TSS vs IF - Right Approach?

hi there,

Due to some family priorities I had to shift my workouts from evening to morning. At the same time, I have to be at work by 0730hrs.

So this led me limiting my workouts to 60min only. So wake up at 5AM, get on the trainer at 0530, finish workout at 0630 and shower, breakfast etc and be in the office by 0730hrs. My office is only 15 minutes drive from my house so this is doable.

Here is my question, by reducing the workout’s duration, I am losing quite some TSS.
However I am selecting workout’s variant with high IF. For example I had Kaiser+4 with 122TSS and 0.85IF and I replaced it with Kasier +1 with 87 TSS and .93 IF. While this keeps gained TSS low, I am raising the intensity of the workout.

As it is 40% how long you ride and 60% how hard you ride, I would like to hear your opinions :slight_smile:


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I’m not sure where that 60/40 breakdown comes from, but with regard to such short duration workouts.

What phase are you in? Base? Build? During Base, TSS would be more important than IF – doing more tempo/sweet spot in those sessions would help elicit some aerobic adaptations. Someone will bring up Seiler and the study on Portugese runners with limited training time. I would respond that it was a 12-week study, not a season-long one. Many high-level masters have taken the “1 hour of sweet spot” approach during the week, and a couple of LSD rides on the weekend, to build a fast base – Kevin Metcalfe, for example. He shared that his base training was mostly 1 hr rides at 85% FTP, then a pair of 4-5 hour rides on Sat-Sun.

If Build, ok, that’s where polarized comes in, and IF will be more important on your hard days. Something like one VO2 or AC interval session during the week, everything else just zone 2, a ride on the weekend that accumulates 15-20min of high intensity in 1-8 min chunks, and a long LSD ride if you can.

Either way, it’s about limiting your losses. The reduction in volume will result in a loss of fitness eventually. But, increasing TSS during Base, and making sure you get a whopping VI and IF on the hard interval days during Build, will use the time effectively.

If you’re a TR user, then just stick with the low-volume plan for whatever phase you’re in. Coach Chad has your back.


Don’t always be fooled by the IF of a 90 minute workout like Kaiser +4. It’s actually very intense, with 6x3min @ 122%. It’s just the extra endurance interval tacked on the end that brings the IF down to .85.

However - in this specific case I wouldn’t recommend Kaiser +1. It has a high failure rate, and no wonder, as it only allows 3min rests between the 3min intervals @ 122%. That’s tough. Very tough. I’m not surprised it isn’t in any current training plans.

So if you can squeeze another 15 minutes on a Thursday and do 75 minutes, I’d agree with @RobertK. Unless you have time to analyse each workout variant, you’re better off just going to the low volume plan. Where you’ll see Coach Chad has given you Kaiser +2, which despite being +2, is actually more do-able than the +1 you were thinking of.

If you really only have 60 minutes, then I’d have done something like Spencer +2. But going forward, you may need to spend a little more time researching workouts to find the right 60 minute one.

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hi, thank you for the responses.

I am in last week of General Build Mid Volume and starting Rolling Road Race Mid Volume from next week.

Regarding 40/60 ratio, i remember reading it Joe Friel’s book and requires double checking. I may be wrong but he was comparing intensity of the workout. But as said, maybe I am mistaken. I will check this evening.

And regarding Kaiser+1, you are absolutely right, it is damn it is hard.

Another wrinkle – look at VI for the whole workout, IF for the interval selection.

Say you do 5 x 4 min VO2 intervals. If you’re fresh and you’ve really nailed them, the IF for the highlighted section of the 5 intervals and the 4 rest intervals between them should be .98-1.0, the NP at FTP or within say 5-10w.

As a result, that workout will probably have a VI of 1.2 or higher. So the IF for the whole workout may only be .8, but when the whip came down, that IF was much, much higher. The high VI will tell you that.

Quality Build workouts have high VI, and a high IF for the interval sets.


Just checked on TP as you said :slight_smile: and guess what?
VI 1.2 and IF 0.95 for the given intervals :slight_smile: Good one :clap::clap::clap:.

and NP is 15w below FTP

My other question will be then what the realtion of VI with this topic is? As far as I know VI shows how smooth is your pedaling.

TSS isn’t a goal, it’s a metric that may or may not having any bearing on your training. The goal isn’t to ‘drive up TSS’ beyond that TSS tends to go up as you progress.

If you only have an hour to train per day then you’re going to need to be doing tons of VO2 and threshold work to get any type of gains, and you’ll quickly run out of room in the threshold workouts to progress any further.


