If you spend any amount of time reading any literature dedicated to cycling and triathlon, you will surely have noticed the volume of writing committed to the Power and related topics.

Power in cycling has become the Gold standard tool used by many athletes to represent their training intensity.

It has allowed us to take the Science of sport, to the next level.

Q: What exactly Power is.

Simply put, it is the rate of performing work, and is the product of Force and Velocity, and is presented in watts (w).

Power (w) = Work/Time

Translated into bike talk, it is the amount of time it takes to do a certain amount of work. Perhaps complete a century race, or a 40km time trial.

Asker Jeukenderup says it best: Power is the amount of energy that is transferred into the pedals every second.

Unfortunately, we are not very efficient on the bicycle, and this reading represents about 20%-25% of the total energy produced. This means the other 80% does not result in power transfer to the pedal, but is lost as heat energy.

So we now have a better understanding of what it is, how about looking a few numbers that give us some perspective on the sort of power outputs that are generated during various cycling efforts:

Obviously the more conditioned the individual, the better able they are to sustain a greater Power output for an extended period of time.

Q: How do we measure Power?

Most cycling power meters make use of a strain gauge to measure the torque applied (the strain gauge strip are attached to the crank and measure the "stretch" of the strip when a force is applied to pedal), and, combined with angular velocity (Pedalling speed), we are able to calculate power.

These strain gauges are mounted in the bottom bracket, rear hub or the crankset of the bike.

There are newer meters that do not use strain gauges, but instead measure power through a handlebar-mounted unit that measures the forces opposing the cyclist (gravity, wind resistance, inertia, rolling resistance) and combining these with velocity to determine the rider's power output.

It is based on Newtons 3rd Law: For every action, there is an equal and opposite reaction.

Q: What is the benefit of using Power to gauge intensity over other methods (Heart rate for example)?

Power is the bottom line when it comes to bicycle racing.

It is far easier to determine at what Power output you must ride to complete a 40km TT in a Personal Best time, compared to using Heart rate.

There are many external and internal factors that affects Heart rate: External factors such as Environmental conditions such as: Heat, Cold and humidity, Physiological factors: Cardiac Drift, Dehydration and Fatigue or Other factors, such as: Caffeine, Medication and lack sleep.

Power is affected by anything that impacts your bodies to function efficiently (Increase in workload), however, it is shown in a real time display.

When the workload increases, the Power increases immediately - no delay - unlike heart rate, which takes a period of time to respond the increase in demand placed on the body.

Q: Why don't we all then use Power?

The most obvious answer is cost.

Power meters are not cheap, and not affordable to all cyclists. As a tool for maximizing your performance, it can prove to invaluable, and at the higher levels of competition, can be the difference between winning and losing.

Another factor is actually taking the enormous amount of information you can acquire from your Power meter, deciphering it and then applying it to your program.

At the end of the day, whatever you decide to use to quantify your training intensity, the most important thing is that you are able to clearly differentiate between different training intensities and what energy system is being used .

James Greenwood is a competitive tri and multisport athlete currently training for Ironman Canada 2009. A level 1 Triathlon Coach, he holds a post graduate degree in Exercise Science, and is a Certified Strength and Conditioning Specialist through the NSCA. James is also currently the resident health and fitness programs expert at MyPypeline.com, and has starred in a number of multisport specific fitness videos.
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