# Running with Power: How it Works and What it Means

Monday, December 5, 2016 | By Guido Vroemen

Using power to train and race has been widely used in cycling for more than a decade, but recently running power is the new “it metric.” It can be stated that the power P of our human engine should be equal to the sum of the power required to overcome the running resistance Pr the air-resistance Pa and the climbing resistance Pc as shown in the figure below.

Figure: The Running Model

Recently, the first power meters for running were developed. This means that you now have the possibility to measure your running power in real-time. Using this data you can start to optimize your daily training and your race performance. This also makes is possible to quantitatively determine your “running economy,” which will allow you to fine-tune the amount of energy you are using at various intensities. By optimizing your running economy you will learn to change your running form and evaluate more precisely the impact on the energy cost of your running both in training and while racing.

## The Experiences in Cycling With Power

Power meters are well-known in the cycling world as a valuable tool. The widespread use of power meters helps amateurs and professionals alike optimize their training and their race performance.

In cycling, the measuring principle of the power meter is based on strain gauges to determine the force F, delivered to the crank shaft. This force multiplied by the speed v, results in the power output P = F*v.

Both in theory and in practice, a very strong relationship is found between the power output and cycling performance. In the book “The Secret of Cycling,” my colleagues and I found that on a flat course the performance is determined by the total power output P in watt. Contrary, in the mountains the performance is determined by the specific power SP in watt/kg.

The use of power meters in training and in races offers many advantages. With a power meter you can measure your effort exactly, so you can optimize your workout and find the right pace in a race. Without a power meter you have to rely on your speed or your heart rate (HR). However these strongly depend on the conditions. Facing a headwind or cycling uphill your speed is much less while pushing the same wattage. At the same speed your HR is higher. Your HR is also related to the temperature and your overall physical fitness.

## The Breakthrough of Power Meters in Running

Because of the proven value of power meters in cycling, the search for a power meter in running has been going on for years. Obviously, it is difficult—if not impossible—to directly measure the power provided by the legs of a runner. Consequently, another measuring principle has been developed. The breakthrough came with the use of accelerometers. These are small chips containing crystals that exhibit a piezoelectric effect during an acceleration. This piezoelectric effect produces a voltage, which can be measured. Accelerometers are now very cheap, very accurate and have already been applied in many devices such as smartphones, tablets, cars, pedometers and running watches. As a result of accelerometers your smartphone knows if you hold it horizontally or vertically. Accelerometers in your running watch are able to measure your vertical oscillation, cadence and stride length.

## The Stryd: a Revolution in Running?

Very recently, a practical running power meter has been developed by Stryd in Boulder, Colo. Early in 2016 the Stryd Pioneer became available to the general public. The Stryd Pioneer meter is a simple pod supplied with a chest band, which also measures your heart rate. The sensor includes three accelerometers. These measure the acceleration of your body in three directions: horizontally, vertically and laterally (sideways). Obviously, it is important to restrict the vertical and lateral movements to optimize your running economy. With their app you can program your body weight. During training or racing you can see the real-time data of your running power (in watts) on your running watch or smart phone. After the training or race, you can analyze all the data on your computer.

The power P is calculated from your body weight m in kilograms, the acceleration a (m/s2) and the speed v (in m/s) using the formula:

P = F*v

F = m*a

The breakthrough of Stryd is obviously their software, which allows the real-time calculation of the running power from all the 3D-acceleration data. The basic formulas are simple, but it requires a complex algorithm to integrate the accelerations in all directions in a correct and stable manner. One of the advantages of the Stryd is that it provides you with accurate and real-time information on the power that you are producing in your workout. This gives a much better representation of your real effort than your pace or your HR alone.

## The Potential Benefits

Power meters may provide a historical and revolutionary breakthrough in running. The use of accelerometers combined with advanced software seems to have paved the way for runners to get realistic and reliable data on their running power. Many potential benefits have already been identified, but here are some of the most promising ones:

A power meter will tell you (each and every day!) how much power you are using and thus how economically you are running. By changing your running form (e.g. cadence, stride length, etc.) you can measure whether or not your running economy improves.

### Measure your fitness and shape.

You can now measure your FTP and your VO2max, without the need to have yourself tested in a sports medical center. This means you can now determine how your fitness evolves.

### Measure the exact effort of your workout.

A power meter provides realistic and reliable information, better than pace and HR. This means you can prevent overtraining, adjust your training and optimize your tapering.

### Maintain the optimal pace in a race.

Obviously, changing conditions, such as wind and hills, will affect your pace. Power data will help you to maintain a constant effort, so you do not blow yourself up or have something left in the tank at the finish.

### Optimize communication with your coach.

Daily exchange of the data on your workout (power, HR, pace, running economy, etc.) will be of great value to your coach so he can make a more precise training plan for you.

Obviously, the application of running power meters is still in its infancy. In practice, these potential advantages still have to be proven over time. It is possible that other advantages to these devices will materialize in the coming years as the quest to optimize running performance continues.

Thank you to co-authors Hans van Dijk and Ron van Megen for their contribution to this article.