## Friday, November 17, 2017

### IF and TSS

There's a couple metrics worth looking at after a ride and they are Intensity Factor (IF) and Training Stress Score (TSS).  I'll define each:

IF (Intensity Factor)= NP/ FTP

where: NP= Normalized Power (watts)
FTP= Functional Threshold Power (watts)

Normalized Power (NP) is an estimate of the power that you could have maintained for the same physiological "cost" if your power had been perfectly constant, such as on an ergometer, instead of variable power output.

Functional Threshold Power (FTP) is your "hour power".  That is, the maximum sustained average power for 1 hour.  This can be estimated by performing a 20 min TT and multiplying the max sustained average power for 20 min. by 95%.

Example:

I rode for 1.5 hrs. and my Normalized Power for the ride was 230w.  My FTP is 220w.  Therefore, IF= 230/220= 1.05   BTW, that's a pretty intense ride/workout.  Normally, tough workouts are around the 0.75-0.85 mark.  When I see an IF over 1.0 I'm suspect of the NP or FTP, or both.  I think in this example, the NP was too high since I know my FTP is definitely 220w.

TSS (Training Stress Score)= can be manually calculated or determined by an algorithm inside your bike computer or software that looks at the power zones you ride and time you ride in those zones.

Example:

My ride consisted of 30 minutes in L2 Zone, 1.5 hr. in L3 Zone and 1 hr. in L4 Zone.
By definition, an TSS of 100 is equal to riding at your FTP for one hour.

L2 (1.3 weight factor) x 30 min= 40 points
L3 (1.5 weight factor) x 90 min= 135 points
L4 (1.7 weight factor) x 60 min= 100 points

Training Stress Score (TSS)= 275 points  BTW, that's a pretty hard ride/workout for 3 hrs.  And, that's NOT the exact weighting factor that's used to compute TSS but you get the idea.

Power ON!  Coach Rob