The invention of the power meter revolutionized cycling training more than 30 years ago. Then it took another 15 years for power meters to be widely available to amateur cyclists. These days, cyclists can train with power on virtually any outdoor or indoor bicycle. Whether you already have a power meter or are curious about how to train with power, here’s what you need to know to improve your fitness and get faster using a power meter.
What is a power meter
In cycling, a power meter offers a way to directly measure the work a cyclist is performing in real time. The best power meters use strain gauges to measure minute deflections in cycling components as the cyclist pedals. This is why power meters are typically integrated into crank spiders, crank arms, and pedals. We’ll discuss the pros and cons of varying types of power meters later in this article.
Power output is expressed in watts and calculated using the following equation: Power = Force x Velocity. More specifically for cycling, power is the product of torque (force acting on an object to make it rotate) and cadence (pedal speed).
Power meters also reveal the mechanical work produced a cyclist produces, expressed in kilojoules. This is important for estimating energy expenditure. You can generally view kilojoules of work done on the bike to be roughly equal to the calories burned to produce that work. The conversion from kJ to kcal is 4.184 kJ=1 kcal=1 Calorie. Because the efficiency of a human on a bicycle is about 25%, it takes about 4 Calories to produce 1 kJ of mechanical work. So, the Calories required to do 1000 kJ of work would be 250/.25, or 1000 Calories. Although it’s not actually a 1:1 equivalent, it’s close enough for most purposes.
How to increase power output in cycling
As a matter of mathematics, a cyclist can increase power output by generating more torque, pedaling faster, or both. In practice, cyclists decide to push harder on the pedals and/or increase cadence based on several factors. For instance, when pedaling through soft or rough terrain, a lower cadence and higher torque may help maintain traction. During prolonged climbs, maintaining a moderate cadence (80-90rpm) may delay skeletal muscle fatigue compared to mashing heavier gears at a lower cadence (60-70rpm).
How a cyclist generates power also affects speed and acceleration. At times, cyclist need to accelerate quickly, as with launching an attack, initiating a sprint, or closing a gap. When a cyclist is already moving, the most effective way to accelerate is to ramp up cadence, then shift into a harder gear to increase torque, and continue this pattern as speed increases.
Accelerating with a low cadence against a large resistance is also important for some cycling events. Cyclists training for track racing, criteriums, and cyclocross and mountain bike races benefit from specific high-torque workouts.
Power-based Training Terminology
Power meters generates data cyclists can see in real time on handlebar-mounted cycling computers, indoor cycling apps, and various displays. People then upload power data to training software and apps to analyze individual rides and track performance over time. To make sense of all this data, cyclists and coaches reference several common terms, including:
- Average power: a cyclist’s average power output over a given period of time (i.e. an interval, a segment of a ride, or a whole ride), including time spent coasting.
- Normalized power (NP): a weighted average power that estimates what average power would have been if a cyclist didn’t coast or surge.
- Functional Threshold Power (FTP): the highest average power output a cyclist can maintain for 60 minutes, typically determined through FTP tests.
- Training Stress Score (TSS): a single metric that accounts for both intensity and duration to quantify and compare the training load of individual workouts. Read more on TSS.
- Intensity Factor: a measure of the relative intensity of a workout, based on the ratio of Normalized Power to a cyclist’s Functional Threshold Power.
- Efficiency Factor: the ratio of a cyclist’s Normalized Power to Average Heartrate for an activity.
Training Stress Score, Intensity Factor, and Normalized Power are trademarked terms owned by TrainingPeaks.
How and Why to Train with a Power Meter
The best uses for a power meter are to guide your efforts during real-time workouts and competitions, and to track your performance metrics over time. To get the most out of a power meter, it is also important to make sure to calibrate the unit, set the zero offset, and upload the ride data to training software. Here are just a handful of ways training with power can help make you a faster cyclist:
A power meter is a powerful tool for evaluating a cyclist’s fitness. Functional Threshold Power fluctuates throughout the year as the specificity and volume of training changes. Regularly testing your FTP with an 8-minute, 20-minute, or ramp test is essential for making sure your workouts are appropriately challenging.
