What is fitness?

So in layman’s terms what does it mean or how is it defined?

From listening to the podcasts or reading the blogs I assumed it was some measure related to your aerobic threshold or something .

Yesterday I found a tr blog article that referenced ctl as fitness which is basically your 6 week rolling average .

So that being said, it would seem that all things being equal I’d have the same level
Of fitness whether I did all endurance level rides to get my tss or all threshold workouts. That doesn’t seem right to me, as such I assume I don’t truly understand what fitness is, or if I am right, what value do I have in tracking average tss irrespective of intensity?

Great question, and one that I probably won’t answer well, but here goes.

All TSS is not created equal, as they say. What that means is that you can hit 100 TSS (or a CTL 6-6-week avg) in different ways. You can do all “hard” stuff all shorter intervals. You can do all “easy” stuff at longer intervals.

The end results is that some aspects of your abilities will improve with either methid. But there will ask be some notable differences. Meaning one will make you more capable in high intensity up to all point, while the other will lead towards better long day performance.

As with so many things in this realm, the answer to what fitness is “it depends”. We can gather info from the TSS, FTP tests, power profile tests and other methods. They all measure different things and tell different stories. It’s not entirely possible to test 2 individuals with the same test and entirely predict performance capacity.

We get into things for events like all the preparation, mental state, race craft and other variables that dictate actual performance on a given day or event.

As to how to use the TSS and CTL, others will have better direct answers. But it is something to track for trends on your body (stress applied) and then considering how those workouts or events feel. Look at increases or decreases in CTL relative to your performance and overall fatigue. It may help identify when you need to work in and break or take it easy. Or can help you plan for and set a peak to meet a particular event.


Thanks chad!

And yes I have heard that comment re:not all tss being equal. That’s why I’m confused a bit bc I’m not sure how to track if I’m getting more “fit”. I can go on feel but I tend to like to track numbers and while 6 week average tss load (the existing fitness measure ) is one piece, as is ftp, outside ride speed , and maybe trending specific workouts over time it seems incomplete or subjective .

Perhaps my better question is, what should I track to determine if my aerobic base is getting any better? I believe this is my major weakness, or so I believe given how easily I go anaerobic and gas out on outside rides.

I’m doing a round of traditional base low volume bc I have time in my calendar and it works better bc I’m coming into this with some minor injuries and want to build intensity after I get some time in the saddle and my consistency up. Also I’m training for a half Ironman a year out.

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In laymen’s terms fitness is the ability to go deeper and longer more times than before.

CTL is a moving average of the last 42 days TSS. Technically if your CTL is going up you are getting more fit. I have not combed through these plans as I’m new to TR but, in general any plan will systematically and incrementally increase TSS/week. Every few weeks a recovery week allows rest and adaptation. The next block will bump up the TSS again etc…and CTL rises.

What all this translates to are many many things and depends on the riders history, genetics, determination etc…Subjectively a few examples might be:

-Having the ability to hold 235W for 3 hours v. 2 hours.
-At the end of a long ride or race you can follow fast wheels and top it off with a strong sprint whereas before maybe you couldn’t even follow the fast wheels let alone sprint out of it.
-During a criterium or fast Tuesday night practice race you are able to stay up front and/or bridge to a break.
-Same criterium/Tuesday nighter you are able to pull through XX% harder and/or XX% more times.

Be careful chasing CTL/TSS. I’d just recommend sticking to a plan an evaluate at the completion of it. I and many friends have dug ourselves into rather deep holes thinking we could tolerate the TSS required to raise that CTL another 5 numbers. Anywho that’s why TR and other resources are so valuable. These plans are well thought out to increase fitness and then sharpen it.


Great points and good info.

One point of clarification is that I’m not trying to chase anything I’m just trying to identify what measurement best reflects fitness and what I should be tracking.

It doesn’t sound like there is anything objective bc tss doesn’t reflect type of work and isn’t always equal, and ftp only represents your one hour power.

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I use something called WKO+ to analyze my data but, TR has a timeline on top of the calendar. You can scroll over the week and see the actual TSS, planned TSS, 6 wk avg and 6 wk daily avg. The 6 wk daily average is CTL.

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Fitness for what?

Chris Hoy or Chris Froome?
Usian Bolt or Eliud Kipchoge?

Fitness is defined by your own goals and achievements which can be informed by TSS, CTL and other cycling training metrics and concepts but aren’t entirely defined by them. @KorbenDallas rightly lists several ways in which ‘fitness’ could be measured based on different cycling goals.

You say you are training for a HIM so presumably your bike fitness in this period will be defined by the power you can sustain for the time the bike leg will take.

To take a hypothetical example which you yourself allude to in your last post - you take a short test and find your FTP is 250W but know you can hold 200W for the duration that your HIM. After some training over the HIM distance you can now hold 210W for the duration but when you repeat the short test to determine your FTP (which all the other metrics are based off) because you’ve only been training over the HIM distance that number goes down slightly as you haven’t trained it. Are you fitter? If you measure based on the FTP number you’re less fit. If you base it on what you are actually training for you are objectively fitter.

This scenario is possibly unlikely as training based on a sound plan will likely see improvements at many durations even if they aren’t the specific focus of the training itself but illustrates the difficulty of relying on the algorithms of CTL and TSS. They are based on the somewhat nebulous concept of ‘FTP’ - a metric which can mean the power you can hold for somewhere between 40 minutes to over an hour which we as cyclists distill into a single, precise number based on a one test, at one moment in time often over a different duration than the one it’s supposed to represent.

One way of achieving this is to track power at different durations over time. As you’re training for a HIM you could create a chart (I use Golden Cheetah for analysis but there are many others and you can easily create a simple spreadsheet) tracking 30m, 1h, 90m, 2hr and 3hr power. Use a trendline and if the numbers that you are particularly concerned with trend upwards you are objectively getting fitter for the event you are training for.

Chances are if you follow one of TR’s plans which are based on progressive overload and increasing specificity toward your goal event this should happen anyway. If you regularly see TrainerRoad PR’s appear on some of the key workouts while following a plan you’ll be on the right track.

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‘Fitness’ generically speaking (and as I understand) is the ability to recover from any given effort.

Stamina (how hard you can go), endurance (how long you can go hard for) etc are other facets of fitness itself.

CTL, ATL, TSB are metrics which form the PMC and attempt to quantify your performance.