Intro to training with power

by Dan Empfield 4.8.02 (www.slowtwitch.com)

The subject at had is the use of power as an arbiter of effort while training on the bicycle. This will be the first of what I intend will be many articles on this subject. This is only an overview, and the fact that it wiill contain themes you’ve not read before is a testament to how little has been written on this subject by people who’ve actually used power as an informational parameter.

The first time I ever rode a significant effort with a power meter was on a climb up Mt. Palomar, in which a rider ascends over 4000’ in just under 12 miles. I rode it in a way I considered conservative, and it was conservative compared to other of my efforts up this hill. I was trying to achieve a balanced effort. When I started I was producing a steady 320 watts, and I felt fine. Truth be told, I felt pretty good all the way up. Yet mile after mile I saw my power output drop, to 300 watts, then to 280 watts, and to the point where, when I was nearing the summmit, the only way I could produce 240 watts was to get out of the saddle. It was a startling example to myself of how deceived I’d been in every previous attempt up this ascent.

Yes, I could’ve discovered the error of my ways with a heart rate monitor, but not with the clarity that a power readout afforded me. Indeed, I rode with a fairly steady pulse. It was probably just 5 - 10 beats too high the whole time. Climbing a large hill on a bike is probably the most obvious indicator of the differences between using pulse alone versus power plus pulse, or power only. I can ride that mountain with my pulse at 170bpm the whole way. One might suspect that I’d go faster at a steady 170bpm than if I’d ridden it with a pulse of 163 for the first two-thirds, and 170 for the balance. If I’d ridden the hill with a more conservative heart rate, though, I’d probably have started the ride at 290 watts and ended at 270, with an average output of of 280 watts instead of an average of 260 or 270.

After riding with a power meter for awhile one starts to gain a new appreciation for the mistakes that can doom a triathlete’s race. One of the two ways a triathlete can clobber him or herself during the cycling leg is to end up with a power output that is considerably less than the average for the entire ride. As my ride up Palomar demonstrates, if I’ve done the ride at an average of 270 watts but I’m cresting the summit at 220 watts, that’s an indicator of what kind of power I’ve got (or more precisely the power I haven't got) while entering the run. If I’m finishing up at 260 or 270 watts I know I’m a lot less likely to fold in the run, where big time can be lost.

The second mistake concerns one’s peak power during a ride. It’s remarkable to me how I’ll attempt to ride a balanced effort
averaging 240 watts and never exceeeding 350 wattsand find out after I’m done that I’ve put out 500 watts somewhere during the ride. It’s easy to do this and to not feel the effort, because cycling has a rest component (during descents and corners) that running and swimmming do not contain. It’s the hill that’s a bit too steep after a bit of a rest that’ll do me in. No, I won’t feel the negative effect of this effort while I’m doing it, but I’m bound to feel it later, if not during the ride then during the run. In this one narrow instance a heart rate monitor isn’t going to pick up this mistake, or if it does, it’ll only chronicle the mistake you’ve already made.

This is why power is a useful tool for the triathlete, probably even more so than to the bike racer. A mass-start racer doesn’t have a lot of choice in the matter. When the group goes, you go to. You can’t afford to say, “Let the fools go. I’ll wheel past them later in the ride by virtue of my better techniques of energy conservation.” But triathletes can afford to take the long view. Indeed they must take it, not only for the sake of the rest of the ride, but for the sake of the run as well.

I’m convinced that the bane of the triathlete during the bike segment is the peak power one puts out, and not only in terms of too many watts now and then during the ride, but peak power inside the pedal stroke as well. The problem is the inability to easily recover from a particularly ballistic muscle contraction. Putting out 500 or 600 watts
when the ride is going to be performed at an average of 220 or 230 wattsmeans some significant and perhaps unwarranted work has been done. Imagine that I asked you to bench press one ton in total. Imagine that what matters is getting these two thousand pounds pressed as quickly as possible, yet you could do it any way you wanted: 10 times 200 pounds, or 20 times 100 pounds, 50 times 40 pounds, or 100 times 20 pounds. Then imagine that after you’re finished you must immediately perform 50 push-ups.

There is no right answer for everybody. Stronger athletes would choose to press 200 pounds, others might choose 80 pounds, or 40. The problem occurs when an athlete tries to press 200 pounds when his max is 220. What sort of ability will he have to keep going after he’s pressed 200 pounds twice or three times? He’s still got three-fourths of the weight yet to lift, and even then he’s got the push-ups to look forward to. There comes a point where he’s “shot his wad” and there's no easy way back from that. While a slow twitch athlete might be able to recover from running or swimming slightly too fast for slightly too long, it’s hard for a slow twitch athlete’s muscles to recover from a ballistic fast twitch effort.

