• Jason Lentzke

Yes, You Need a Power Meter

If you’re reading this article there’s a good chance you’re a triathlete. If that’s the case, it’s highly probable that you’ve heard of the terms power meter and wattage. What is a power meter? It’s an unnecessary, intimidating, expensive piece of equipment that produces complex data that can only be analyzed by a rocket scientist or an expensive coach using unusual computer software. Not exactly…

What is power?

Power is defined as the rate at which energy is transferred. Essentially, a power meter is a device measuring the force that you’re applying to the pedals. Power meters can be located in the hub of your rear wheel, the cranks of your bicycle or even attached to your pedals. Your power is an expression of work rate and a watt is a measurement of power. One watt is expressed as 1 joule per second. A joule is the measurement of work, equal to about .25 calories. A kilojoule or kj is a product of force and distance. The total kilojoule expenditure at the end of your ride is referred to as work. To understand the concept of power, you simply need to understand the relationship between how hard you work and the rate at which the work is completed. Pretty simple!

OK, I think I’m going to buy a power meter. How do I use it?

If you can use a Garmin, you can easily use a power meter. Read the operating instructions carefully and inquire with your bike shop, coach or training partners as to how to install and calibrate your power meter. Most of the power meters on the market have informative how-to YouTube channels. It is essential to calibrate your power meter before every session to ensure accurate power measurement. Once your PM is calibrated with your head unit (Garmin, Polar, etc) you’re ready to ride. For the first couple of rides just get to know the numbers and observe how they change as your effort fluctuates. Glance down and compare your rate of perceived exertion (RPE) and heart rate (HR) with the wattage you’re seeing on your head unit. You may also want to adjust the data fields on your head unit/Garmin to display the metrics of your choice.

Within just a few rides you will become much more self-aware and your rate of work and perceived effort will be better understood. You’ll soon come to realize that a watt is a completely objective unit of measurement. Your HR is subjective and can be affected by outside influences like overexcitement, dehydration, lack of sleep, excessive heat, etc. Your HR monitor may not be telling you how hard you’re truly ricing and your watts never lie.

Functional Threshold Power

Once you’ve gotten comfortable with your power meter it’s time to determine your functional threshold power (FTP). Testing and establishing your FTP will enable you to establish effective training and racing zones. It can be beneficial (but not necessary) to test your FTP every 4-6 weeks to monitor your fitness and adjust your zones accordingly. Performing the test is fairly simple if you have a stationary trainer or a quiet, flat stretch of open road. Although a 60 minute test is ideal, a 20 minute test will suffice. Pacing and executing an FTP test is an art form. The more you do it, the better you’ll get. I like to use the following testing protocol on our athletes:

1. To start, warm up well over a 20-minute period and include some high cadence work.

2. Ride 5 minutes hard aiming for a tough, but sustainable effort. I like to ride @ 70.3 power for this effort.

3. Ride easy as recovery for 10 minutes.

4. HIT IT! Do your official 20-minute test. Your first 5 minutes should feel difficult but sustainable. Assess your effort every 5 minutes and make it harder if needed. Maintain your race cadence (85-90) and make your last 5 minutes an “I want to quit this sport!” type of effort.

5. Calculate your FTP by taking 95% of your average normalized power produced for the 20-minute duration.

How to Race With Power

Once we have established your FTP we can determine your training and racing zones. You’re probably familiar with HR training zones. Power zones are similar, only much more objective. On race day, speed is an irrelevant metric to monitor. Let your HR and power hang out in your prescribed zones and allow your body to perform. If you’ve exceeded the physiological demands of racing in your training and race preparation, your power and HR will reflect that. Follow the dynamics of the race and use your power meter as a weapon. Your power meter provides data that prevents you from having to rely on your emotions alone. Particularly in 70.3 and Ironman-distance events, it is critical to know your limits and keep your emotions in check if you want to run well off the bike. You don’t want to be the Ironman athlete walking on the run course bragging about their 4:45 bike split…

That being said, it’s important to remember that you shouldn’t be a slave to your data as you race. Dr, Philip Skiba said it best, “One of the most useful aspects of working with power and pace is your ability to comprehend how your perceived exertion correlates with the objective data coming from your power meter.”Pacing with a power meter on race day is quite simple as long as you know your limits. A well-prepared athlete knows their body well and has a realistic goal going into their key race. Below are two excellent estimated pacing guidelines created by Dr. Philip Skiba.

