What is a power meter in cycling?
Let’s start with the basics. Cycling power meters are devices typically attached to the bike’s pedals, crank spiders, crank arms or rear hub. They use strain gauges to measure the torque being applied to the bike’s drivetrain, which reveals how much work the cyclist is doing in real time. The power data is then transmitted to a bike computer, which displays the power output and stores the data for later analysis.
Power output is expressed in watts and it’s made up of torque and cadence. Power meters also reveal the mechanical work a cyclist produces, which is expressed in kilojoules or kilocalories. As you can imagine, having precise data about how much power you generate on the bike and how many calories you burn is invaluable for planning your training, racing, and even diet. But before we get deeper into these topics, let’s go over the terminology.
Power meter training terminology
Understanding the basic terminology used by other cyclists and coaches will help you make sense of the numbers your power meter provides. Here are the most commonly used phrases and terms.
- Cadence: The number of times a cyclist’s pedals rotate per given time interval, typically measured in revolutions per minute (RPM).
- Torque: The force applied to the pedals to turn them, measured in Newton-meters (Nm).
- Average power (AP): This is used to describe a cyclist’s average power output over a given period of time, including time spent coasting. The period of time could be an interval, a segment of a ride or the whole ride.
- Functional threshold power (FTP): The highest average power output a cyclist can maintain for 60 minutes.
- Power zones: A range of power outputs that correspond to different training intensities, typically expressed as a percentage of FTP.
- Normalized power (NP): This is a TrainingPeaks trademarked term. It is a calculated power value that estimates what the average power would have been if a cyclist didn’t coast or surge. This is why it became more popular than AP.
- Intensity factor (IF): This is a TrainingPeaks trademarked term. It’s a measure of the relative intensity of a training session, based on the ratio of NP to a cyclist’s FTP.
- Efficiency factor (EF): This metric quantifies a cyclist’s efficiency in converting energy into forward motion. It’s expressed as a ratio of a cyclist’s NP to the average heart rate for an activity.
- Training stress score (TSS): This is a TrainingPeaks trademarked term. It is a metric that uses both intensity and duration to quantify and compare the training load of individual workouts.
- Acute training load (ATL): This is a TrainingPeaks trademarked term. It’s a weighted average of the past 7 days of TSS.
- Chronic training load (CTL): This is a TrainingPeaks trademarked term. It’s a weighted average of the past 42 days of TSS.
- Training stress balance (TSB): This is a TrainingPeaks trademarked term. This value predicts an athlete’s readiness to perform. It’s calculated as yesterday’s CTL minus yesterday’s ATL.
- Fitness / Freshness: This is a Strava formula that predicts an athlete’s readiness to perform, similarly to TSB.
