As I discussed in the first installment of this series, the price of equipment for triathlon is high and often the return on investment is measured in seconds, if that, over the course of a race. Invariably though, the pull of new gear is inexorable and once people start in the sport it is only a matter of time before they find themselves wanting what they see their friends and competitors have.
My general advice is, as I said in the last article, to resist this pull for as long as possible. Investing in yourself is generally always the smarter and more fiscally responsible play when it comes to improving in this sport. There is however one investment that I will always encourage and that is because of all the things that you can spend money on, it will not necessarily make you any faster but it can definitely make you a whole lot smarter about how you train and race.
That investment is a power meter.
When I first started in triathlon over two decades ago, the only power meter on the market was the SRM. SRM is a German company that developed the technology for bicycle power meters and first brought it to the professional cycling ranks. Eventually it made its way to age groupers but with an incredibly steep price in the thousands of dollars. SRM is still around and is considered by many to be the gold standard in power meters but buying one can often feel like you are paying for gold because their prices haven’t really changed that much from when I first learned about them.
Fortunately, many other companies have entered in to the market and with that kind of competition the prices for power meters have gotten to the point where they are extremely affordable. I now tell all of my athletes that if they have any notion of being remotely serious about cycling, spending the $500 or so for a power meter is a very smart decision that will pay off handsomely for years to come.
So what are power meters and how do they work? Why do I and almost all other coaches believe they are so vital to informing bike training and racing and what are the options for finding one that works for your specific need and budget?
What are power meters and how do they work?
Like speed and cadence, power is simply another metric that can be measured during the bike portion of a triathlon. While speed is measured in miles or km per hour and cadence in revolutions of the crank per minute, power is measured in watts and relates to the amount of force being generated by the rider to move the bicycle forward.
Power, speed and cadence are all inter related but power is very much the independent variable. That is to say, speed can be influenced by the terrain you are riding on, the weight of the bike and the rider and wind resistance. Cadence can be influenced by what gear you are riding in but power is entirely dependent on how much force the rider is applying to the pedals and directly impacts speed and cadence. So measuring power is a much more reliable means of determining the effort of the cyclist than anything else.
Power meters are devices that contain strain gauges and measure force in newtons. The meter then transmits this information along with the amount of displacement of the meter (more on this in a second) to the head unit so that a conversion can be made in to watts. 1 Watt is equal to 1 Newton-meter/second. So if you apply a force of 1 Newton to displace the power meter by 1 meter in 1 second that will give a reading of 1 Watt. The math is not so important but understanding the idea that power meters measure force and displacement is.
Power meters for bicycles can be located in four different places each with their own pros and cons (I’ll discuss those later). Meters can be in the pedals, the crank arms, the chain rings or in the rear hub of the wheel. Because the power meter measure both force and displacement, power meters located in the pedals and crank arms have to be calibrated with the correct crank arm length otherwise the conversion to watts will be incorrect.
How are power meters useful for training and racing?
Because power is a measure of rider effort, it is a much better measure of training load than anything else. As a coach, I can prescribe workouts based on your individualized power numbers to build strength, endurance or ensure recovery. As an athlete, you can use your power meter to ensure that you are doing the work needed to get the kind of results from your training that you want. Rating of Perceived Exertion (RPE) or heart rate are other means of prescribing workouts but the former is entirely subjective and the latter can be affected by a whole variety of external and internal factors often making it unreliable (witness the frustration of athletes trying to use the 80/20 training plan).
Knowing your individual power numbers begins with doing a functional threshold power or FTP test. The FTP test is not perfect and there are many critics of this means of setting power zones. Other power tests have been suggested as alternatives to the FTP test but, barring any of those having been shown to definitively be superior, the FTP test is still the most popular way to do this.
An FTP test is simply a 20 minute maximum effort with the average power over that 20 minutes multiplied by 95% to give your FTP. The FTP is theoretically the amount of power that you could hold for one hour continuously (though I am skeptical that a 20 minute test really shows that). Nonetheless, the FTP is used to set your zones and determines everything about your training.
For example, doing short sprint intervals at 125% or greater of FTP is the best way to become a stronger cyclist. Doing ‘sweet spot’ work at 80-90% of FTP is the best way to build endurance. By combining the two types of intervals you can raise your FTP over time by pulling it up from above and pushing it up from below.
But power meters are much more valuable than just as training aids. Power meters are also incredibly helpful in managing a race.
When racing with a power meter it is much easier to be sure that you are putting out the right effort. Every coach will tell you how important it is to not go too hard on the bike but we all know that for the first part of the bike ride we often feel great and it is all too common that we go too hard even when we don’t mean to especially if we are relying on RPE.
With a power meter, a coach can discuss target power with their athlete and then so long as the athlete doesn’t exceed those targets they are much more likely to stick to the plan and make it to the run without overexerting themselves.
For example, when racing a half Ironman, a well trained, strong athlete should be able to sustain about 80% of their FTP for the bike leg. As a coach I would design a plan for my athlete that would have their average be 0.8xFTP with no surges above 1.0xFTP. An athlete who isn’t as well trained or as strong would have a lower target while a stronger one would have a higher target. Longer races like a full Ironman use 70% of FTP while shorter races like a sprint you may be asked to hold 100% FTP! This percentage of your FTP is referred to as the intensity factor or IF and is reported fractionally (70% of FTP = IF of 0.7).
