.If, KJS and TSS

Is there any correlation between the .IF and KJS you burn over an hour period. I’ve been looking at my kjs burnt and .IF and found its pretty close .60If will be around 600kjs. And TSS will be around 60 as well.

Maybes I’ve missed this in a Podcast I cant recall a similar discussion.

TSS is based on IF and time so those relate. 1hr at 100% FTP=100TSS.

IF and kJ aren’t related. KJ is all about watts. As your power increases you’ll put out more kJ. It’s a power based metric. 100w will get you 360kj/hr

Basically, as you get stronger you burn more kJ at lower IF and less TSS because your watts at a given intensity increases as your FTP does.


I’m not so sure that is correct. In fact I’m pretty sure it’s not.

1hr at precisely your set FTP = an IF of 1.

Does an IF of 1 always mean a TSS of 100? I’d suggest not because TSS (by design) can be accumulated in various ways… long/slow or short/fast (both of which will result in wildly different IF’s).

As to Kj… this is simply a (precise) measurement of exactly how much energy you’ve put into the bike. It is unfiltered, raw data as measured by your power meter. The other metrics being discussed are all “processed” based on whatever has been set as ones “FTP”.

Now a discussion on what FTP is, and what it is not, has been done to death. Hint: 99% of people are wrong on this, too.

From Training Peaks…

A kJ is literally 1000J. A Joule is a metric of wattage and time…

“Rule of thumb” and a very rudimentary one at that.

Fact: 100TSS may be accumulated in 1 hour, if riding at exactly “FTP” (an IF of 1).

Fact: 100TSS may also be accumulated in, say, 3 hours at a super low IF…

And everythign in between.

100TSS can be accumulated in hundreds of different ways.

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That’s effing hilarious - TP doesn’t even understand how their own trademarked metric is calculated!


So can an IF of 1.0


True, but it’s less likely.

If you ride long enough, you’ll eventually hit 100TSS.

You’ve gotta ride from the outset at “FTP” to get close to to an IF of 1… and the longer you’re below “FTP” at the beginning of your ride, the higher above “FTP” you’ve gotta go (and for longer) to get back up to an IF of 1.

Wow. That from TP is completely wrong. TSS is based on IF-squared. TSS = IF-squared x time in hours x 100.

30 minutes at .6 IF is 18TSS and not 30.

IF uses NP and not AP so it is definitely possible to have a 1 hour ride over 100tss and an IF greater than 1.0.