After my last post it was brought to my attention that training and racing with power is a comprehensive topic. While some athletes have a good understanding and grasp of what power is, the majority lack a clear understand of the fundamentals and principals of how to train and race with power. I plan on doing several posts beginning with the basic principals before moving to more advanced topics. Power 101 here we go.....

What is power? The Inside Working of a Power Tap HubPower is defined as the rate at which work is performed per unit of time.Power = Work/Time Work is the result of taking an object and moving it a particular distance with a defined force. Work = Force X Distance If you substitute this into the first equation the result is Power = Force X Distance / Time Distance divided by time can be expressed as Velocity (or speed). Therefore the equation for power can also be expressed as:

Power = Force X Velocity

How is power expressed on a bicycle?
When a cyclist is rotating the pedals of a bike, Force is one component of theTorque (a form of Work) the rider applies to the cranks and the cyclists cadence (RPM’s) is measured per unit time. Therefore:

Power = Torque X RPM

If a cyclist wants to produce more power they must either push the pedals harder or pedal faster.

How is power expressed as energy?
Power is directly related to energy expenditure and is typically expressed in Watts1 Watt = 1 joule of energy per second (a joule being a measure of work). In cycling you will often hear reference to the number of watts a given athlete was able to produce over a give period of time (average watts).

How do Power Meters Work?
Hub and crank based power meters are currently the most common, however there are two companies that will be introducing pedal based power meters sometime this year. All of these systems use mechanical devices called strain gauges.  A strain gauge is fastened to an object and when it is deformed the electrical resistance changes. This change in resistance is measured and converted toTorque and Cadence allowing a cycling computer to accurately measure Power.

Written by Kyle Visin
Santa Barbara Triathlon Club Co-President
USAT Level 1 Coach
Certified CycleOps Power Coach
Co-Founder of KillerTri

A duplicate post is also available at www.killertri.com