Note the power ceiling and averages for 70.3 and Ironman distance events. Exceeding the recommended values will lead to a catastrophic run. Ultimately, every athlete’s experience, training load and physical ability will dictate their pace, but these guidelines are a great place to start. By referring to Skiba’s charts you can begin to incorporate effective pacing and race simulation workouts into your own training and racing.

Kilojoules > Kilometers

Derick Williamson wrote an excellent article a few years ago that highlighted the importance of training with a targeted kj expenditure vs. a specific mileage or ride time. I encourage you to read and bookmark his article but I will reemphasize and paraphrase what he highlighted.

As I mentioned earlier, the total kilojoule expenditure at the end of your ride is referred to as work. Once you’ve calculated the total work demand of the bike leg during your race, you can much more precisely plan the overload and the progression you’ll need to achieve for success.

For example, a professional male needs to average about 3.8-4.2w/kg (watts/kilogram) and a professional female will need an average of about 3.3-3.7w/kg to be a realistic competitor. Note that there are always outliers (uber bikers) but they typically fail to meet expectations on the run. Of course, there are always exceptions!

If a male AG athlete wants to be in contention for Kona Qualification, he most likely needs to ride @ 3.2 w/kg for 112 miles. At a race weight of 75kg and 5-hour target bike split, that would require an output of 230-35w over 112 miles. Using a simple formula I can determine that this athlete needs to be prepared to expend 4230 kj during the 112 mile bike leg.


(total time in seconds x avg power) ÷ 1000

(5 hours x 60 min) x 60 seconds= 18,000 seconds

18,000 seconds x 235w = 4,230,000 ÷ 1000= 4230 kilojoules

During preparation for an Ironman distance event, that Kona-conteding AG athlete will ride long almost every weekend for the 16 weeks leading into the race day. The athlete may ride up to 130 miles on a training ride during their peak volume. Let’s say that during one of those very long rides he (a 75 kg male AG athlete) joined a few friends and rode hard, attacked, climbed and kept the effort honest while on the front. He ended up averaging over 21 mph for the ride and was pretty proud of himself when he uploaded the data to TrainingPeaks and Strava. However, despite the overload of miles the athlete didn’t meet the physiological demands of his target Ironman ride time. According to the Garmin file, he was 500kj short of the 4230kj target expenditure. I guess he did more wheel sucking and soft pedaling than he thought! Because of this, he’s not as prepared as he thought he was and won’t be prepared to run well off the bike if he continues this trend each weekend. As you can see, time, distance and even HR can be misleading when it comes to the actual physiological demands of racing. Training for long course triathlon utilizing your target kj expenditure allows an athlete and coach to strive for a quantitative and precise training metric.

It should be noted that the formula used to determine estimated kj expenditure does not take your bike position and setup into account; ie. how slippery you are in the wind. A proper fit that allows the rider to maintain an aero position for the the entire duration of the bike leg is essential. Your bike position and equipment setup may save you watts, so you may end up riding faster than predicted all while banking energy for the run.

OK, I get it. But, I’d rather buy some new wheels.

Having spent years in the bicycle industry and having a sound understanding of triathlon culture, I understand the temptation and desire to spend your money on a nicer bike or more aerodynamic accessories to improve your bike split. After all, as triathletes we spend as much of our race on the bike as swimming and running combined. You need to spend more to go faster, right? Not so fast (literally). As written in Jim Gourley’s book, Faster, “Your bike typically makes up 30% of your total aerodynamic resistance, less than 15% of your total bike/rider mass, and 0% of the power generation.” I challenge you to spectate any local, national, Challenge or Ironman-branded triathlon. Observe the bikes that you see in transition. There are plenty of “fast” looking bikes being ridden incredibly slowly. Don’t be that triathlete. A power meter is the best piece of training equipment that money can buy. Invest in your engine by investing in a power meter.

I composed this article to entice triathletes who may be on the fence or have disregarded the entire concept of training with power because “it’s not for them.” Power meters can benefit any athlete who is committed to their training and has a desire to train smarter and cross the finish line faster.

The power meter market is flooded with options and it’s important to choose wisely. Feel free to email me or check out DC Rainmaker's latest Power Meter Buying Guide. If he wouldn't buy it, you shouldn't buy it!

#powermeter #ironman #triathlon #SRM #Quarq #power2max #cycling


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