Hey there,
asking myself, how to interpete fitness score. Recently broke the 100 points. Am I fit now? 
How many points do you guys have?
Scheduling a weekly load of 700 TSS shows me no gain… Is that right?
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Fitness score is based on your 42day training load and roughly your daily avg for those 6 weeks. 700TSS a week = 100 a day = Your Fitness score 
Now don’t make the mistake in thinking that you want get better with a stable Fitness score. It’s not because your fitness isn’t rising anymore, that your FTP isn’t.
Think of Fitness more as a metric that helps you plan to avoid overtraining, or to make sure you are doing enough to become fit. A fitness score of 100 is for us amateurs a very nice figure. It represents about 10-12 hours of training a week during 6 weeks.
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In agreement with @MedTechCD…
Traditionally I find, as a master’s athlete, that more isn’t always better. Maintaining a high CTL is a lot of work and doesn’t provide enough recovery for my body. I’m “fit” at 100-110, however, when I’ve maintained 120 I’m starting to feel like that my ability to perform is slipping even though my TSB is favorable. Also, fitness at 100-110 CTL doesn’t mean I’m fit to race. I need to make sure I have the right training contributing to that CTL to reach race fitness. That said, these numbers are specific to me, you could be able to carry a much higher CTL just listen to your body (how you feel, HR, HRV, Sleep, etc) and monitor your actual performance.
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I think the answer for the OP is, “it depends”. It depends on a number of factors. Yes, you will be fit, but fit for what… flats, hills, undulating or a 40Km TT, a double century, criterium and the list goes on.
TSS is a number, and is made up based on Normalised Power, Intensity Factor, your FTP and duration. To do 700 TSS per week, as MedTechCD has mentioned, it gives +/- 100 TSS/day. That can be made up made up across different types of workouts and durations. For those reading that rely on their device/software to calculate it, the formula is:
- TSS = (duration in seconds * Normalised Power * Intensity Factor) / (FTP * 3600 second in one hour) * 100
The average cyclist, according to TrainerRoad has an FTP of 257 (quoted on a podcast within the last few months); I mentioned it because they have a large database of riders with a lot of data to back it up. Let’s round it down to 250 to make for simpler calculations. Five rides, listed below, range from 1-hour (at FTP - ouch) to a 4 hour ride (at 50% of FTP - nothing difficult). They all give an approximate TSS of 100, but aren’t all equal in your fitness and progression. Short, relatively hard intervals can give 100 TSS, just as a long recovery zone ride can too.
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Thanks guys, appreciate your input 
Fitness being called fitness is my pet hate.
You gain fitness by taking recovery periods, even though recovery periods make your fitness score go down. This is a never ending conversation I have to have with my athletes.
Think of it for exactly what it is : 42 day moving average of training load.
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Thanks James,
recovery periods is a good point. My problem is, that I have to bike Mo to Friday, which means a load of about 300-400 TSS just for commuting.
You can see my load bars above. Would you recommend single off days or whole weeks?
Really down to the individual. I go for 1 day off a week (a Monday after a big weekend of training). Build TSS over 3 weeks, and take the 4th week as a lower TSS recovery week before building again.
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If I could find a better name that wouldn’t confuse people … lots of Intervals.icu users are from Strava which is a problem if it doesn’t say “fitness”.
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What should a beginner look at to determine if there is progress being made?
Well, @david, it’s not just Strava: Training Peaks uses the same language – indeed, I think that they originated it.
We may have to stick with it, thought I’d much prefer “6-week average load”, even though that omits the “exponentially weighted” bit.
BTW, I find it easier than @Gerald’s formula to calculate NP as a percentage of FTP: eg, in Gerald’s Ride D, 50. Square it = 25. That’s TSS / hour.
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Progress is best seen when you have a goal, and you can measure the outcome as you get closer to that goal. So it depends what your goal would be.
Increase average speed.
Find a course that you can repeat, and see how you compare each time your ride the course. Obviously there will be outside factors, eg. weather, that you would need to ensure are similar.
Being able to hold a certain amount of power for a given amount of time.
Everyone’s favorite hate: the FTP test. But it doesn’t have to be that, it could be any of the PPO on the Power Duration Curve.
In terms of “fitness”, the more you ride, the higher the line of the graph gets, so that alone indicates an increase, if that’s your goal (to ride more).
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Normalized Power (NP), Intensity Factor (IF), and Training Stress Score (TSS) are registered trademarks of Peaksware, LLC, so it should be calculated their way. Any other way is not TSS, so would have to be called something else.
How exponential is “exponentially weighted”? I don’t really understand where there is more weight (and where less).
If you look far into the future (past any planned workouts) on the fitness page you can see how fitness and fatigue decay.
It’s like this in code where training_load is what was done on the day being added:
let weight = Math.exp(-1 / days)
tot = tot * weight
tot += training_load * (1 - weight)
Where days is 7 for fatigue and 42 for fitness. You can see how fatigue clears quickly but fitness takes much longer to decline.
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Simply put: a load from yesterday has more impact on todays Fitness then one from 2 weeks ago and is weighted higher. So Fitness accounts for everything that has ever been done, but the influence of workouts from 6 weeks ago or older is almost none. For fatigue, it’s similar but on 7 days.
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How does your formula work?
Let s = seconds, and use NP, If and FTP as abbreviations. ^2 = squared.
You write: TSS = 100 * [s * NP * IF ] / [FTP * 3600].
But, IF = NP / FTP.
So: TSS = 100 * [s * NP * NP/FTP ] / [FTP * 3600].
= 100 * s * [NP / FTP] ^2 / 3600.
That’s for a ride of s seconds duration. For a ride of one hour, s = 3600. In other words,
TSS per hour = 100 * 3600 * [NP / FTP] ^2 / 3600 = 100 * [NP / FTP] ^2,
which is the formula I gave above, 100 * IF^2.
I suggest renaming fitness to Training Stress and using age, heart rate, wattage and time to calculate your fitness level