Using a variety of testing protocols or data from competition files, you can also create a power profile from your highest average power output for 5 seconds, 1 minute, 5 minutes, 20 minutes, and 60 minutes. A cyclist’s power profile can help identify strengths, weaknesses, and opportunities for improvement.
Setting power training zones
Although there are several different power zone protocols, most aim to establish effective training ranges based on your power at FTP or lab-measured power at lactate threshold. By staying within designated power zones, cyclists can focus training stress to accomplish specific adaptations. Protocols range from three to five to seven, and even nine zones. Below you’ll find a commonly used 6-zone system.
Interval training with power
Interval training is an effective way to target training stress by alternating between periods of focused effort and recovery. Coaches design the intensity (power zone) and duration of intervals and recovery periods to target specific adaptations. These can include aerobic endurance, power at FTP, power at VO2 max, anaerobic capacity, and more.
Tracking time-in-zone or time-at-intensity
Although individual efforts within specific training zones are important, meaningful progress results from accumulating time-in-zone or time-at-intensity over weeks and months. For instance, within a single workout, you might perform 3 x 20-minute SteadyState Intervals. These intervals target power at FTP and that workout accumulates 60 minutes of time-at-intensity. Over the course of a few weeks during an FTP-focused training block, a cyclist might accumulate 300 minutes of time-at-intensity.
On a monthly or annual timeframe, time-in-zone provides insights on the balance and distribution of intensity. Polarized training, a protocol that encourages a roughly 80/20% split between easy/hard training intensity, relies heavily on tracking time-in-zone.
Tracking training load
Effective training must balance training stress with adequate recovery to produce positive physiological adaptations. Consistently uploading power data to training software provides a detailed picture of an athlete’s total training workload.
TrainingPeaks software aggregates daily workout data into its Performance Manager Chart. It charts daily TSS, a metric based on the intensity and duration of each workout. Individual data points are then used to create three training metrics: Acute Training Load (ATL), Chronic Training Load (CTL), and Training Stress Balance (TSB).
- Acute Training Load (ATL): A weighted average of the past 7 days of TSS. This number indicates the level of fatigue generated from recent training.
- Chronic Training Load (CTL): A weighted average of the past 42 days of TSS. It is sometimes thought of as an athlete’s “fitness level”, but it may be more accurate to think of it as “the workload an athlete has been sustaining”.
- Training Stress Balance (TSB): Yesterday’s CTL minus yesterday’s ATL. This value is considered an athlete’s ‘form’, or a prediction of an athlete’s readiness to perform. If yesterday’s workout was hard in comparison to an athlete’s current fitness level, TSB goes down for today. You’re likely to feel fatigued. Following a few days of easy riding or rest, TSB rises and you’re likely to feel energized and ready to train or compete.
These are not the only metrics used to track training load, but they are among the most common.
Training with Power vs. Heart Rate
Power meters are the gold standard for prescribing training and tracking performance in cycling. However, heart rate data and perceived exertion both provide valuable context that makes power data more meaningful.
Heart rate monitors provide information on your body’s response to exertion. A power meter is a direct measure of the work you are doing in real time. Heart rate is a lagging indicator of your body’s response to that work, in that it takes time for the effort to be reflected in heart rate data.
Athletes can train effectively using heart rate alone, but for several reasons we prefer training with power when possible. Heart rate can be affected by environmental conditions, core temperature, hydration status, fatigue, psychological stress and excitement, medications, stimulants like caffeine, and more.
Nevertheless, in normal conditions heart rate responses typically fall within predictable ranges associated with given power outputs. For instance, you may know that on a normal day, climbing a hill at 250 watts will likely elicit a heart rate of 140-145 beats per minute. Heart rate responses that are abnormally high or low cause athletes and coaches to look further into the data and the athlete’s behaviors.
