Power & Wind Resistance
Today I purhased Friel's new book: The Power Meter Handbook. I read through half of it today and found that it's (thankfully) not another cure for insomnia like its friend: Training & Racing with Power.
All is pretty straight forward and a good review of Power geek terminology simplified. But I do have a question for the Power Gurus in EN with regards to race execution for holding power.
Friel suggests (Page 82) that speed increases linearly and the power required to go faster increases exponentially due to aerodynamic drag from air resistance. Eg: going from 20-25 mph is only a 25% increase in speed, yet an approximate doubling of energy's required to go 5mph faster. He's saying this extra energy goes into sustaining that new speed, plus additional energy to overcome the headwind.
Long story short he's suggesting that maintaing goal watts during a downhill creates an "energy" expense for the additionlal mph above coast speed that will "cost you dearly!". He says this cost forces you to go deep into precious carb stores, while causing an Increase in H ions and therefore increasing blood acidity (this will happen when burning matches). He calls this execution "a wasted race".
Contrary to EN execution that says to hold goal watts on declines (which I do), Friel recommends to back off goal watts. He uses physiolgist, Alan Couzens, 50-40-30-20-10 Rule. At 30kph ride at goal watts (if this's your goal speed of 19mph). At 20kph (12mph) ride above goal watts (small hill). At 10kph(6mph) go well above goal power. This part sounds similar to EN philosophy for top AG athletes. But for 40 kph (25mph) Friel says to go below goal power (slight decline) and for 50kph (31mph) coast - get aero and stop pedaling (otherwise you execute "a wasted race").
Personally I aimed for 22mph for my last IM and would hold goal watts on dowhills and free speed still padaling hard up to 34-36mph, then coasting with speeds above this.
1. Would love to know what the schooled power peeps within EN have to say about Friel's suggestion?
2. How you execute your power/speed on dowhills and free speed zones?
3. How this affected with a tail wind?
Comments
From a simple energy conservation perspective, the closer you can sit to your AP, the better. The physical cost of higher power rises (about) with power raised to the power 4 — so, to minimise the cost of executing a bike leg, you need to minimise the departures from your AP. Of course, to do that you need to know in advance what your AP is going to be — but that is where the EN pacing guidlines come in.
Now this analysis assumes that you will only have small changes in your speed around your average speed. However, as we know that once you are around 50 kph (30 mph), the extra effort of trying to raise your power towards your target does not translate into a higher speed — which is why we coast around this speed.
As you suggest a tail wind should be dealt with as like a hill, but EN suggests that the wind may change (or drop) so it's better to just sit on your watts target.
I assume WSMs will also chime in.
Sukhi, let's take your IM FL as an object lesson. While you had no PM information, you did ride this flat course at what seemed to be a fairly constant speed and thus power level. Then, you had an awesome run afterwards. So you can ride for 5 hours at your planned IF of 0.73 (I bet you were 0.01 or 0.02 higher, in actuality), and still perform well overall. Why should hills or wind affect that? If FLorida had one hill in the middle, 1000' elevation gain at a mile 4% grade, could you not have maintained the same power output on the way up and the way down as you did on the flats? If so, as Peter says, why work harder on the way up, deleting precious energy, just so you can work easier on the way down.
The key thing is, there are two truisms:
This thinking may start to fall apart as the hills get shorter and steeper. At some point, even in the lowest gear, you will not be able to maintain cadence at your IF, and you will either have to decrease cadence or increase power. Steeper still, your cadence may get to be so low, you can't stay upright, so your choice is to get off and walk, or increase power. Similar thinking in reverse on the downhill: keep the same effort level until you spin out, then coast.
So I'd say Couzens'Friel make some sense on steeper (7% and above?), shorter (? less than 2 minutes) rises, but make no sense on downhills or with tail winds. Even then, "punching" up hills is a bad idea; going to 120% of FTP even for 1 minute will cost us dearly on the run. I've tried that strategy, and it doesn't work. But working @ 70% of your FTP on a downhill will not cost you a thing (remember, you rode a flat course at that IF the whole way, and had an awesome run), and will probably get you a bit faster overall.
