Monday, January 26, 2009

What is Power?

Let’s start with defining power - In practical terms, power is a combination of how hard and how fast a cyclist pushes on the pedals or how fast an athlete can overcome all the forces holding her back.

Power is simply the amount of work or energy expended in a given time frame and is measured as a watt.

Normally, work or energy is represented as a joule, while time is represented in seconds. So 1 watt is equal to 1 joule of energy per second while 100 watts is equal to 100 joules per second.

As a point of reference, 1 horsepower is equal to 746 watts or 746 joules of energy per second. An elite professional cyclist can hold just over 400 watts for 30 minutes. [I can hold 150W for about 30 minutes before exploding. Good thing I have a day job.]

So - power output on a bicycle is simply a product of how hard you push on the pedals and how fast you pedal. To produce more power, you can either push harder or pedal faster.

On the bicycle, power is also a product of your speed and all of the forces that resist forward motion.

Those forces include wind, gravity, and the junction where rubber literally hits the road. Accordingly, the power an athlete needs for a given speed is dependent upon factors like weight, aerodynamic drag, the road surface, and tires.

Because these factors are different for everyone, when comparing athletes, power is best expressed as a power to weight ratio for climbing or a power to drag ratio for riding on the flats.

Following are approximate ranges for power output to weight ratios at the lactate threshold for men and women of varying ability.

Power Output to Weight (Watts per Kg) at Lactate Threshold

USCF Category 4-5
Women 2.5 to 3.0

Men 3.0 to 3.5

USCF Category 2-3
Women 3.0 to 3.5

Men 4.0 to 4.5

US Domestic Professional
Women 3.5 to 4.0

Men 4.5 to 5.0

Successful Pro Tour Pro
Women 4.0 to 4.5

Men 5.0 to 5.5

At my last test at Boulder Center for Sports Medicine in October, 2008, my power to weight ratio was 2.5. Not very impressive, but at least on the chart! Since that time, with the training we have been doing, and the weight I have lost, I’m probably inching up closer to 2.8.

Next up . . . The Significance of Measuring Power and Energy

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