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Understanding Power and Power Meters

Since first introduced in the late 1980s, power meters have revolutionized cycling, changing the way we train, race, and even recover on the bike. While power meters were originally an exclusive training tool for professional cyclists, it's now common for cyclists of all levels to train with power. However, understanding power and how to utilize data collected from your power meter can be overwhelming for any cyclists, new or experienced. With a fundamental understanding of power, riders can apply the benefits of power meters to help accelerate their cycling performance. 

What is Power?

In cycling, measuring power provides an objective calculation of the actual work you’re performing when pedaling. We use watts as the unit of measure when talking about power and in its simplest form, power can be described as:

Power = Torque x Cadence

In this equation, torque characterizes the amount of force or effort a rider generates on the pedals, while cadence is measured in crank revolution per minute. Together, this equation means that if you pedal harder at the same cadence or if you pedal faster at the same torque, your power will increase.

Measuring Power

Power is measured in a variety of ways on the bike. One of the most common and widely accepted methods is with a power meter crankset, such as the Shimano DURA-ACE Power Meter. Strain gauges embedded in the crankset measure tiny amounts of deflection or bending in the crank that occurs due to pedaling forces. These microscopic movements are used to continually calculate your power, which is then transmitted via ANT+ or BLE signal to your handlebar-mounted computer or smartphone app. These devices collect and store the data transmitted from your power meter, enabling real-time power monitoring during your ride or post-ride analysis by you or your coach. 

Shimano's DURA-ACE Power Meter uses Bluetooth/ANT+ technology to pair to your cycling computer giving you live power data.

Training with Power

Training with a power meter is especially useful in cycling because this measurement provides a clear view of how hard you are working. Other metrics such as heart rate are more subjective and can vary on a day to day basis depending on external factors such as caffeine intake, sleep quality, and hydration. While heart rate training can provide helpful insights into the cyclist's performance and effort, it does not offer the same objective view as power.

Along with heart rate, measuring your speed and average pace provides some insights into your riding performance and effort, but these metrics are not as clear-cut as power. For instance, if you usually complete a local training route with an average speed of 18 mph, but today you only managed 17 mph, you might think that you had a poor performance. However, windy conditions could have affected your pace, slowing your down despite pedaling harder than usual.

If we add a power meter into the mix, you might find that your power was actually 20% higher on the windy day. Even though your average speed was slower than usual, your power meter revealed the truth that you had a great workout. Many factors beyond wind can affect your average speed, including hills, drafting in a group, and tire rolling resistance. While speed offers some useful information about training, it does not provide a complete picture.

FTP and Training Zones

Training or racing with power can also help guide cyclists in their effort levels during workouts or in races. Knowing how hard your body can push for specific amounts of time can help you meter your efforts so that you have enough energy left at the end to strike your attack or to finish your workout without falling apart.

Many cyclists utilize training zones, or power zones, to distinguish different effort levels. A common practice to establish these zones is first to determine your functional threshold power, or FTP. Your FTP represents the maximum average power you can sustain for a full hour of all-out cycling. Fortunately, instead of doing an hour-long test, you can perform a 20-minute maximum sustained effort while measuring wattage. Then multiply that average by 0.95 to determine your approximate FTP. Your FTP number can then be used to establish training zones, which are used to create your day-to-day training schedule. 

Riders with a solid understanding of what power measures and how it's calculated can better utilize power in training to ride smarter, race faster, or learn when to pull back and recover better. Power meters are an easy and reliable way for you to plan your training and measure your progress over time to ensure you’re on track to reaching your goals.  

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