Power Meters and Pedaling Effectiveness

RapDaddyo

I recently resumed serious cycling after a 30-year absence. I’ve been riding for about 2 months at about 14 hours/week. After a few more months, I plan to start road racing again. Hopefully, the boys have slowed down a touch in my age group. Apart from some improvements in bikes and components, the biggest change in equipment and data seems to be the introduction of power meters. I plan to buy one and use it in my training program. I have read everything I can find (including this forum) about the various models currently available and how to use them correctly. But, I still have a few questions.

First, there is lots of data and discussion about the accuracy of power meters under different circumstances, as well as installation issues, durability and the like. What I can’t find is much discussion of using power meters to develop and test pedaling effectiveness, optimal cadence, crank lengths and riding positions. Do all power meters (SRM, PT, Polar, Ergomo) capture and download data on symmetric/asymmetric pedaling patterns? Is there a difference between the devices in this area? Can these data be analyzed post-ride at different combinations of power/cadence? It would be nice to be able to put a marker or “flag” at certain points during a ride such as the beginning of a test. This would help with post-ride analysis. Do any of the models support this? I read that the PT has an interval feature. Is this a before/after flag on the data timeline?

Second, it is clear that the Polar doesn’t work well on a trainer, I assume because the chain tension is not representative of actual road resistance. It appears that the PT works fine with trainers. Do the SRM and Ergomo models provide realistic and accurate data when used on a trainer – say, Computrainer?

Woofer

The SRM has a special torque analysis model that requires the user buy the Pro SRM + the 700(?) dollar special modded PC IV computer that allows instantaneous torque analysis on your PC. (Current SRM's comes with a PC V computer and the PC IV is out of production except for this option) This can only be done on a trainer since one output from the CPU goes to a computer. Whether or not this is of any value is up to you.

All of the conventional power meters work fine and have their own quirks. Quit comparing the Polar guestimator to them. You never know if your Polar is actually working unless a.) you have another powermeter attached to your bike b.) you are doing a steady state climb and can verify the data versus analyticcycling.com.

re:intervals - I never do ride analysis on the CPU while on the ride. It's much easier to download the data and do whatever you want with it later. I have a SRM and a PowerTap and used to have a Polar, and I don't even care if they have an interval mode.

RapDaddyo

Thanks for your reply, Woofer.

The marker or flag feature I am talking about is something to use in post-ride analysis. For example, I want to do some steady grade climbs at the same power but at three different cadences and compare my HR after, say, 5 minutes of steady-state effort. I would want to mark the start and end of each test so that I could quickly go straight to them on the data timeline on my computer after the ride. I could try to remember the elapsed time of each segment, but that seems a waste of mental energy, and I don't know if I even could remember 5-6 of them on one ride. I don't know if any of the power meters support have such a capability.

ric_stern/RST

The SRM and PT both have interval markers. If memory serves me correctly so does the Polar. The Ergomo does *not* have any interval markers -- these have to be done post ride in the analysis software.

Almost certainly your HR will be lowest at a given power output at a lower rather than higher cadence. This is because lower cadences are more efficient. The most efficient cadence will increase as power increases. However, it is likely that more moderate (i.e., approaching 'normal') or a 'normal' cadence will be less fatiguing than the most efficient cadence. Additionally, you are probably best just self-selecting a cadence that feels 'good' and allows you to generate the most power for the task that you are doing (irrespective of HR).

The Ergomo just doubles the power that you generate with your left leg as your total power output. The SRM and PT displays the total power that you produce.

The SRM and PT will agree closely with each other (there should be a small difference of around 2%/ ~10 W) with the SRM reading higher than the PT (due to drive train losses). They may or may not agree with a Computrainer, but work fine on it or any other trainer.

Ric

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http://www.cyclecoach.com

Woofer

If you get the SRM, it is *very* easy to note intervals off in the included software down to the second ( or whatever you set the recording interval). It has simple tools to edit the start and stop time offline and your actual periods of intervals are easily found by visual examination of the power data. The PowerTap software can do this but it is a pain to do this, but it's possible. For me, it's not so important that I have marked in the intervals this stuff, but that I do each interval at the prescribed effort level and time. I got tired of fiddling with the buttons on the bike. I just notate the workouts right after I download them. I never work very hard unless I am doing an interval or effort so it's easy for me to visually inspect the data and pick the items out but that just may be me. One doesn't have to remember hardly anything except what workout one wants to do on the bike and do it.

