Learn All About Power Meters

Traditional Technology    Watts Are Better    Watts Defined    Great For Any Rider    Show And Tell


By now you've probably seen friends riding with fancier-than-normal computers and strange new hubs or cranks on their bikes and found out they're riding with power meters. You may also have overheard cyclists and coaches talking of "power" and "watts." Or maybe you've read of the wattage output of cyclists like Lance Armstrong. We're not surprised. Power measurement is the most objective, reliable measurement of cycling output, and we're here to explain how it works and help you decide if you should join the most exciting revolution in cycling since shifting brake levers.

Traditional Technology
If you've ridden for a while, you've probably tracked rides with traditional technology like cyclo-computers. These became common in the early 80s and gave rise to structured training, allowing cyclists to measure speed, distance and later cadence. Instead of just, "going out and riding," riders could now track their progress on a set course to measure their fitness. However, factors such as wind and grade affected speed and were unmeasurable (except in the most controlled conditions), and provided no output of the objective effort needed to reach a given speed, so efforts could not be accurately compared.

Heart Rate Helps
Heart-rate measurement revolutionized cycling training when it became commonplace about 20 years ago. With it cyclists could measure their body's effort instead of only the symptoms (the speed reading on their cyclo-computer) of that body's effort. However, heart rate was a measurement of just one of the body's muscles, not an account of the body's final resulting pedal output. It has a lag in catching up to the muscular effort of pedaling. And, while heart rate increases at a rate proportional to pedal power in a controlled lab environment, it rarely does so on the road or trail. Heart rate also has high susceptibility to temperature, fatigue, altitude, caffeine intake, time of day and more, making it an imprecise measure of performance on a given day and a limited tool for comparing multiple workouts.

Power Arrives
Watts are accurate and objective!Power meters, which have now become almost standard equipment for professionals and any cyclist or triathlete interested in improving, solve cycling's subjective problem, the inability to account for outside forces. They track wattage, an objective, accurate measurement of energy output in the face of all resisting forces, to measure fitness and effort in a way that no heart-rate monitor or basic cyclo-computer can. And, the resulting data (power meters include software for downloading and analyzing ride data) is essential for effective training as well as informative and fun—even for cyclists without specific goals.

Power is the most objective way to measure cycling output. A power meter measures cycling effort in much the same way that the 45 pounds stamped on the side of a weight lets you know how much weight you lift. Would you go to the gym and squat an unknown amount of weight in the hopes of perceiving a training benefit? Probably not. With power, there is no gray area.

Another example: Look at the following heart rate versus watts training scenario. You've just done a tough 2-hour ride that included 3 sets of 4 by 1-minute intervals. The intervals felt hard and your heart seemed to get within 5 beats of time-trial pace on each one but couldn't go any higher. You rode the rest of the ride at 17 to 18mph average pace. Were you riding hard or hardly riding? You can't tell from heart rate yet you'll know for sure if you ride with a power measurement device. Read on and find out why wattage should be part of your riding plan.

Watts Are Better
Watts are better for a number of reasons, including:

  • Watts are a measurement of all forces acting against you.
  • You can compare your wattage on a given ride to your wattage on any other ride. 
  • You can compare your efforts to those of any other rider in the world.

Watts are objective, not dependent on the varying factors of your body or the weather. If you held 305 watts for 30 minutes on April 8, and then you churned out 318 watts for a 30-minute period a month later, you know you are improving.
Click to enlarge!
Similarly, you can match 10-second maximum wattage or threshold wattage with any other rider in the world. Do you sprint like Mario Cipollini (few people do)? How does your power rate over a minute effort? When it comes to hour efforts are you capable of excellent power or do you just maintain the pace of a rider in the early season?

Because wattage output is related to body weight, the gauge used when comparing your wattage to the number other riders produce is your wattage output per kilogram of body weight. Most software that's included with power meters gives you the data so you can find output per kilogram of weight listed when reviewing your ride data too—no calculations needed on your part (body weight in pounds divided by 2.2 will give you kilograms). Once you have this number you can compare it to get an apples-to-apples comparison and see how you're doing related to other cyclists (chart). And this will give you an idea what level you need to get to to improve.

