I am now about seven weeks away from my A race this year, the Utah Half-Tri. My training is going pretty good, and I constantly think about what my final bike goal should be. I normally determine this based on my current training speeds and times (mostly the 56-milers that are close to what the race will give me).
Now I find GG and his R.A.N.T.’s over at GGTri blog/website. I don’t even know how I ended up on his website just a few days ago, but I read it and I liked it. He got me thinking about how much a half-mile-per-hour increase costs in terms of Training Stress. I hadn’t really thought about that. I have always just been looking to INTUITIVELY KNOW a pace/effort I can hold and then run fairly decent afterwards. But this TSS thing got me thinking.
For most triathlons, you spend the most time on your bike. If you want to be a faster triathlete, it makes sense to be faster on the bike. So if you are doing long course races (70.3 to 140.6), this means that you can cut substantial time off your total race by maximizing your bike speed… right?
The short answer is yes & no. Yes, you can have a good bike split, but it may result in a really poor run… more than negating the gains you made by riding fast. Here’s why: The physiological cost of increasing your speed is not linear. In the following example for a full IM, a 5% increase in bike speed will “cost” you more than 21% in additional total physiological stress on your body.
Let’s play with some numbers:
- If I average 18 mph on the bike for 112 miles, my total ride time would be 112 miles / 18 mph = 6.22 hours (6:13).
- If I can squeeze out 5% more speed, my average speed would be 1.05 x 18 = 18.9 mph. Getting an additional 0.9 mph can’t be too hard, can it? At 18.9 mph, my total ride time would be 112 miles / 18.9 mph = 5.93 hours (5:56). Basically 5% more speed translates to a 5% time savings, or nearly 17 minutes on a 112 mile ride. That is a big savings.
Those are deep thoughts. But how do you quantify that? He explains….
- At 18 mph (see note 1 below for model / input), the required watts on a flat road is 116.51.
- At 18.9 mph (same input conditions), the required watts on a flat road is 131.93.
- The increase in power required is 131.93/116.51 – 1 = 13.23%. So to go 5% faster… you need to produce 13.23% more power (physical work)
But wait, there’s more. Now he talks about TSS, Training Stress Score. I always thought that was a way to look at training, but you can also use it for race planning. I have definitely learned something today. He says…
So, if you could produce 185 watts for 1 hour at maximum capacity, your IF for a ride at 116.51 watts would be: 116.51/185 =0.63. At 131.93 watts (second scenario), your IF would be: 131.93/185 = 0.71. Using these to calculate Total Stress Scores:
- TSS for 18 mph = IF x IF x Duration x 100 = 0.63 x 0.63 x 6.22 hrs x 100 = 246.9
- TSS for 18.9 mph = 0.71 x 0.71 x 5.93 hrs x 100 = 298.9
- The resulting increase in physiological stress: 298.9 / 246.9 – 1 = 21.1% increase.
So the question is: Is the 5% bike speed increase is worth the 21.1% increase stress on your body? As a rule of thumb, the upper limit of TSS scores during an IM is around 280 for a strong IM athlete and an upper limit of 260 for weaker runner or novice IM athletes. Few pro’s push to 299 TSS values, so likely the 5% increase above would likely result in a poor IM run overall
That’s a lot to digest in a bit, especially for a guy like me who doesn’t like math but DOES like to know answers to that type of question. So what to do? Well, I am good at replacing my numbers in somebody else’s equations, so let’s take a look at my own specific needs here in relation to his specific thoughts.
I want to increase my race pace from 18.5 (St George 70.3) to 19.7 (Utah Half), which is . Let’s start at the top and kind of copy my info into his math from the calculator at www.gribble.com (I used all defaults except biker and bike weight).
- If I average 18.5 mph during a 56 mile bike, that is 3.027 hours, or 3:02, exactly my time at St George.
- If I average 19.7 mph during a 56 mile bike, that is 2.842 hours, or 2:50:30, pretty much my goal at the Utah Half.
- If I go 2:50 instead of 3:02, that is 12 minutes faster, or 6.6% faster (12 minutes / 182 minutes). I don’t know if that math is right, though because there isn’t an example of that formula. Aaargghh… Mrs Fenster back in 6th grade…help please!
- At 18.5 mph the required watts is 153.88
- At 19.7 mph the required watts is 180.2
- The increase in power required is 180.2/153.88 – 1 = 17.1%. So to go 6.6% faster… you need to produce 17.1% more power (physical work)
Now for the look at TSS. My FTP as set on TrainerRoad is 240, using a Kurt Kinetic power curve but not a direct power meter. That number is good enough for me on this calculations. Let’s put my numbers into his example below and see what happens.
So, if I can produce 240 watts for 1 hour at maximum capacity, my IF for a ride at 153.88 watts is: 153.88/240 =0.641. At 180.2 watts (second scenario), my IF would be: 180.2/240 = 0.75. Using these to calculate Total Stress Scores:
TSS for 18.5 mph = IF x IF x Duration x 100 = 0.641 x 0.641 x 3.02 hrs x 100 = 124.09
TSS for 19.7 mph = 0.75 x 0.75 x 2.84 hrs x 100 = 159.75
The resulting increase in physiological stress: 159.75 / 124.09 – 1 = 28% increase.
Wow, that was strangely fun! And incredibly insightful. I am trying to increase my TSS by 28% for this race. That would be significant if there weren’t a few major variables at play, such as the lack of a major hill in the Utah race, additional really good training in June and July, and the mostly flat course. And that doesn’t figure in the “enemy” of the day being heat and wind. But it is very insightful, and would be very useful if I had a direct power meter on my bike (alas, I am living the dream with a wife, kids, dog, and mortgage, so…).
Now let’s apply all that knowledge to gather up some wisdom. GG writes….
As a rule of thumb, the upper limit of TSS scores during an IM is around 280 for a strong IM athlete and an upper limit of 260 for weaker runner or novice IM athletes. Few pro’s push to 299 TSS values, so likely the 5% increase above would likely result in a poor IM run overall (see note 3 below for more information).
That was something else I learned. I searched for the standard age-grouper goal for TSS during a 70.3 and found “the generally recommended range of .75 to .85 for age groupers racing the 70.3 distance” on a Training Peaks blog. That works for me, and I think I’ve seen/heard that before.
So, in summary, my increase from 18.5 mph to 19.7 mph is 12 minutes faster, requires 17% more power, and a 28% increase in TSS (which at 19.7 mph is at .75 on the low end of the generally recommended rage of .75 to .85 for 70.3 distance age-groupers.
I think the math required above is all pretty much spot-on, using my very subjective method of looking at previous races and training. Just this morning, I rode 19.7mph at a very easy pace for 24 miles, and I’m pretty sure I could hit that pace for another two hours and be able to run fairly strong. In fact, I followed that 19.7mph effort on the bike with 6.5 miles at a 8:20/miles, thinking I want to run 8:40/mile during the race.
What if I did an intensity factor of .80? An FTP of 240 watts x.8 = 192 watts. Using the www.gribble.org calculator, that gives me 20.20 mph which is a time of 2.77 hours or 2:46:12. Is that 0.5 mph and 0.05 intensity factor worth 4 minutes? I don’t think so, especially given the fact that I am expecting it to be really hot and will therefore want to be careful about bonking.
So, I guess I’m going with a goal of 2:50:00 for my Utah bike leg!