@Peter, I'll take your 40 years of data analysis over my 8 months of power date analysis... : ) Thanks for your insights
There's one thing you said that I don't understand. You said, "the extra effort of trying to raise your power towards your target does not translate into a higher speed — which is why we coast around this speed"
Not sure if I'm reading this incorrectly, but when IF is .60 on a downhil and I start pedalling hard and bring it up to .70 it does translate into a higher a speed. So why coast when I could be going faster and still stay below my goal watts? This's my issue with what Friel's saying. He's saying that doing precisely this is executing a "wasted race" even though my VI will still be below 1.05.
@Brenda, Friel is speaking directly to us. He says "the longer the event is, like a 40km TT or IM" the more important this execution becomes.
@John, our body frames put us on opposite sides of the spectrum. I do power past people on the uphills (only letting my watts spike to a 20% max over NP goal watts), but I also bury them on the downhills too (riding a sliver below NP goal watts) It's on the downhills I'm now reconsidering my strategy???
@Al, Thanks for your piece. You're essentially saying to continue to execute the way I have been. I never let my IF go above .95, I'm pretty controlled on uphills. My issue on the downhills may be that I used to street race motorcycles and I LOVE going fast. So climbing up to 44-45mph on a downhill is not uncommon for me and puts a pretty huge smile on my face... : )
I'm racing IMCanada for 2013 and although I live a short 75 minute drive from Whistler, the IM bike course is presently covered with snow so I haven't drove it yet to expereince the grades and elevations. As you know its an unknown course, IM claims that it's similar to Penticton and IMLP.
Here's the bike elevation: http://www.ironman.com/~/media/6ba06fa8d4b249f08b81211e93bc917e/imwlrbikeprofile1logo.pdf
I like to train on similar terrain as the course itself (this year RR's will be on the actual course), that's why Friel's suggestion of backing off goal watts on downhills jumped on me. So you're saying your experience does not support Friels theory. Holding IF of .73-.75 should be held on the donwhills too. This's what I was planning to attempt to do. Backing off these watts would produce a much slower bike split as you can see from the course profile there's a significant amount of downhill...
I think there is something to it, but it depends on the race distance. I guess the point Friel is making is that if you coast down a certain hill, you make forward progress at a certain speed for free, whereas if you maintain power, you are using energy for not much speed gain.
Let's imagine we find a race with a hill, and it has a 5 mile minor descent.
Scenario 1: I coast the entire time, and go at 22mph. That means I'll make forward progress for 5 miles, or 13.6 minutes, and consume zero energy to push my bike forward.
Scnario 2: I try to maintain my target power of, say 200 watts and this power makes me go down the hill at 25mph, which means I'm now pushing 200 watts for 12 minutes. Quick calculation shows this is 144 kJ. If this were an IM and my FTP were 275 watts (200 watts would be racing at IF 0.73) then the cost of pushing the bike would be 10.7 TSS.
Long story short --> if I'm holding power I save 1.6 minutes over that descent versus just coasting, at a cost of 10.7 TSS. If there would be 5 of these hills along the course then obviously TSS would add quickly, the time savings would add up also but the consequence of this high TSS difference could become a major factor during the run.
Personally, with my own limited experience, I'd look at downhills as an opportunity to conserve energy, eat & drink, do an assessment how I'm feeling, what I need, spin the legs out, etc and definitely don't push at target power.
Short course it is totally different, because every second matters and if you are a powerful rider you don't just make a difference on the flats but also on the downhill.
