Why train with power?

Friday, March 1, 2013 by Coach Tommy

Why train with a power meter on the bike?  I get asked that often.  The simple answer is that the power meter is a more precise and accurate tool for gauging cycling intensity.  Power is a better indicator of intensity than heart rate, speed or rating of perceived exertion (RPE). 

Power is the measure of the output of your body working on the bike. 

Why not heart rate? We’ve been using heart rate for monitoring training intensity since the late ‘70s.  Why not continue using heart rate?  It has worked fine for decades.   Well, we have newer technology that works better – power meters. To delve a bit deeper into why power, I’ll use an analogy – the race car and the human body.  The race car has an engine (muscles) and within the race car there is also a fuel pump (heart).  As the engine (muscles) works harder in order to perform at a higher speed (or intensity) the fuel pump (heart) reacts and works harder to deliver more fuel (oxygen and nutrients) to the engine (muscles). 

Notice that the heart is reactive.  It reacts to the demands of the muscles.  Your brain says ‘Go faster’.  Your muscles ramp up their work load and demand more oxygen and nutrients.  Your heart reacts and beats faster delivering more oxygen and nutrients to the working muscles.  Using heart rate to gauge intensity is like watching the fuel gauge in the race car in order to determine how hard the engine is working.  The fuel gauge (and heart rate) is good information.  But that’s not a very efficient way to figure out how hard the engine is working.

Heart rate is an input into the production of energy.  Power is the output or the result of the production of energy.  Measuring the output is much more valuable and a more direct measure of intensity than measuring the input or heart rate.

Even so, heart rate is still valuable information.  I use heart rate and power combined when evaluating my athletes’ training sessions and races.  So, don’t throw away your heart rate monitor.

Why not speed? Speed is the worst gauge of training session intensity.  Speed on the bike is dependent on environmental conditions like wind and on the terrain – hills.  A training session on a hilly course and a flat course could have the same energy usage and power output, but the hilly course workout will be slower than the flat course workout. 

However, there are athletes for whom I will say “Go out and ride at this speed for this long”.  This is more of a mental training exercise than a true physical training session. 

Why not rating of perceived exertion or ‘feel’? Rating of perceived exertion (RPE) is a measure of your feeling or perception of how hard the training session or race is.  RPE is usually measured on a 1 to 10 scale with 1 being very easy and 10 being very hard.   RPE is useful but the athlete needs to be very experienced in using RPE.  The risk with RPE is making the wrong judgment and going too hard for too long then having nothing left for the run. There is an “art” to using RPE.  I’ll ask my athletes “How did that ride feel?”  I’m judging their perception of the ride intensity with what the data tells me.  If there is a discrepancy, then we have a discussion about how that ride should ‘feel’.  I’m calibrating their RPE with what the data tells me.

The power meter has become the gold standard for measuring intensity on the bike.  Heart rate, speed and RPE have their place in a training program, but the ultimate measure of training intensity on the bike is power.

I will go into more detail about power in subsequent posts. 


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