Another important way that a power meter can help you manage your effort during a race is in ensuring that you are being even in your effort over the course. The best way to ruin your legs on the bike segment of a triathlon is to push too hard on the hills and then try to recover on the downhills. The reality is that no matter how long the downs, you will never adequately recover from the climbs if you pushed too hard on them. This surging on hills is often euphemistically called ‘burning matches’. Burn too many and you will have none left for the run.
The best way to preserve your matches is to ensure that you keep your efforts on the climbs under control and then use the reserved energy to really push when going downhill and on the flats. Fortunately there is a way to record and see this while you are racing but first I need to discuss the difference between average and Normalized power (NP).
I’m not going to go in to a huge amount of detail here but suffice it to say that the difference between average and Normalized power is that average power is simply the average of your power output over a period of time while Normalized power gives a more accurate representation of your true effort given variations in power output due to climbing or sprinting.
You can find more detail on this subject in this article here: https://www.trainingpeaks.com/blog/what-is-normalized-power/ I took this paragraph from that article because I think that it does a nice job summing it up: “Normalized Power is calculated using an algorithm that is a little complex, but in a nutshell takes into account the variance between a steady workout and a fluctuating workout. The resulting value is an attempt to better quantify the physiological “cost” of the harder “feel” of the variable effort. For a highly variable workout, NP can be much higher than average power, where for a very steady workout, NP and average power are equivalent or very close together. A relatively high NP is showing that the workout had a lot of variation, and was harder physiologically than what average power may reveal.”
So how do you use NP to make sure that you aren’t burning any matches on a hilly course? Well, as you just read, when you are on a variable course with a lot of climbing, if you push hard on those hills, that is going to have a bigger impact on your NP than it will on your average power and the gap between NP and average will be large. Ideally, you want that gap to be small no matter how hilly the course. The way that this can be represented mathematically is with the use of the variability index or VI.
VI = NP/avg. power
A well executed bike segment of a triathlon will always have a VI < 1.05.
Here are some examples from my own race history with the outcomes on the run:
IM Indiana, Avg power 181, NP 185, VI: 1.02, 3rd place AG, KQ
StGeorge 70.3 (very hilly course) Avg. power 214, NP 228, VI: 1.07, 7th place AG
IM Louisville, Avg power 192, NP 200, VI: 1.04, PR run, 7th place AG
70.3 WC Nice (VERY hilly), Avg power 181, NP 219, VI: 1.21, close to PR for run
VI was very high because of the 10km climb and the very long descent during which it was difficult to pedal so a lot of zero’s factoring in to the average power. Still, not a good VI!
The key to running well off the bike then is staying within yourself and targeting an appropriate IF but possibly more importantly, making sure that you don’t go too hard on the hills and don’t coast on the downs to ensure that your VI is as low as possible.
I hope that I have made the point that power meters are exceptionally useful tools? You may be wondering now, what kinds are out there and how much do they cost.
Selecting the right power meter
A review of all the power meters out there is beyond the scope of this blog post and I am not going to get in to it. For that I refer you to this excellent buyers guide by DC Rainmaker: https://www.dcrainmaker.com/product-reviews/power-meters
I will spend a bit of time just discussing the basic options that are out there and the pros and cons of each. I will also give you my own recommendations based on my experiences and what I know from chatting with others but I would still say that I am not the expert on this and advise you to do a little more reading before making a decision.
First and foremost, as I discussed earlier, remember that power meters can exist in several different places along the drive train; the pedals, the crank arms, the chain rings or the hub of the rear wheels. For pedals and crank arms, the power meters can be single sided or dual sided. That is to say they will measure the power being applied by both legs or they will measure power from one leg and simply double it (more on this in a short bit).
Here is a quick table listing some of the pros and cons for each type of PM (not exhaustive):
|Pedals||-Available in single sided -Accurately measure the force directly applied to the pedals -Swappable to different bikes||-Not all models as accurate as other PM locations -? durability of some makes -Must configure pedals to correct crank arm length each time changed to a new bike -Cleat may be proprietary|
|Crank arms||-Available in single sided -Accurately measure force applied to pedals||-Cannot swap to different bikes -Not so easy to install -Must be paired with the right components -limited to specific crank arm lengths|
|Chain rings||-Tend to be highly accurate and reliable -Accurately measure force applied to pedals||-Tend to be the most expensive -Linked to specific components -Installation and service a headache -Cannot be moved from one bike to another|
|Rear wheel hub||-Swappable to different bikes||-Must use specific wheel to get power readings -Does not measure force to pedals but force to rear wheel. Power loss across drive train is unknown -Price of wheel added to PM|
I personally have used PMs in the wheel hub, the chain rings and in the pedals and have settled on pedal power meters as the best option for me. I have several bikes and the ability to easily swap my pedals between bikes is a benefit that simply makes pedal power meters an obvious choice. But that doesn’t mean it will be the right choice for everyone.
I would say that in terms of the most affordable power meters, single sided crank arms or pedals are the way to go. A Stages single sided crank arm PM can cost as little as $299 while Favero Assioma single sided pedal power meters are $499.
One thing to note is to be very cautious buying used power meters. You simply will not know what you are getting and you will not be covered by manufacturer warranty if things don’t work the way you expect.
That is pretty much all I have to say on this subject, I know that it was a lot. If you have questions or comments I hope that you will let me know.
Jeff Sankoff is a LifeSport Coach, the TriDoc, an emergency physician, triathlete and USAT and Ironman University certified triathlon coach. He works with athletes of all backgrounds and abilities. To learn more about working with Jeff to achieve your triathlon goals, please contact firstname.lastname@example.org and learn more about Jeff on his coaching page.