Normalised Power, TSS, CTL and other Training Peaks terminology 🤓
When you get a power meter there is a quite a lot of new terminology to learn. This may seem unnecessarily complicated, but these concepts all help you think more critically about how you are riding.
It will also help you join in the conversation at the café stop if things get technical…
FTP: Functional Threshold Power
This is how the maximum power in watts that you can sustain for a prolonged period of time. Most of the time when people talk about FTP they mean the average power you can gold for an hour, when you are fully rested and in a race situation. A more accurate term is “60 minute critical power” or CP60 but most people just call it FTP.
A 25 mile time trial is the perfect way to measure this, as this will be around and hour and it was a race situation so you’ll have gone full gas.
The classic way of measuring your FTP on the turbo trainer is a 20 minute test which involves smashing it as hard as you can for 20 mins, then taking the average power you achieved and subtracting 5% (i.e. multiply by 0.95) to give an estimate of what you could do for an hour. However, due to the fact that it’s harder to motivate yourself on a stationary trainer, and that most people aren’t able to produce as much power on the turbo (due to overheating, not being able to throw the bike around etc) it’s becoming normal just to take the 20 minute figure as your FTP.
NP: Normalised Power
This is quite commonly misunderstood, but it’s a simple concept.
Doing 1 minute at 400w followed by 1 minute at 100w repeatedly gives an average power (AP) of 250w. However, doing those intervals repeatedly for 30 minutes is much harder than doing 250w steady for 30 minutes.
Normalised power addresses this, and tells you what the ride “felt like”. A session will usually have a much higher normalised power (NP) than the average power (AP). NP is what is used to calculate IF and TSS (see below).
IF: Intensity Factor
This is the fraction of your FTP (or FTHR) that you did during an activity. It’s expressed as a decimal but you can mentally multiply by 100 and it becomes a percentage.
For me, a typical hour long ride with a few hills like the one pictured above will show as about 0.83 IF on Training Peaks. I wasn’t doing anything specific during this ride, just riding how fast I felt like going that day.
The 0.83 IF means my normalised power for the ride was 83% of my FTP.
My FTP is 285w at the moment. So 285 Ă— 0.83 = 237w which you can see is the NP shown above.
Longer rides will typically have a lower IF. For example if I do a 3 hour ride then the IF will usually be in the region of 0.77
TSS: Training Stress Score
It’s simple to think of this as your normalised power multiplied by the duration of the ride. The actual formula is IF² × hours × 100 but you don’t really need to worry about that.
The main thing to know here is that the maximum TSS you can get for an hour’s riding is 100 — that would be a full gas race level effort. Typically when you’re riding though you’ll get about 60–80 TSS per hour unless you are doing a really hard session.
If you ride longer or ride harder, you will generate more TSS.
CTL: Chronic Training Load
This is the average TSS you do per day. It’s actually a very clever weighted average, so the training you’ve done more recently has a much higher impact on your CTL than the training you did several week ago.
In theory even training you did years ago impacts your CTL, but the impact is so small it will be dwarfed by your more recent training.
I find it useful to think of your CTL as the average daily TSS for the last 6 weeks. Because of this, if you’re new to Training Peaks it will take about 6 weeks of data before you get an accurate CTL figure.
As an example, say you tend to work in blocks of 4 weeks like a lot of people. For weeks 1–3 you do 600 TSS per week, and week 4 you do 300 TSS as a recovery week. That gives an average of 525 TSS per week.
Divide your average weekly TSS by 7 and that gives you your CTL. In this case 525 TSS per week gives 75 CTL.
TSB: Training Stress Balance
Last acronym! This is quite complicated mathematically, but all you need to know is that it’s an indication of how well rested you are.
A negative TSB means you are training hard and pushing your CTL up.
A positive TSB means you are “fresh” and ready to perform well in a race, or you might be in a recovery or rest period. As a result your CTL will be going down.
For me, if my TSB goes below about -30 then there is a serious chance I’m going to get ill. Some people can handle more training fatigue than this, some people less.
Fortunately the ATP (annual training plan) can help you manipulate your TSB and be on perfect form for races 👌. Blog post about this coming soon…
