The benefits and limitations of Cycling Power Meters
Training with a cycling power meter brings more precision to training and adds another way to view your cycling output. Power, described in watts, tells you in simple terms how fast you’re spinning the pedals against how much force you’re placing on each pedal stroke. High power outputs can be produced with a slow cadence and high amounts of force or with a fast cadence and lower amounts of force. In any cycling race, both low and high cadences are required but for the majority of the race an optimal cadence is used to produce the highest power output for the duration of the event. Power has many benefits from analytics to training but at the same time there are some limitations, such as the reliability of the meter itself.
The benefits of cycling power meters
Training with a Power Meter
When training, a power meter brings in detail how hard you’re working at any given time, whether climbing a hill or pedaling a flat road. One of the big benefits of power is the ability to get into a training zone right away. For example, while on a climb, if targeting sub threshold or FTP power, you can get into the intensity immediately while things like heart rate and perceived effort take a moment to catch up. This allows you to get the most out of the effort and your day. When training indoors, power becomes even more of a tool as it keeps you focused on precise intervals, and structured workouts, efforts which are harder to complete outdoors due to weather or terrain. Power meters also give insight into fatigue, such as when you can’t achieve the power goals for the day. This is valuable because at times heart rates will respond to the training zone while power may be low, signifying muscle fatigue and the need to back it off for the day.
Analyzing Power Data
The analytical data you get from a power meter is the next biggest benefit. As we will discuss, there can be some technical issues with power meters in general, and that can affect data analysis but in general terms, power readings and averages allow you to view trends over time. When you feel fresh in training, chasing Strava KOM’s or in fast group rides, power readings from these days can tell a story. Analyzing 5–20-minute peak power outputs for certain training rides can give you an idea of whether your getting stronger for those time durations or not. Compare the power of the day with how you felt to gain more insight on the ride. Analyzing weeks, months and even seasons of peak power averages against each other is another good way to view strength gains and losses for a specific period. Let’s say you compare the base season of your current season - January through march to the same time the year prior. This lets you know whether your power averages, such as your 20–60-minute averages are up or down compared to the previous base season. You can then dive in further to see why, analyzing changes in training that worked, what didn’t and more.
Pacing in a Race
Using power to pace in a race will vary by event type. It’s hard to use power on a technical mountain bike course. If you’re looking at the power meter you may not be able to dodge the tree or rock coming at you, plus technical terrain and drops can cause power spikes. But if within that same race there is a long steady hard packed dirt climb, then a power goal may be a benefit. A time trial on the bike is one of the best places for a power goal due to its simplicity. If you’re racing a flat ten-mile time trial, knowing It's going to take around 30 minutes, and you also know your current peak power output for 30 minutes, then that peak power average can be used as a great guide and a good place to start the race.
Limitations of Cycling Power Meters
Reliability of the Power Meter
The reliability of the power meter is one of the biggest limitations. All power meters are manufactured differently and measure power in a different way. No two power meters are the same, from those on the bike to your smart trainer at home. In this article by bike tech guru, DC Rainmaker, he reviews the inconsistencies with the Shimano R9200P Power Meter. This is just one example, but power meters have had inconsistencies over time from pedal-based issues to the old hub-based power meters which were not as reliable due to wearing chain rings and chain stretching. A way to find the inconsistency of the power meter is to test them. Here DC Rainmaker provides a good guide to testing power meters and analyzing the results. When it comes to analyzing power data, any inconsistency will skew the results, making it hard to see gains or losses. One of the most common inconsistencies isn’t with any individual power meter but when a cyclist will train with multiple different power meters throughout a season and on varied terrain. This makes it harder to see the true trends throughout the year.
Power is a Relative Measure of Fitness and Fatigue
While power is a great tool, it’s still relative to what’s happening inside the body. Heart rate, perceived effort, leg feel, motivation and form provide additional feedback, on top of power, to provide a full picture on how you feel for a given day or period. This bio feedback along with power can be referred to as the dashboard in training. Like getting in your car, the dashboard tells you what’s on and off and that will tell you whether to push through training or back off and rest. A good rule of thumb is to press on with training when 1-2 things are off, like low motivation and a lower responding heart rate but power, feel and form are right on. But when more than 2 things are off such as additionally having low power, and or bad form on the bike, you then back off the goals for the day.
Using power exclusively can be a true limiter. There are going to be days where you feel good and all things, including heart rate, perceived effort and more are all aligned and responding well in the warmup phase. You then get into an effort and follow power exclusively, nailing the FTP or sub threshold effort with a low perceived effort and heart rate 10-15 beats lower than normal. Let’s even say legs feel good and you can work the FTP efforts all day and for any duration. These are situations where you need to question whether you’re working hard enough. These are breakthrough moments where if relying on power alone, you can miss. This is why it is important to sync heart rate with power zones when fresh, so you know where you stand as far as working a Sub LT power or FTP number and heart rate range. This way you recognize when things are responding and easy and therefore need to up to intensity, surpassing the original power goal.
Cycling power will always measure higher on a road bike and on a road. There is little give between a road cycling tire, inflated to 100 PSI, on asphalt, along with the bigger gears of a road bike. On the flip side, an off-road bike has bigger tires with more squish and that squish, along with the give between an off-road bike tires and dirt, produces a lower power reading on your monitor. It’s important to realize these nuances with power while analyzing it as there is more to power than just a number. Power is a great tool, but it is only one part of the full picture in training.
Mike Schultz, CSCS