Alex Thompson Blog: Functional Threshold Power

  • By Alex Thompson
  • Published March 6, 2013

FTP (Functional Threshold Power): the magic training intensity, or something to be treated with caution?

This post was the result of a comment on my Facebook page. This is a really interesting subject for me and thought it was worth taking the time to answer this point fully, I hope you guys find it useful. This is the comment which got me thinking ‘after all the higher your threshold the faster you will go’. In other words if I trained at 25 mile time trial race pace would it help my Ironman time?

Threshold or which I will now refer to as FTP can only be a certain % of VO2max, while in turn VO2max is limited by the amount of muscle fibres you have which can use oxygen as fuel. there is no point in trying to raise FTP if your VO2 isn’t high enough. In other words make sure you have the right engine before you start tuning it up. So how do you know if you’ve got the right engine?

I got a dexa scan (it measures muscle fat bone and organ mass) and Alan Couzens gave me a rough ball park figure of the weight I needed to be. He looked at what the best Ironman athletes in the world looked like through a dexa scan and told me what I needed to do to get to into that sort of shape. He looked at their peak power and VO2max, and we worked on that. When satisfied that we had enough muscle to work with we set out turning that muscle mass in to slow twitch muscle mass, as that is the muscle fibres that are used in Ironman racing at all levels. The way to do that is to stimulate the IIa (the ones which are fast twitch but use oxygen and carbs as fuel rather than oxygen and fat like the slow twitch) to turn more slow twitchy. We have more than enough fat for an Ironman but a limited amount of carbs we can digest and store in our bodies, so the more energy from fat we can use the faster we can go. This is done by going just hard enough to trigger the IIa fibres a little but do it over a long period, encouraging them to change. How do you know enough is enough?

You look at a lactate graph, fast twitch fibres release lactate which is OK, but the more watts you can produce before you have to recruit them shows how much slow twitch you have. Even if you can produce 380 watts for an hour it doesn’t mean a thing if can’t produce a lot of watts from fat. Much in the same way that many good marathon runners can’t produce anywhere near that performance on race day as they have just burnt through all their fuel.

As all intensities fall on the lactate curve, we can see the whole picture. The shape of the lactate curve indicates what type of athlete you are. An elite 400m runner will produce orders of magnitude more lactate at peak than an elite Ironman as they have more fast twitch. Conversely a world class marathon runner would struggle to produce more than 6mmol of lactate at peak as they are more slow twitchy. It’s all about the muscle fibres used for the event and the energy sources to supply them. Elite Ironman athletes race at 1.2-1.8mmol of lactate above base line, not easy but way below the 4mmol where FTP sits around.

For people at the front of the field the game is to see how many watts you can push while only producing that level of lactate. How do you train for an event which lasts (generally) over 8 hours? And is FTP training the best way of doing it? Does raising the amount of watts you can produce at 4mmol drag up the watts you can hold at Ironman pace? What does this training look like and how much can an athlete tolerate, would total load suffer as a result of high intensity training, if so does total load (above AeT) effect Ironman performance?

Lets talk turkey, before we discuss the value of this workout compared to others, lets look at what different work outs look like and their effect on the body, particularly in terms of training stress.

A couple of weeks ago I did a solid long ride. My threshold was 270 and I went for the best part of six hours and average over 213 watts (NP) that is a solid work out, in fact my heart rate was the same as most of my Ironman bike splits. That is one big training and 340TSS (TSS = Training Stress Score)! A classic threshold workout is 2×20” @FTP that’s 66TSS plus warm up cool down etc so to be generous we’ll call it a 100TSS work out. What is the effect of that work out on recovery, the first one I matched glycogen expenditure over the course of the day, took an easy day (80TSS) after that and went for a 250TSS ride the day after at a similar intensity, if a little higher.

With the FTP workout only being a third of the training stress could I complete 200 or so TSS in other ways? 50TSS in the pool, would be a very solid work out which would as mean I’d need a 150TSS run, I couldn’t do much at threshold as my glycogen stores would be depleted from the bike work out so I’d have to run steady which would mean roughly a 2 hour run still at a fair clip. That is an insanely hard day for the same TSS and likely to cause injury so we’d have to conclude that FTP work would lead to lower overall weekly TSS.

Is weekly TSS a factor in fitness? Yes. Cycling is a sport which has been around for a long time and the level of performance has been high for a long time, tonnes of people have been riding 55 minute 25 mile time trial bikes on road bikes for decades. This has been done largely on a training dose of winter base miles leading to threshold work later in the year. In elite runners Lydiard got middle distance runners to run huge volumes in the off season before working on speed and to much success (Olympic medals is a good sign of success in middle distamce running). The weekly mileage marathon runners setting world records has been going up with every new record. Doing more work to gets better results, this is why recovery is so important, to facilitate more work. So I’d argue that weekly TSS is a big factor in performance.

Is all TSS created equal or is it just a question of doing the right amount of anything? Are there particular work outs which lead to better results, is there a magic work out? There is no magic workout it is just work. However different workouts have different impacts and you should change training throughout the year.

In respect to FTP It also links into the trainability and sustainability of different qualities. You cannot increase FTP forever, there comes a point of diminishing returns, also after raising it you have to sustain it. A general rule of thumb is that FTP work leads to FTP improvement for around 2 months after which point it platues and you have to maintain it. That is why cyclists talk about winter base miles.

So why is the best time to work on FTP? Is it worth it?

It depends if you are time limited and you are filling all those hours and it feels easy, then throw in some higher intensity it would lead to a higher weekly TSS after you’ve laid a solid base. If you look at the graphs in the soon to be classic textbook training and racing with a power meter and your FTP number is only a 4th cat while everything else it 2nd cat then go for it. A great rule of thumb my coach has quoted on his blog is that peak watts should be 4x that of your 2.5 hour power, if not work on building muscle and strength, if your peak exceeds your endurance work on your endurance. In my experience of being in the triathlon game for a while now most people would benefit from more riding.

Let it be said again that steady state training isn’t easy, easy riding is easy and that does little to develop athletic ability. Lots of miles at a decent pace is what it’s about for Ironman.

You can get more information about Alex on his Facebook page or on Twitter: XIronmanAlexX

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