 7.) The imperfect but (hopefully) useful approach I will take is to look at how long the various workouts recommended by Coach Hughes are and from that, infer how much Fatigue per minute ridden Coach Hughes thinks are produced in each zone. There are some leaps in logic required to do that, and I will take you through those. To do so will require knowing a bit more about Coach Hughes’ training plan.
Intensity Training describes a periodized training plan consisting of fairly typical divisions into Pre-Season, Base, Build, and Main Season periods. The training plan diagrammed above describes the Build period which is what I will be focusing on in this post. This book is designed to be flexible, to adjust to a variety of riders and goals. Our hypothetical randonneur has the ambition of riding a 200K brevet as fast as possible and so uses the Coach Hughes’ “Performance Rider” plan which includes rides in all 8 zones. All rides between Sweet Spot and Zone 6 are done one day of the week, on the “red” day. Sprints (Zone 7) are interspersed within other rides, on any day except for rest (no ride) or active recovery (“green,” Zone 1) days. Rides in different training zones are designed to develop different cycling abilities. Which intensities your hypothetical randonneur will ride during their weekly “red” ride will depend on what abilities they are attempting to improve. Those abilities (along with the maximum recommended total time for each workout) are as as follows:
Sweet Spot: Increase Power Longest Workout: 40 minutes
Zone 4: Increase Lactate Threshold Longest Workout: 30 minutes
Zone 5: Increase Racing Speed Longest Workout: 20 minutes
Zone 6: Increase VO2max Longest Workout: 15 minutes
Zone 7: Improve Economy Longest Workout: 2.5 minutes
When our randonneur starts doing these higher intensity workouts, Coach Hughes conventionally has them start with fewer, shorter repeats and work up to more, longer repeats. the length of the workout is (the number of repeats) x (the length in minutes of each repeat). For each zone, he has a maximum number of minutes that an athlete reaches at the end of that progression. Since these Zones are swapped in and out of the same ("red") day in the schedule, one might infer that the maximum minutes, which is different for each zone, represents the same training load. Since Load = Intensity x Minutes, one can infer the relative Intensity by dividing the constant Load by the variable Minutes (e.g. Intensity = Load/Minutes). But is it true that all of these zones have an equivalent load? Here is what Coach Hughes says:
“The harder the intensity, the more days of recovery you need between sessions. You may do two days of tempo workouts in a row if you can do a quality workout the second day. Allow at least one recovery day between sweet spot workouts and at least two days between sub-threshold, super-threshold, VO2 max and sprint workouts.” - Coach Hughes, in Intensity Training
Thus, taking Hughes at his word, it takes twice as long to recover from a Sweet Spot workout as it does from a Zone 3 workout and three times as long from Zones 4 through 7. The good news is that, by inference, the Zone 4 through 7 workouts each adds up to the same training load. The difference in recovery times between Sweet Spot (Zone 3.5, if you will) and Zone 4 is small and I will ignore it. (If I did include it, it would only increase the already large trend I am suggesting.)
What about Zones 1, 2, and 3? Zone 1 is only used for recovery rides, the goal of these rides is not to increase fatigue but to reduce it. The bad news is that means my approach cannot be used to estimate the fatigue generated by Zone 1 recovery rides. The good news is that there is no need to to do so, Zone 1 rides can be ignored as a source of fatigue.
The Zone 3 ("blue") ride occupies a different slot in Coach Hughes training plan than the higher intensity ("red") rides so there is no reason to expect that it will generate the same amount of Fatigue as they do. The one clue we have is Coach Hughes statement that Zone 3 rides can be ridden two days in a row whereas the higher intensity rides require two to three days recovery between them. From that, we might conclude that the higher intensity ("red") rides generate two to three times the total fatigue as the Zone 3 ("blue") ride. The longest Zone 3 ride, both in Distance Cycling and in Intensity Training, is 90 minutes. If I were to argue that these 90 minutes generated only half the fatigue as the 40 minutes of total Sweet Spot (Zone 3.5, "red") ride, then I would have to conclude that the Intensity (Fatigue per Minute) of the Sweet Spot ride was 90 divided by 40 time 2 = 4.5 times as that of the Zone 3 ride. Compare this to the conventional TRIMP estimates that they are at most 1.25 times greater. At this point, I want to reiterate that I am aware of how tentative my argument is. I feel very strongly that the conventional TRIMP estimates significantly underestimate the Intensity of higher intensity rides but am much less sure exactly how much they do so. Thus, to be conservative, I am ignoring the two-fold multiplier and suggesting that a Sweet Spot ride has 2.25 times the Intensity as a Zone 3 ride.