Watts Defined
It should be clear by now that we can't say enough good things about using watts to track and improve your training. But, how do we get this valuable objective measure of your efforts against all the forces acting against you? The watts measurement takes into account the sum of all forces acting against your movement including aerodynamic drag, weight and friction, to provide an accurate measurement. And this measurement isn't thrown off by variables such as temperature, lack of sleep, altitude, coffee, amount of food eaten, and rider body size (as are heart-rate measurements). 

Actually, it's helpful to compare heart rate measurement a bit more. To give an example, a 20-minute average heart rate of 159 beats per minute (bpm) on April 8, followed by a 162-bpm effort on May 8 does not necessarily reflect improvement. Your time on a familiar course could have been faster in April with a lower heart rate. But even a faster time doesn't necessarily reflect a better effort. Other factors including wind, which provides up to 90% of a cyclist's resistance even on a windless day, could have been much stronger during your slower effort. To get an accurate understanding of the effort you put in you need to be able to measure power.

Cycling power defined!Power, or the energy produced in a given time frame, is scientifically expressed as a measure of intensity known as a watt. A watt is equal to 1 joule per second. A joule is the derived unit needed to accelerate a mass of one kilogram, one newton of force over a distance of one meter. So when you look at the wattage field of your power meter, you're seeing the total amount of energy needed to move your body's mass (x number of kg) against the resisting factors in a given moment. You're seeing an immediate, scientifically accurate measure of your effort.

Measures Short Efforts
Power measurement's superior feedback capabilities are most noticeable when trying to measure shorter intervals. Take a 30-second interval as an example. Your goal might be doing 30-second intervals at an anaerobic pace. The instantaneous feedback of a power meter makes that possible. Within seconds of starting, you'll see the measurement enter the given zone, for example 450 to 500 watts. The power meter's constant, immediate feedback ensures that you'll stay in the correct zone (assuming your legs and lungs are capable of it). 

Watts measure short, powerful intervals and sprint efforts!The same intervals would be nearly impossible with a heart-rate monitor because of heart-rate lag. As your muscles begin pushing at a difficult level of resistance, it takes your heart a while to realize that it needs to supply oxygenated blood to the area in question. By the time you've completed 30 seconds, your heart rate might still be 3 to 15 beats below your time-trial heart rate simply because it hasn't caught up. So how do you know you completed the interval at the correct intensity level? You don't. You could have ridden at a much easier threshold level, hammered along at an excessive sprint pace or, most likely, mixed the two.

Speed is also an inaccurate measurement of short intervals because even seemingly negligible wind and grade changes make huge differences in the power needed to move your body through space.

Long Efforts Are More Accurate
Long efforts can be measured more precisely with a power meter, too. If your aerobic power zone is between 180 and 220 watts, you can target 200 watts and hold that pace for hours on end. Riders without power meters typically go too hard up even the smallest grades. The surges above sensible pace often throw off their workout. You won't make that mistake as you climb at a steady 200-watts. Riders without power meters also often lose or waste training time by riding too easily downhill, often coasting. With a watt meter you'll hold the correct wattage—even downhill. These variations in power add up over time and can make the difference between a hard aerobic ride and an easy one.

The total ride effort expended over time can be measured in kilojoules; and a hard 4-hour aerobic ride could easily measure 2,500 kilojoules, while an easy ride of the same duration could rack up 1,600 to 1,800 kJ. You'd have no way of knowing this with a heart-rate monitor or speedometer but your power meter allows you to pinpoint this level of exertion and train and ride more effectively.

The power meter's measurement of exertion also helps you optimize your nutrition. One kilocalorie is equal to 4.1 kilojoules, so if you do a 2,000kJ ride, that would be equivalent to just under 500 kilocalories. But, on a bike, the body is only about 25% efficient, so if you exert 500 kilocalories of energy, you burn about 2,000 kilocalories of fat and glycogen. This virtual 1-to-1 correspondence between cycling kilojoules and calories, makes the kilojoule counter on your power meter a great guide if you’re trying to lose, gain or maintain a healthy weight.