Ben ... The goal here, of course, is for Sukhi to go,as fast as he possibly can on the bike/run in an IM. Key word, of course, is "possibly". So, for his best possible time, he needs to do two things on the bike' as far as power management is concerned:
There is no advantage to him to "save" TSS points. He has already demonstrated he can run welloff of a hard bike, confirmed in his RR. So he wants to use up all of those TTTpoints without going too much over or under at any moment his power target of 73/4% of his FTP. Coasting down hill, as you note, loses him time.
And he also wants to maintain as even a pace as possible while going uphill. Someone who knew a bit about pacng, racing, and winning IMs, Paula Newby Fraser, who competed without a power meter for most of her career, said (or at least her coach did), "you can lose three minutes on the run for evey one minute you go anaerobic on the bike."
It's not possible to tell from that profile much about the meter by meter gradient on the climbs. If it's truly like Penticton, there are no really steep grades, and it should be possible to get a 1.02/3 VI there. Going too hard up a climb, and too easy down, will both *raise* the VI, and cause you to,either leave energy (up) or time (down) out on the course, both affecting your final time.
If you read my RR from IMNYC, you'll recall that I pedaled at goal watts halfway down every small hill (and there were many) and then coasted. I passed a ton of people on every hill. Plenty of the people I passed near the bottom were pedaling the whole way down and I passed them while I was coasting because I was pedaling harder (but at goal watts) near the top so I got to my spin out speed faster then them, and then I got super low and coasted past them as they stayed high in the wind and made turbulance with their wide legs as I had my knees together and my chest practically on my seat. I didn't read it yet, but I think this must be what Friel is addressing. At some point, you can actually go faster by coasting and being more aero, and at no energy cost to your legs.
There's one thing you said that I don't understand. You said, "the extra effort of trying to raise your power towards your target does not translate into a higher speed — which is why we coast around this speed"
Not sure if I'm reading this incorrectly, but when IF is .60 on a downhil and I start pedalling hard and bring it up to .70 it does translate into a higher a speed. So why coast when I could be going faster and still stay below my goal watts? This's my issue with what Friel's saying. He's saying that doing precisely this is executing a "wasted race" even though my VI will still be below 1.05.
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@Sukhi — sorry I wasn't clearer
The point I was trying to make was that if you are doing (say) 32 mph downhill, then if you sit on your goal watts that hardly gives you anymore extra speed compared to just coasting — which is why we coast above these speeds and save energy.
Also, I wouldn't ever deliberately go more than 10% above my goal watts (and then only as WSM Al points out for a short hill). The cost of your 20% suggestion is very big IMO.
Personally I aimed for 22mph for my last IM and would hold goal watts on dowhills and free speed still padaling hard up to 34-36mph, then coasting with speeds above this.
I agree with this. When at the Madison tri rally last year Rich liked to use the phrase "conservation of momentum". This was not a nicer way to say "pedal your ass off on the downhills". Rather, it was about being very strategic about the downhills and flats. What was NOT recommended was to crest the hill, hit 27-28 mph and start coasting. Rather, keep your power up over the crest and the first part of the downhill until you hit the mid 30's mph, THEN coast (and pass all the suckers who didn't keep up their power as the crest turned into a downhill). When you start to flatten at the end of the downhill, keep that power up, thereby conserving the momentum from your downhill. I do not think the EN execution methodology is not about pedaling until you spin out all the time. Overall using the EN execution approach clearly you will do less coasting than most others. But there is certainly a speed above which the optimal decision is to coast.
There are some threads that advise of the "optimal" speed at which to coast based on a set of variables that are person-specific (weight I think being the most important). Personally I wait until a pretty high speed to coast. Your 34-36 sounds about where I'd typically coast.
My own goal is to hold watts going up hill or down a hill with the same steady RPE/watts . I personally don't go as hard as EN suggests on a downhill, say IMLP which is a down mountain, forget about it I'm covering the break at that point. A hill, rolling type hill with a slight grade, sure I can do makes sense and isn't that difficult to do.
A tail wind to me is free speed I hold my watts and enjoy the sail effect.