I’m convinced this dynamic is what happens to too many triathletes, and the insidious nature of this is that the problem is not manifested until much later in the event. It’s like punishing your dog three days after he’s chewed your shoe. He knows he’s done something wrong, but he can’t remember what or when.

It’s not simply a case, however, of these higher-than-optimal work levels occuring now and again during the ride. When one’s cadence is too low, they occur every pedal stroke. This is another area during which a power meter speaks volumes. It used to be that I took glory in the ability to climb a hill with a larger gear than I’d used in times past. Yes, this might be indicative of an ability to generate more peak power, and this would be a good achievement for a mass-start cyclist. But in terms of simply getting up the hill faster a power meter tells a different story. It’s uncanny how often I shift into a lower gear and my power reading actually goes up. There are equipment anomolies that can explain this which I’ll describe in further articles, but what I’m talking about is power that increases and stays higher when I gear down and ride a higher cadence.

For me, riding at a higher cadence means that I’m bench-pressing 80 pounds more rapidly instead of benching 100 pounds less rapidly. God seems to have made my muscles in such a way that they can recover quickly from less ballistic exertions, and when the peak power during the pedal stroke is too high, bad things happen to me over time. I find that my ability to ride with an optimal power output for the longest period of time, and feel the least worn out at the end of it, occurs at a cadence of 90+ beats per minute. Surprise, surprise. This is precisely what one sees when watching the world’s best time trialers perform during the grand tours.

Yesterday I rode a time trial. It wasn’t a race. It was on my own “private” course which takes me through 32 miles of variable terrain including perhaps 1500 to 2000 total verticle feet. My goal in these efforts is to achieve the best time while conserving as much effort as possible for a hypothetical run afterward (which I rarely do, but the thought is there). I’m not in particularly good cycling shape right now, but I rode a surprisingly strong time considering how disappointingly I rode the hills. I also finished the ride relatively fresh. The difference? This is the first time I’ve ridden this effort using a power meter (In my case it was a Power-tap system).

I was disappointed in the way I rode the hills in my time trial because I did not ride them as quickly as I’d ridden them in times past. Yet when I tried to ride more quickly my power output was way too high—too high for me to maintain for very long. It is obvious to me that I’ve not been applying my power wisely. I’d been riding the hills like I was in the middle of a mass-start race, not the way a time trialer should.

I’m preparing for the Wildflower Long Course Triathlon, and last year I rode the bike course with an 11-23 cassette. This year I intend to ride the course in a faster time, yet I’ll be mounting a 12-27 and I suspect I’ll be using the 27-tooth cog. Having a power meter on the bike has “validated” my use of the smaller gears. I don’t have to be self-conscious or disappointed by resorting to the use of a gear that I know I don’t “need.” The power meter is the absolute arbiter. If it says it’s best to spin the 27-tooth then that’s what I’ll do.

There are a variety of other interesting things you discover while training with power. One is that you can’t ride a variable-terrain course with an even application of power. At least I don’t seem to be able to do it. I can sustain 280 or 300 watts while riding up a hill for a pretty long time. But putting out 300 watts on the flats is a tough go for very long. I don’t know why, and I don’t know if this is universal. One of my riding partners, Pete Pennsyres, experiences the same phenomenon, but an athlete he coaches that can output more power on the flats than on the hills, all other things equal. But I think this is rare.

I do not believe that power is a replacement for HR-based training. Regardless of what your power meter says, if you know that you can perform an Ironman-distance bicycle ride at 150 beats per minute—and that going past that is a recipe for trouble—this is a truth to which the power meter must defer. Yes, of course you can make that same sort of determination using your power meter, i.e., you’ll learn that you can ride 112 miles while keeping to 190 watts on the flats and 240 watts on the steeper hills. But what if your race takes place on a day that is hotter or more humid than is usual for you? Riding at your "normal" power output might kick your heart rate up 10 beats a minute, and throw you out of your zone.

Let’s say you want to train with a power meter. Which one should you get? There are three well-known options at the time of this writing: SRM, Power-tap, and Polar’s power adapter that interfaces with its S710. We’ll put these alongside each other in a future article. The Power-tap and the Polar unit are more easily accessible in the U.S., as they are both sold through a wide variety of retail locations. Each is going to set you back more than $600 or $700. Each has advantages. The Power-tap is more precise. Polar’s boast is that it doesn’t replace a piece of componentry (the SRM replaces your bike’s crank, the Power-tap repaces your bike’s rear hub). Both SRM and Power-tap work using strain gauges, and the Polar unit works by measuring, among other things, your chain’s vibration (the harder you pedal, the more tension you put on your chain, and it’s vibration frequency is a measure of that power).

Both the Power-tap and the Polar power unit function as full bike computers, including HR monitors that read out on the computers’ handlebar mounted screens.