Is TSS of Sub-threshold Zones/Levels Created Equal?


TiZ is very useful, but not sufficient. If you watch Tim’s webinar on Fatigue Resistance, you will clearly realize that it isn’t just about spending time in the zone you are focusing on, but additionally doing the work progressively (progressive intervals: more intervals, each longer). If you do progressive intervals, then TiZ will grow.

TSS is still really important as I tried to delineate above - for overall load on the body. In addition to for individual workouts, TrainerRoad uses it by showing the progressive load differences between plans and as you go from SSB1 to SSB2, etc. The issue is that people are trying to extend its use too far.

I’ve been using WK04 for the same 3-year period that I have been using TP Premium. It is an extremely valuable and powerful tool. In the Fatigue Resistance comments above, WK04 provides Time to Exhaustion (TTE) data which tells me how much benefit I am getting from progressive intervals (i.e. pushing the PDC curve to the right). For example, when I started SSB MV1 I was at 30+mins; I pushed that to 1hr 3mins at its completion. But of course, that got hammered back down when I did my FTP test and had to raise my FTP.

The downside of WK04 is that is has a significant learning curve (i.e. you need to spend a lot of time to make good use of it). The original product is 20 years old and its not clear they have improved much in the way of the user interface. I’ve suggested to them to integrate TP Premium and WK04 into a single, user friendly product, but not clear if that is part of their product direction.

In addition to the PMC chart, I use TP Premium for its calendar and ride analysis (both much deeper than what TR provides). So it really depends on your needs and time available.


See my post/answer above. I very much get the TTE concept. I’ve been taking a “fatigue resistant”-centered approach to training lately, stolen directly from that video. I progress tempo, SS, and threshold intervals out as far as possible (until FTP changes of course, then i reset)

Almost exactly like this.

And as such, seems like TSS could be a very valuable tool for me. When you stick to sub-threshold work (for the most part), seems like it is created equal (and therefore useful). @Tanner1280 thoughts seem to suggest this as well.


That’s a great post! More, longer; but as Tim shows to go more longer, you may need to do more [slightly] shorter first.

There are, however, some small improvements you can make within SS work to get additional benefit. For example, I usually change workouts with SS 88-94-92 to 90-92-94. While it is only slight increase in workout demand, it improves the mental toughness game.


My opinion…25 TSS in the ATP-PCr v. 25 TSS in the glycolytic v. 25 TSS in the oxidative system yield different adaptations. So while the stress on the body maybe equal the adaptive stress to the body is different.


That is a very reasonable viewpoint.

However, why CTL is important for everyone is this: TrainerRoad (and other similar approaches) is focused on what Chris Carmichael (and perhaps others) call the Time Crunched Athlete - those looking for maximum gains in the least amount of time. However, as Chris describes, it comes at a significant cost (vs the traditional approach). And that is you don’t have a large endurance base (ie. when you fall off the wagon, you starting from a pretty low point). By tracking CTL over a long period, you can track your base fitness level. It’s over multiple seasons that those gains really pay off regardless of your A and B “race” goals.


I can see your point and fully agree that TR programs, even HV plans, are definitely geared toward “time crunched” athletes. I can also see that TSS would be useful as a general level of consistency throughout the year.

I’ve only started using TP again since I’ve gone off of a TR plan and into “semi-freestyle” SS/Z2 base phase of 12-14hrs/wk with the intent of driving my CTL to near 100 (pushing my luck at 38) before I build again in March to peak late May.

To your point about TR users and quick gains, you’re absolutely right. Most people wouldn’t entertain riding this much Z2/SS. It doesn’t give you the ever climbing ramp test FTP positive reinforcement or the fun top end speed you can feel. It’s honestly not practical in many instances either. The higher intensity, low volume approach is great for most people because even if you lose it quickly, it’ll come back just as fast.

My FTP hasnt gone up much vs the build I just finished in TR, but now I could actually ride at FTP for 60min and I’ve held 90% for over 90min in workouts without trying too hard. And I’m about 3kg lighter, which doesn’t hurt. This is the first time I’ve had this much time to train and I feel almost like I’ve never actually had a “real” aerobic base in the past.


@Tanner1280 It sounds like you are doing great (!) and have a great perspective.

FWIW: Last year I had a CTL of 42 in March. By August (at the start of TR), I was at 95. During that period of time, my focus was on long endurance, tempo and threshold rides (almost no above FTP work). My FTP dropped from about 252 to 218 (almost 15% drop). Sound bad? My goal was a fast century (I did 4 x 10kft GFs last summer). My 6 hour NP went from 140 to 180 (almost 30% increase and over 80% of my FTP). As a final test, I set a goal to circle Lake Tahoe in 4:30 (my prior best was about 5 hours) . . . 3hrs 59mins :slight_smile:

I think the key message is that TR is great for the time crunched athlete and additionally for improving power at the short end of the PDC curve. But it doesn’t replace the benefits of building a strong foundational endurance base.


