Power Based Impulse-Response Performance Model

I hope everyone is enjoying the Tour de France and PEZ’s unique coverage as much as I am. With the Alps and Pyrenees behind us, it is quite evident which riders had form, lost their form, or found their form. Let’s take a closer look at what the commonly used cycling term “form” exactly is.

Daniel Coyle describes “form” in "Lance Armstrong’s War" as “one of the more mysterious elements of bike racing, possessing an otherness that is revealed in its preposition… referring to the elusive moment when all systems are working at optimum efficiency”.

The etymology of “form” goes back to eighteenth century horse racing where sheets would be passed out to the betters detailing the past performances of each horse. Doesn’t that sound familiar to the media speculation from the race results of the Dauphine and Tour de Suisse? I think so.

For the athletes, coaches and directeur sportifs “in the know” Tour de France form is a known quantity and not mysterious at all. In fact, it is a closely guarded secret from the competition and consequently the media. Form is the result of a strategically selected race schedule, and a carefully managed training plan leading into the Tour*. 

What is "Form"?

In cycling the word "form" describes a combination of physiological & psychological qualities that enable peak athletic performance(s). Form is power output. Form is “going good” when you want to go good. Form is having a ton of matches to burn in a race. Form is feeling like you can rip the cranks off the bike. For those athletes racing** with their powermeter, form may be measured with an all time high peak power output. Or simply, it may be setting a PR up your favorite climb.

It is important to recognize that cyclists will not always be on form or may even ever have it. Athletes must first “go big” with their training before they have the chance to decrease their volume and elicit form. Scientifically, form is just the right balance between exercise induced physiological adaptations and the time required to optimize those changes. An even geekier definition is a positive impulse-response relationship: a value calculated by the amount of training you’ve done and the recovery you’ve taken.

A Predictive Performance Model

You may be familiar with the heart-rate based (TRIMPS) model developed by Dr. Eric Bannister in the mid 1970’s and popularized by triathletes in the nineties. Bannister’s model uses raw heart rate data to understand how training affects athletic performance. In essence, how much to train and when to rest in order to achieve the ultimate form.

In the 1990’s French physiologists, Thierry Busso and his colleagues took Bannister’s TRIMPS model a step further. They developed an impulse-response algorithm to show the relationship between the positive gains from training adaptations and the negative gains from fatigue. Busso’s lab crudely calculated the training impulse by multiplying the number of intervals performed by their intensity. These training units were entered into the algorithm to calculate the response. To validate the model, laboratory based performance tests were shown to match the response predicted by the model.

Since Busso’s work, the raw data accumulated from downloading daily powermeter files has become the ultimate measure of an athlete’s daily training impulse. Dr. Andy Coggan’s metric, training stress score (TSS), enables us capitalize on Bannister’s and Busso’s original work with a power-based performance model. When it comes to training with power, this separates the men from the boys. As Lance likes to describe his F-One equipment, this is the “Shit That Will Kill Them”***.

Lance, bro, when you are done with number seven, send me your files leading up to the Tour and we’ll model out your performance. Have your people contact my people.

Proof of Concept

In the meantime, here is how the model looks in the Performance Manager Chart. Over the past 16 years, I've successfully used the model to predict and plan peak performances for hundreds of athletes. This model helps coaches and athletes prepare, plan, taper and most importantly peak for A events. 

In the figure above, the positive gain from training is defined as Chronic Training Load or CTL. Acute Training Load or ATL reflects short term fatigue. Form, a.k.a. Training Stress Balance a.k.a. the response is calculated in the algorithm from CTL & ATL.

The number one take home point from the graphic above is that the yellow trace (TSB) was at its highest for my goal events. I used the model to manage my training for the greatest TSB and consequently my best race results in the month of June.

As the saying goes, a picture is worth a thousands words and I couldn’t agree more and then some. In my next Toolbox I’ll elaborate on this model further and discuss the principles of training behind it. Until then, good luck with your form and enjoy the rest of the Tour de France!


Banister, E.W.; Calvert, T.W.; Savage, M.V.; and Bach, T.M. “A systems model of training for athletic performance.” Aust. J. Sports Med 7:57-61, 1975

Busso, T.; Benoit, H.; Bonnefoy, R.; Feasson, L.; and Lacour, J.R. “Effects of training frequency on the dynamics of performance response to a single training bout.” J Appl Physiol 92: 572-580, 2002

Busso, T.; Denis D.; Bonnefoy, R.; Geyssant, A.; and Lacour, J.R. “Modeling of adaptations to physical training by using a recursive least squares algorithm.” J Appl Physiol 82: 1685-1693, 1997

* Sprinters will adjust their form to be optimal for the first part of the Tour while the GC contenders will use the initial flat stages to taper down into their peak form for the upcoming mountains

** I distinguish between racing and training because nine times out of ten, athletes see their personal best peak power outputs in races compared to their training. The extra adrenaline and motivation associated with competition bring outs the best data. That’s not to say you won’t generate great evidence of form in your training, you will if you or your coach is tracking your training data.

***from Daniel Coyle’s "Lance Armstrong’s War", HarperCollins, 2005

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Frank Overton 7/19/05 Frank is a full time professional USA cycling Expert certified coach, and category 1 road racer. He earns a living eliciting peak form from his athletes around their most important races. 

About Frank Overton

Frank founded FasCat Coaching in 2002 and has been a full time cycling coach since 2004. His educational background includes a Masters degree in Physiology from North Carolina State University, pre-med from Hampden-Sydney College. Frank raced at a professional level on the road and mountain bike and currently competes as a "masters" level gravel and cyclocrosser. Professionally Frank comes from medical school spinal cord research and molecular biotechnology. However, to this day it is a dream come true for Frank to be able to help cyclists as a coach.

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