That High VI'll Kill Ya

kmepham

I just found out how important it is to ride steady.  That high VI'll kill ya.

A couple of weeks ago I posted in the Race Execution forum that I'd just finished a 3-hour training ride (not a race rehearsal) and was concerned that I'd generated 202 TSS (far more than the 175 TSS target for a HIM) but only covered 51.5 miles.  Now I've done two actual race rehearsals, and both times managed to cover the full 56 miles in far less TSS, under 160 both times - yesterday's RR was 157.7 TSS for 56 miles in 2:56.  Same exact gear, same exact course, same FTP, all TSS calculated in WKO+.  So how could the TSS be so much higher for one ride than another?

Turns out VI is the culprit.  The 3-hour training ride is mostly intervals with rest periods, compared to riding steady for the race rehearsal.  I compared one of the training intervals (with rest period) with a steady race rehearsal ride over the exact same 5-mile stretch of road, in the same elapsed time, and the TSS difference is astounding:

Training Ride: Z4 12.5' (3'), NP 223 (233 interval / 125 rest), VI 1.05, TSS 23.6

Race Rehearsal: 15.5', NP 173 pretty steady, VI 1.01, TSS 14.5

So riding at VI 1.05 cost me 63% more TSS than at VI 1.01, to go the exact same distance in virtually the same time.  I knew keeping the VI low was important, but until now I hadn't realized it made this much of a difference.

Chris G

 while that is true it is a strange way to illustrate it as 1.05 is a pretty darn good VI for a race of any length.  Check out the difference between 1.04 and 1.15 sometime.

And yes, riding steady is a wonderful thing.  It is the fastest way around on the power that you have.  period.

William Jenks

This is a really interesting comparison - nice to think of it.

The truth is that there is some mathematical distortion in intervals as short as 5 minutes because the software uses a data smoothing routine (30 s, if I recall). It's for that reason that it won't give statistics for intervals shorter than 5 min. This means you might be introducing a bit more unrepresentativeness than you mean.

What you might try to do is find a 20-30 minute interval with the same NP and widely varying VIs...not worrying about any other parameter. Not sure that there is any particlar reason why distance matters here.... TSS depends on "instantaneous NP" and time...not distance.

Cheers,
Wm

Bill McKinney

I put a longer post in the other thread you had up, but the reason the TSS is so much higher is that TSS is the SQUARE of your power (as % of FT) x time. I can't get exactly the TSS that you showed for the training ride, but the point is essentially the same. Here's how I think the math works:

Training ride: (223/233)^2 x (12.5/60) * 100 = 19.1 TSS
RR: (173/233)^2 x (15.5/60) * 100 = 14.2 TSS

I'm not sure where the discrepancy is (could be you had a few minutes > 100% FT), but your point is essentially the same, the TSS with the intervals in my math is still 33% higher. That's why you want to ride as steady as you can and avoid the power spikes...they impact your TSS exponentially.

Coach Patrick

This is also a great illustration of why interval work (or group riding) is a way better use of accumulating fatigue than just riding steady and long all the time (for the time-crunched athlete). Nice work with the Race Sims!

Coach Rich

...and another variable to add, that's not accounted for at all in WKO, is the impact of low vs high cadence cycling on IF and TSS. In other words, same TSS, same IF, same VI but one ride at ~85-95rpm vs another ride with long periods of low cadence cycling (climbing undergeared) can feel like very, very different rides.

When I train I basically try to make my rides <3hrs as hard as I can: crush the watts, crush the cadence, stand at 400w for no apparent reason, etc. I'm all over the place. I figure the more I can adapt my body to dealing with a wide range of conditions, I'll be better able to handle the long steady stuff and, more importantly, dealing with an funky stuff that a course throws at me. </p>