Great For Any Rider
Any rider can benefit from power measurement!Calorie measurement ability is another reason we think a power meter is a great tool for any rider. Simply put, the power meter is a more objective measurement of your body's effort than almost any other tool. Because you know how many calories you've spent, you can adjust your intake accordingly. And, when you realize how much effort it takes to burn 50 kilojoules, the equivalent of one Oreo cookie, you'll think twice about eating it. You now have the artillery to win your personal battle of the bulge.

We're convinced that riders of all abilities will also enjoy the ability to pick their pace at any time. You might not have specific racing or training goals, but you'll love the way you can pick a perfect pace over your favorite killer climb. You won't go too hard, only to explode spectacularly; you won't ride too easy and wonder if you had more in the tank; you'll pick a pace perfectly suited to your ability.

A power meter also shows you exactly what you need to do to improve to whatever riding level you aspire. Have a hard 20-minute climb or crosswind stretch on your favorite group ride? If you notice you are consistently getting dropped in that section you can analyze the wattage you need to hang tough. You'll be able to recreate this wattage on any training ride regardless of terrain or riding partner and you'll make gains faster than if you were to simply "go out and ride" or measure your efforts with less effective speed and heart-rate data.

Finally, you'll be able to track your fitness and improvement over a wide array of new levels. If you've enjoyed measuring your average speed on your favorite courses, you'll love being able to measure effort, calories, time in various zones, the intensity factor of the ride and much more.

Show And Tell
Great features that come with your power meter are the unit's memory and the software you use to download, save and review your ride data. Once downloaded, it's the ability to see so many forms of your personal cycling output in many easily refined stat tables and graphs that makes the power meter an unrivaled tool. We've spoken about the numbers that you see as you ride, but it's the quantification that you see after a ride that let's you learn about your abilities and the courses you ride. Most power meters come with software to track your rides. Some programs are very good, others are not as effective. There are separate programs you can buy if you're not happy with what came with your power meter. We're happy to recommend a program if you have any questions.

"Reading" Each Workout
Click to enlarge!To give you an idea of how you might use this software, let's start with data from a single workout. On that screen you'll be able to view power, heart rate, speed and cadence as the workout or race progressed. Most programs will show you your highest power output for given time limits like 5, 10, 20 and 30 seconds as well as 1, 2, 5, 10, 20 and 30 minutes. 

You can also track a custom time period by selecting the period of time and, as you mouse over that area, your scores change to reflect the chosen time period. Once you have a selection you like, you can name it. In this way you can chose a series of 3-minute intervals, a short 39-minute crit or a hard 4+ hour race.

The single workout screen also shows you your totals for the ride including your effort score in kilojoules. Your totals may also include measurements of intensity factor (IF) and your training stress score (TSS). The former is the ratio of your average power (excluding time spent not pedaling) to your threshold pace, which is similar to your time-trial pace. By calculating how much time you spent under, at and over your threshold pace you can get the IF, which will help you compare the difficulty of different workouts on a level playing field.

TSS takes IF into account to provide an even better big-picture measurement of training stress. By taking IF and duration into account, TSS can be used to quantify your overall training load. By then gradually increasing TSS for several weeks and dropping it during rest weeks, you can pinpoint overload training like never before. Or, if serious training isn't your goal, you'll be able to gauge fatigue like never before. If you have trouble sleeping or find yourself snapping at your relatives, a quick check of TSS will show you if overtraining is to blame.

The Big Picture
Click to enlarge!With the power meter and software you'll also be able to graph all the measurements we've spoken of in countless ways. Chart your training stress and time by week, measure your mean maximal power for the last 28 days, or compare average power to weight. These are just a few of the graphs that you can create to get a better picture of your cycling efforts. Painted with power measurement you'll have a brilliant illustration of your cycling and not a murky, unintelligible image, which is the key to fast improvement.
  
Further Use
There's a lot more that you can do with a power meter: you can elaborately track your training progress and build a focused training plan based on that data, you can figure out how much energy you can expend before you need to eat in long races, you can use the power meter as your own version of a wind tunnel and hone your aero position to perfection. We could go on forever about the ways to use a power meter but we'll stop for now. If you'd like to learn more about these amazing cyclo-computers, come in and talk with us. We're happy to talk about power and show you our selection of power-measurement tools. Welcome to the wonderful world of training by watts!

Traditional Technology    Watts Are Better    Watts Defined    Great For Any Rider    Show And Tell