Question About ICU and Strava "Fitness"

Hi all,

Apologies if there’s already a topic discussing this, I had a look but couldn’t find what I was after. There’s quite a lot of talk about TSS (and CTL whatever that is) but nothing that really covered what I was after.

Anyway, I wanted to ask the hive mind two things. Firstly, do Strava/Intervals ICU/whatever your platform of choice is weigh training volume too high for their “fitness” or “load” scores, or…

How much should I focus on nailing my high intensity sessions?

For context I’m about to complete the first week of SuPBMV (supplemented Baird for the Ramp, and Raymond for Red Lake +8) and while I’m really pleased to have nailed the VO2 sessions, which I have often carried too much fatigue into to actually hit as designed, my fitness and load scores are going down.

I usually do 2-3hrs endurance riding after my three high intensity workouts, however I’ve not planned to do that during Build. Am I making a mistake?

Afaik TSS and CTL etc are proprioritary TrainingPeaks terms, so while other platforms don’t call them that, they are calculated very similar. TSS is hours × IF^2 * 100, and because it is much easier to significantly increase your hours than your IF, it will always be skewed towards volume.


I suggest Implementing the Banister Impulse-Response Model in GoldenCheetah to see the difference between the model used by Strava (Banister and Coggan) vs the one used by TP (based on CTL/ATL).

I identify the key workouts (2)for the week and those I want to hit fresh and crush them. Anything else can be trimmed back or skipped to hit the high priority stuff. Its all about how I/you feel and making sure recovery is adequate for the key sessions.

If you are rested and hitting the highest priority workouts hard and completing them to your satisfaction, I would, personally, not worry about CTL/fitness.

It is sometimes hard to tell at the time, but I would do as much as you can while still being fresh and recovered for the high intensity sessions. Probably better to be safe than sorry and cut back and slowly add some of it back in if you are feeling good.

I personally detest the term ‘fitness’. At first I thought it was misused, but it is a domain-specific term that is used correctly. I think the problem is normal people outside of that domain do not have that specific meaning of the word in mind when they talk about it. I prefer Chronic Training Load, as just from reading it one can understand that it is some kind of metric about long term training load. But it is just one (very useful) of many metrics. And the metric that doesn’t incorporate how you feel.

For me, my CTL / fitness peaks at the end of my base phase. Some people might see that chart and think I’m at my peak ‘fitness’ for the year (fuzzy definition of fitness.). But I’m not. I’m freaking tired. And when I go into a build and the workout intensities pick up, my CTL / fitness decreases, and I’m still tired because I need more recovery from the intensity. But my TSB/form will be going positive saying I should be feeling ‘fresh.’ But I’m not because the intensity smokes me and I feel more tired than the end of the base phase. I’m not saying they are not useful metrics, I track them myself, but they are a result of my training / training period and are not useful without a fuller context of my training.


This is such a good response and I can relate to so much of what you’ve said!!

I’m decidedly in the “Grey Zone” if I look on ICU, but I don’t think I would want to carry much more fatigue or I doubt I’d be able to get my HR up. I’m possibly overachieving slightly so far but I figure I’d rather maximise my time at or near VO2max. I’ll see this week if I should add some more endurance work but maybe at ~0.6 as opposed to ~0.7.

That makes sense!