Power Meters – For and Against

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Garmin Vector Pedal Power System

Power meters in duathlons and triathlons are not new. What is new is the rapidly falling prices, the numerous technologies and the increasing take-up.

A power meter seems to be the holy grail of a good bike split. Is it?

I use a power meter. I use one a lot for training and often for racing. I use it in conjunction with heart rate and ‘feel’. I find it particularly useful over shorter distances…but that’s just me. I go out for rides for fun and sometimes NEVER look at the wattage.

I read an article at training peaks this week about 8 great things in favour of power meters (the headings below). I mostly agree with what was said but there are some counter arguments to be made and I’ve made a brief, first stab at those counter arguments, below.

1. More Accurate Training Measurement

At any one instant heart rate, or indeed how you ‘feel’, does not necessarily correspond to the effort you are exerting.

A: Yes a power meter is pretty much instant compared to HR

Furthermore other factors like caffeine/hydration affect HR

A: Well yes that’s true. But some of those other factors also affect the levels of power you can maintain as well. 300w when dehydrated has more of a stress on your body when properly hydrated – as to whether the physiological adaptation to the 300w is the same in those two instances I confess to not knowing. I would have thought the adaptation WOULD be different.

2. Quantify Your Training Load

Power can enable a better view of day-on-day intensities and volumes.

A: Well yes it can. That’s great for cyclists. But how do you do it for running (stryd, maybe) and swimming to work out your true training load?

3. Training Specificity

Specific levels of effort can be specified for training for your exact event.

A: Yes.

4. Improve Training Efficiency and Quality

Eliminate junk miles

A: Yes. You can do that easily enough with HR zones as well.

5. Quantify Improvement Over Time

FTP can quantify improvement over time.

A: Yes. On a turbo trainer this is pretty definitive if you can motivate yourself sufficiently and prepare uniformly for such tests.

You can do a similar sort of thing with your swim time over a certain distance or with a local 5k or with  your local bike-course-PB time. With running external factors could more readily come into play. You could test your rising LTHR over time or your lowering HRmin over time but I would accept that for cyclist FTP improvement (in terms of w/kg) is great.

6. Best Identify Strengths and Weaknesses

Power profiles can be used to identify strengths/weaknesses.

A: Yes, very much so.

7. Race Day Planning and Prediction

Planning and executing a precise race strategy is fairly easy with a power meter.

A: It is but relying on targeting a precise wattage at an given second is very difficult in real world conditions away from your turbo trainer. I find the 30 second moving average is most useful. Then again it takes your HR about 30 seconds to respond so you can use that too 🙂

8. Use of the Latest Scientific Models

There are lots of power related tools that you can use if you are very serious about your cycling.

Other Negatives

A good power meter will currently cost you over £500, probably quite a bit more. All this is changing though and within a year ie end of 2016 I would expect a highly price competitive market from the market incumbents and the many new entrants starting to sell their products now.

A single power meter might not work on all your different bikes as well as on your turbo trainer. It might not be portable to your MTB. If you get more than one power meter from different vendors or even if one power meter is older than the other identical one then you might get a 5% difference. Will all those external factors mentioned earlier affect your HR by more than 5%??

What if your power meter breaks? If your HR strap breaks, then a replacement is as cheap as chips (if you like lots of chips).

Some power meter solutions seem to dislike carbon cranks.

Power meters usually require (simple) calibration before usage.

Your training FTP at sea level won’t readily translate to a race FTP up the Alpe d’Huez. HR zones are also obviously affected by altitude.

I’m not convinced by the argument that ‘power is power’. a 95% of FTP session for 2×20 minutes is surely NOT the same if you do it day after day after day. In this extreme example, fatigue levels accumulate day after day and at some point you would be unable to do the session. So fatigue states affect the physiological cost of using certain power levels and yes, of course, when preparing a training plan a coach would take that into account.

As I say, I’ve got a power meter (or two 😉 ). I’ve also got a HR monitor (or ten)

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