@Tanner1280 @bobmac Thanks so much for all the input. Getting a lot out of the discussion.

@Tanner1280 So when you are not doing a “semi-freestyle” SS/Z2 base phase–in other words, in a build phase (top end intervals, etc), does that reconcile with a “driving CTL up as much as possible” training approach? This is really getting to the heart of my original question, which is why I’m pressing it. I think, in that case, all the VO2max, anaerobic, etc. muddies the TSS/CTL/ATL/TSB waters, right?


I know you are looking for @Tanner1280 response, but if of use, I’ll give you my TR experience: Since joining TR 6 months ago and doing the sweet spot, threshold and some O/U and VO2 interval work in SSB, my CTL has dropped from 95 to 80. But my FTP has gone up from the 218 I mentioned earlier to 246 currently. While I have done some outdoor riding, it shows me that (when the weather gets nice again) I need to get outdoors for more long rides if I want to maintain a large aerobic fitness base (and keep the tail of the PDC curve high).


Once I move into a build phase I won’t be increasing my CTL. In many of the TR plans it will go up, but to @tshortt point, these are time crunched plans and aren’t going to drive your CTL vey high in base phase, even on a high volume plan. You’re basically maximizing your high end potential at whatever level of aerobic fitness you bring. Probably why there’s so many forum threads about struggling with longer SS/Threshold interval workouts.

I’m currently doing a workout of 2x30min and 1x40min SS O/U at 95%/85% with 4min rest between sets with a 110% 1min effort in the middle of the rest. I add about 60-90min Z2/LowZ3 and call it a day. This is the type of workout that done 2-3 times per week on top of a lot of Z2 will build a ton of TSS and aerobic fitness. It typically ends up being close to .80 IF for 180mins and over .90 for the first two hours. No way I could have finished this multiple times per week during general build when I was working VO2.

Once I move into build I’ll be focused on quality of my VO2 and anaerobic efforts and working threshold as well. Recovering from these efforts will mean dropping hours and TSS but I’ll look to maintain CTL (roughly) before tapering for my A race. Hopefully I’ll get an FTP bump too…

I’m only planning on 6 weeks of intervals leading into the A race. It’s a stage race and the following weekend I have a B+ race and then I’ll take a mini break, smash a couple big SS weeks (rebuild CTlL) and focus on racing, intervals and maintain CTL leading into a second peak for my A- race in August.

Also should mention I’m starting racing in March with a ton of fatigue, but I don’t really care about early season crit performance. At my current fitness I can at least hang and it’ll get me back into the swing of group riding.

Long story short, I’m basically building a bigger base and cramming what TR would call Build and Specialty into a six week block. The higher end fitness comes on very quickly so I’m not worried about timing, but again referring to what @tshortt mentioned earlier, it’s easier to focus on and see gains doing high end if you’re time crunched and so works better for most.


I love how fast these kinda topics get outta hand!

My inexperienced n=1…the max TSS I could handle would be ~850/12hrs/wk for Threshold and (probably) ~1,000/15hrs/wk for SS.

Sooo…whatever that means… :man_shrugging:


So we’ve finally found a topic on which you excercise restraint;)


And that is where TSS probably falls down. The PMC uses exactly the same metric to tell you how ‘fit’ or ‘adaptively stressed’ you are (CTL) and how ‘fatigued’ or ‘stressed’ you are (ATL).



Looks like pseudoscience to me.


Do you have experience with that tactic because i wanted to do the same!


I see where you’re going, but in reality stress is stress, physiologically. Adaptation occurs during recovery, not excercise.

This is why TSB is the number that you’d manage relative to your actual fatigue that you feel on a regular basis. It’s where the management comes in on the PMC.


I’ve done similar in the past and it’s worked well, but never having thought about it much. I’ve always taken an old fashioned polarized approach and never done SS or intervals until just before early season racing started.

So far, so good though. My main goal was to pump the brakes on my fitness while building a stronger base and I’ve taken down the top end, maintained FTP and gained a ton of muscular endurance while dropping kgs.


True. However, both CTL and ATL are a function of TSS. Where I was going was more along the lines of comparing how two riders accumulate TSS; one for the kilo on the track and one for a 40k ITT. They might have similar TSS, CTL ATL and TSB’s but, will perform dissimilarly.

I have not read through each response in the thread. If someone already went over this my apologies.


@Landis Yes all correct IMO. So what about comparison of a rider to themselves? Not to belabor the point too much but your 25 TSS example is the motivation for me asking the original question. If those are all different stress/strain, how is TSS useful?

Seems like one training scenario where TSS might be a proxy for something real is what has been presented by @bobmac and @Tanner1280, which is drive CTL up with predominantly threshold and sub-threshold work.


@tshortt in general TSS is super useful during base and build to push CTL up as high as you can before you start whatever race specific interval training. A systematic rise in stress followed by rest, repeat is pretty easy to see with TSS and rising CTL. Using TSS by itself doesn’t mean much. Have to compare it to something…