One aspect of using a powermeter is that to get the most out of it one should download the data, and after you start downloading every ride, you realize you get the most out of it after the ride.

RapDaddyo

Great input! Thanks, guys. By the way, if you ever get to LV and want to do some loops, rolls, split-Ss and pull about 5Gs, let me know. That'll get your HR up.

Woofer

One more thing, if cost is no object, you can get a version of the SRM with adjustable length crank arms. The value of this and the torque analysis is debatable but I'm not an expert. I think you would get more out of a coach who's worked with someone like you and power meters.

RapDaddyo

Thanks. That's good to know, because I was thinking about going to Mammoth Lakes (about a 5.5 hour drive for me) for a session with Tom Slocum at High Sierra Cycle Center. One of the things I would learn is what length crank arms I should be using and if they are equal. I've never done a dynamic pedaling analysis session, so I don't know how symmetrical my pedaling action is. Depending on what I find out, I may have a lot or (hopefully) a little work to do to get more symmetrical and efficient. And, one of the contributing factors may be that I need different length crank arms. So, it may be very valuable or not valuable to be able to have adjustable length crank arms. I'll do that session before I invest in a power meter. Do you know Tom Slocum?

RapDaddyo

I'm having a problem finding descriptive information on the SRM system(s) in English. I can't find an English version web site and the German website has only a few non-technical articles and the Technical Manual in English. Do you know where I could get more info. about the SRM product(s) in English?

RapDaddyo

Thanks, Ric. You're right about the relationship between cadence and efficiency. While I don't have a power meter yet, I designed a test that should have resulted in equal power. I have a nice long, relatively constant grade hill here. I did four 5-minute climbs (with 10 min. easy pedaling after each) in four consecutive gears, with cadences computed to maintain the same speed. The cadences were 113, 100, 91 and 84. My HRs were 150, 148, 145 and 143 respectively at the end of each 5 minute climb. Interestingly, the cadence that 'felt' the best was 91, even though I am most comfortable at about 100 on the flat. So, the feel and the HR were at odds with each other. Now, I would assume that HR is a predictor of fatigue and that I would have more endurance at the 84 cadence, even though I felt better at 91. Is HR a predictor of fatigue?

Woofer

One thing about varying cadence, you may have some sort of adaption period.

re:crank length - get fitted first. Try riding in the fitted position for a while and see how it feels.

Their old translated stuff describes what they have.

http://www.srm.de/old/torque.html

http://www.srm.de/old/mulcrank.html

http://www.thebikeage.com/srm_faq.htm

I don't know about Slocum, I live in Northern CA. I have heard good things about Christopher Kautz(sp) and UC Davis up here. Doesn't Kraig Willett live down in SoCal?

ric_stern/RST

why do you think that you may need different crank lengths. I've only seen this in one person, who had a functional disability and had one leg significantly longer than the other.

As regards crank lengths themselves, i would just choose the ones that feel the most comfortable or are the same on all your bikes. Research by Martin et al. showed that there was no significant difference on performance with a variety of different crank lengths (and therefore cranks should be chosen on e.g., comfort).

Ric

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http://www.cyclecoach.com

ric_stern/RST

to do a good test, you would need to randomise the order for all the trials, and repeat the test with each trial in a different order... obviously, this couldn't be done in a day so other variables would affect things...

HR isn't a predictor of fatigue and is only a predictor of how fast the heart is working. This is a 'proxy' for the effort that you're doing. The only thing that really matters is whether you can produce the desired power for the desired duration.

ric

__________________
http://www.cyclecoach.com

RapDaddyo

Thanks, Ric. Actually, I don't start off assuming that I need different crank lengths, or that I have an assymetric pedaling form, or that my pedaling stroke is inefficient. What I start off assuming is that I don't have any data except how I feel. At this point, before I spend a few hundred hours riding and trying to improve, I thought I'd like to get some objective data. I know a lot about the golf swing, and I know that what we 'feel' we are doing is often not what we are doing. So, I know that even though I may feel that I have an efficient, symmetrical stroke that I may in fact have a very inefficient stroke. I just want to deal with facts and not just feelings only.

By the way, I can't find an email address or web page for Kraig Willett. I think he is in the San Diego area. Do you know how to reach him?