Variability Index (VI) is the ratio of Normalize Power to Average Power. If you hold the same wattage for the entire workout then your VI is 1. If you are doing VO2max, PMax intervals, or whatever, your VI will be higher.

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Variability Index is a measure of the stochastic variation in the workout – so, not so much how smooth you were pedaling, but what was the difference between your hard pedaling and soft pedaling in a workout or race.

Say you are pedaling at 700w for :30, then resting at 150w for 2-minute recoveries in between. Your VI is probably going over 1.3 – which tells you that your hard was stonking hard, and your easy was slothfully easy (which is what you’d need to do to really max out those :30 punches).

The lower the VI, the more evenly paced the whole workout/race was. A hilly 45min criterium? VI of 1.35, for example. Bike section of an Ironman? VI of 1.0.

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Thank you so much. Really tons of good information. Appreciated

Some additional comments re: VI and IF:

V.I. for an entire workout is similar to I.F. for an entire workout - unless you dive into the details, it doesn’t tell you much.

V.I. for a single hill climb or flat segment is a great indicator of pedaling (actually power delivery) consistency. 1.07 is recreational 1.05 is good. 1.02 is excellent. 1.002 is elite. While I have done 1.002 on a PR hill climb effort (lots of training to do so), I recently did a 12kft century and accomplished 1.02 on the 3 hill climbs. However, my VI for the 102mi/12kft ride was 1.32. Is the 1.32 useful info?

I.F. is subject to similar issues as V.I. in that it’s really the details that matter. It is possible to compare two similar workouts, but relatively small changes can effect it, such as amount of time during warmup, rest intervals, and cool down. If you want a deeper dive understanding, I would suggest importing a couple of workouts into WorkoutCreator, make some changes to these 3 parameters (WU, RI and CD) and see for yourself.

To @Thebigred original question:

On a limited schedule, I would focus on Time-in-Zone (rather than TSS or IF). While WKO software provides the reports to track this automatically, if you aren’t a WKO user, you can use a spreadsheet. Simply track the amount of time you are spending in the various training zones you are training in (sweet spot, threshold, lactate clearing, VO2) to make sure you are meeting your goals (whether maintenance, increasing your fatigue resistance or growing your VO2Max).


Use the weekday rides to build those, anaerobic engine, very specific drills and the weekend do the longer endurance rides and you will be fine.

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Like all training/power analysis questions, the answer is yes and no.

In the OP, the question was whether to focus on VI or IF to measure the “quality” of short, 1 hour workouts. The answer is “it depends.” Are you using low VI and moderate IF to build base on short duration (a steady hour of tempo, for example)? Or are you doing VO2 max intervals?

Of course, IF and VI have to be seen together – their relationship is what gives one a much better picture. If I did 2 hour ride with an IF of .55 and a VI of 1.3, then I spent a considerable time farting around and coasting, and the hard parts were not particularly hard, but too hard to be recovery – so it was neither an endurance ride nor a recovery ride, and it’s hard to see what the point of that session was.

An hour with an IF of .5 and a VI of 1.0? That would be a productive, well-done recovery ride.

Two hours at IF or .85 and a VI of 1.3? That would be a pretty fatiguing interval/fartlek ride, with a substantial amount of time in zone 5 and higher.

But yes, in regard to the OP – unless you’ve been using powermeters for a long time and know what your body responds to, how to train and how to rest, just follow one of Coach Chad’s plans. They work.


You don’t have to use a spreadsheet or spend money. My site Intervals.icu tracks time in zones. Your rides need to be on Strava.


Cool site!

One more power-based chart and graph time sink. I like it.


I believe I understand all of your points. However, what I am suggesting to the OP, is that neither TSS nor I.F. should be the focus of the decision process for an hour workout or less. Both are interesting side information, but the primary criteria would be accumulating time spent in zone for what the OP is trying to achieve, whether sweet spot, threshold, lactate clearing or VO2Max intervals, such as 20mins of the 4x5 VO2s you mention above.

FWIW: I.F. does become interesting and useful as a measure of fatigue resistance on multi-hour rides. For example, through fatigue resistance training, I increased my Stamina (a measure of the PDC tail) into the mid-80s, such that, on that 12kft century I mentioned above my 7hour I.F. was at 0.76, an all time high for that length of a ride. Generally speaking, I find I.F. most useful [post ride] for high variability outdoor rides, such as group rides as short as 90mins to as long as centuries.

This. When volume suffers, time in upper intensity zones (say 90% of threshold on up) becomes the primary thing.

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