Power meters are an excellent way to fine-tune your training and gauge your pace during a race. Now that the cost of power meters has dipped into the $200–$300 range, they are more widely available to cyclists than ever before.
The problem is that these extra metrics and new data can be confusing and not particularly useful if you don’t know what to look for. Whether you’re just getting started with a power meter or wondering whether or not it’s worth the purchase, this guide will take you through the basic measurements a power meter provides and how this data can help you on the bike.
For cyclists, power is the amount of energy you produce at any given moment. A power meter measures energy expenditure in watts. While heart rate and miles-per-hour metrics for pacing can be skewed by variables such as terrain, wind, fatigue and cadence, measuring watts is considered a more accurate way to judge the intensity of your ride because it eliminates these variables.
Once you know the number of watts you can maintain over a specific distance or period of time, your race-day pacing will become as simple as staying within your wattage range.
Watts per Kilogram
Watts per kilogram of body weight is an even more accurate way to determine how much power you are producing. Because it takes your body weight into account, watts per kilogram explains why a higher wattage doesn’t always equate to who is the fastest cyclist.
For example, a 200-pound cyclist producing 390 watts (4.3 w/kg) isn’t going to be faster than a 155-pound cyclist who can produce 330 watts (4.7 w/kg) over the same distance. While the difference in watts per kilogram may not be as noticeable when riding in a group of cyclists on flat roads, it is more noticeable when cycling uphill when aerodynamics play less of a factor.
To calculate your power-to-weight ratio, here’s what you’ll need to do:
- Take your average power from a 20-minute time-trial effort.
- Convert your body weight from pounds to kilograms.
- Divide your average watts by your body weight in kilograms.
In general, a top pro cyclist competing for the yellow jersey at the Tour de France will have an power-to-weight ratio of 6.5 watts per kilogram or higher, while a cyclist who is a beginning racer or century rider will usually be around 2.8 watts per kilogram.
Like average speed over an entire ride, average power is the average number of watts you produce from start to finish. While it isn’t so important to know your average power during the ride, it can be a good metric to look at after a ride to gauge how hard you’ve worked. Keep in mind that average power numbers also include coasting and downhills, so it may not be the best at determining your current level of fitness.
Threshold power is also commonly referred to as critical power. Used most often for training zones and pacing during a race, your threshold power is the average number of watts you can produce over a one-hour time-trial effort. This article explains how to calculate your functional threshold power (FTP) and how to determine your training zones for workouts.
Normalized Power (NP)
While average power is a good indicator of how hard you’ve worked during a ride, normalized power is a more accurate way of gauging your fitness. Normalized power estimates the power you could have sustained for the entire ride without variables such as time spent riding downhill and coasting up to stop signs or red lights, which are included in average power metrics.
Keep track of your normalized power numbers to track fitness improvements during the cycling season or from year to year.
Training Stress Score (TSS)
Since most cyclists repeatedly train on a handful of routes, one way to compare like training rides with each other is by analyzing your training stress score. The TSS score measures intensity and duration, or how much of your functional threshold power you’ve used and for how long. Your TSS score can be used to determine the intensity of your overall workout and if recovery time is needed in the days that follow.
This metric is included in integrated into Training Peak software, which was developed as a way to further analyze your power-meter data.
While power metrics are more accurate at gauging your pace than a heart rate monitor, most power meters still include heart rate metrics. Why? Because heart rate data explains how your body is reacting to the effort, and how it varies from one day to another. If your heart rate numbers are high but your power numbers are lower than usual, it could indicate overtraining or the need for more recovery between hard workouts.
Often referred to as revolutions per minute (rpm), or the number of times your pedal completes a revolution in one minute, cadence numbers are also included in power metrics and can be used to determine your efficiency. Use this metric, which can vary from person to person, to determine what cadence helps you produce the most power for the duration of your ride.
Power meters aren’t just for cyclists interested in racing; they can be a useful tool for losing weight, too. The kilojoule metric on a power meter provides an accurate way of measuring the calories you burn based on the amount of power you’re producing.
If you’re trying to lose weight, keep track of how many calories you’re consuming on a ride through sports drink and food, then subtract that from the amount of kilojoules you burned on your ride. This will give you an idea of how many calories you can eat post-ride and still stay on track for your weight-loss plan.
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