The weakest link in my argument concerns the relative Intensity of Zone 2 (long, "yellow") rides and the higher Intensity rides. Again, they occupy a separate spot in Coach Hughes training plan so there is no basis for assuming they generate the same amount of Fatigue as the higher Intensity rides. I don’t know how to fix that so won’t try; for no good reason, I will assume that the long (“yellow”) ride generates the same amount of total Fatigue (Intensity x Time) as the Zone 3 (“blue”) and higher intensity (“red”) rides. The longest Zone 2 training ride Hughes recommends is 210 minutes.
The intensity I am calculating is relative. For convenience, I set the intensity of a Zone 2 ride equal to 1* and for each of the higher zones, the intensity given is how much harder that ride is per minute than a Zone 2 ride. Thus, for each zone, I calculate the intensity as the length of the longest ride at that intensity divided by the length of the longest Zone 2 ride and this is the results of that calculation:
In the first column is the training zone number. I have never seen a case where rides in Zone 1 are used to build fitness, and as noted above, this means I will not be using Zone 1 in my estimation, it will start with Zone 2. In the next column, I have given the relative Intensity implied by the recommendation that training load (which by definition equals Time multiplied by Intensity) be determined by multiplying ride time by zone number. It is useful to arbitrarily set Zone 2 to have an Intensity of 1 and thus Zone 4 will have a relative intensity of 2 and so on. That implied intensity is given in the next column, Zone Intensity. In the third column, named Hughes Minutes is the maximum number of total minutes in a workout (day) Coach Hughes suggests for each zone. Using my logic, I then convert this into a relative implied Intensity by arbitrarily setting Zone 2 to an intensity of 1 and then multiplying that by the ratio of minutes in Zone 2 / minutes in the Zone. Thus, for Zone 4, Hughes recommends a maximum of 30 minutes. In his overall training plan to prepare for a 200 kilometer long ride, he suggests a maximum ride length of Zone 2 rides of 400 minutes. 400 divided by 30 gives an intensity relative to Zone 2 of 13.3, much higher than the zone-number based estimate of 2. In a previous post, I used the data from Gillen et al. to do a similar estimate, and, for comparative purposes, that is shown in the final column. Gillen et al. only looked at Zone 2 and Zone 7 and so I put n.d. In the remaining positions of the table to indicate that the value was Not Determined.
Am I guilty of the straw-man fallacy? Does anyone actually estimate ride load by multiplying zone number times minutes? Every single scientific paper I have read that considers ride intensity uses one of the common versions of TRIMP to estimate that intensity. In a perfect world, those papers would have justified use of that metric, but in my opinion, they do not. Some studies do go as far as to show that TRIMP scores are going in the right direction and are better than nothing, points I do not dispute, but then go on to use them in a way that relies on them being quantitatively accurate which has not been demonstrated and which I believe is
not true. As just one example, consider the publication,
Vermeire et al. I reviewed about a year ago. That publication concluded that polarization of training was more important than training volume because they found that improvements in performance correlated with degree of polarization but not with TRIMP scores. (They looked at Banister, Edwards, Lucia, and individualized TRIMP.) Perhaps there would have been a correlation with TRIMP scores had they used a more quantitatively correct version of TRIMP.
In contrast, coaches give TRIMP very little if any attention. Rather, they provide concrete training suggestions, how long an intense effort should last (20 seconds, 1 minute, 10 minutes...) and how many times that effort should be repeated. What I am arguing for is to connect the scientific community with the wisdom of coaches. This is an approach that Dr. Seiler (father of periodized training) has adopted. He argues that laboratory studies are limited in what information they can provide and thus need to be supplemented with studies of the training approaches used by successful athletes and their coaches.
If I were reviewing this post, my biggest complaint would be the lack of any experimental evidence that my approach is helpful. My response is to concede the point but then to note that this post is not intended as proof for anything but rather as a reality check and suggestion for future research. If the actual recommendations of coaches (the recommendations of Coach Hughes I used in this post are pretty typical) do not match the TRIMP protocols we are using, should we not worry about that? In short, I think coaches do not need improvements to TRIMP but rather can provide suggestions as to how to improve it. Exercise research scientists, on the other hand, often use TRIMP and thus would benefit from the improved versions of TRIMP that coaches can provide, based on their experience.
^ I confess that I understand individualized TRIMP least well of all of these and if you feel like you do understand it, please tell me about it in the comments.
* Because of the way Banister TRIMP is calculated, and because that calculation generates a value of 0.9 for Zone 2, a value very close to 1.0, I didn't bother to correct Banister TRIMP numbers.
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