When used in conjunction with a power meter, heart rate data provides insights on the body’s response to producing a given workload. Efficiency Factor (ratio of Normalized Power to average heart rate for a given period) is one example of this. A higher EF means you can produce more power at the same or lower heart rate. This indicates improved fitness and predicts the potential for improved performance.
Training with Power vs. Perceived Exertion
Along with heart rate, perceived exertion provides insights into how strenuous a given power output feels to a cyclist. As with the example above, climbing a hill at 250 watts might normally feel like a 5 on a 0- to 10-point scale of rating of perceived exertion. Stress, fatigue, poor sleep quality, or various other factors can make that same power output feel like an 8/10 today. In contrast, as you gain fitness during a season, 250 watts on that climb could feel easier, and a sustainable RPE of 5/10 could subsequently associated with a power output of 275 watts.
RPE is also the best way to gauge intensity during competitions. As conditions change, races get longer, and fatigue builds, power and heart rate zones become less reliable. But you still know what an RPE of 6 out of 10 feels like and that 6 out of 10 is sustainable. Read more about using RPE in training and racing.
The mark of a skilled athlete is learning to use technology effectively while also reducing your dependence on it. In normal training or racing conditions, a skilled and experienced athlete can often accurately identify power and heart rate values without even looking at a display.
Types of cycling power meters
Ulrich Schoberer invented the original cycling power meter in 1986. The SRM (Schoberer Rad Messtechnik) gained traction with Olympic teams and professional cyclists in the early 1990s and was the first power meter available to the public. More than 30 years later, cyclists have many more power meters to choose from. Power can be measured several ways on outdoor and indoor bikes. If you are considering a power meter, here are the strengths and weaknesses of different types:
This is SRM’s original location for power measurement, and is still Uli’s preferred method for its accuracy, consistency, and durability. Other companies with crank spider-based power meters include SRAM Red AXS, Quarq, Power2Max, and Rotor. One downside to spider-based power meters is that they are difficult to transfer from bike to bike.
Instead of placing strain gauges inside the spider, these power meters measure the deflection of one or both crank arms during the pedal stroke. Crank arm power meters are available from Stages and 4iiii. When using a single-arm power meter, the power value from that side is doubled to display your power output. This is reasonably accurate, but not as accurate as measuring on both sides. On the positive side, single-arm power meters are among the most affordable options available. Some athletes purchase 2-3 to train with power on multiple bikes, rather than moving a power meter.
Pedal-based power meters are popular because of their convenience and transferability. Companies offering pedal-based power meters include SRM, Garmin, Wahoo, and Favero. SRM and Garmin offer both road and MTB/gravel versions, and most manufacturers offer models with either single or dual side measurement. Some models feature the ability to transfer the pedal spindle between road and MTB pedal bodies, too. Although the accuracy and consistency of power measurement is good, keep in mind that pedals are a vulnerable component. They can stand up to a lot of abuse, but you’re still likely to slam them into rocks or pavement.
Smart Bike and Smart Trainer
The explosion in indoor cycling apps (i.e. Zwift, RGT, Rouvy, BKool, FulGaz) was partly driven by the widespread availability of electrically-braked ergometers built into indoor trainers and indoor cycles. These app- and headunit-controllable ergometers earned the moniker ‘smart trainer’ and ‘smart bike’. Popular brands for smart trainers include Wahoo, Tacx, Elite, and Saris.
Wahoo, Stages, and Wattbike are leading brands for performance-oriented smart bikes. Athletes can also find the ergometer functionality of smart bikes in some home fitness and gym-based indoor cycles, including versions of Peloton, Echelon, and Nordictrack indoor cycles.
CTS Power Meter Recommendations
CTS Coaches have been working with power meters since the early days of SRM. We used Powertap hub-mounted power meters when they existed, and we currently work with athletes using all types of power meters. Our top choice is a spider-based power meter for accuracy, consistency, and reliability. Our next choice is a pedal-based power meter because the accuracy and consistency are good and they are easily transferred between bikes. Crank arm power meters are good value choices. And smart trainers and smart bikes are great additions to anyone’s arsenal of training tools.