Why train with a power meter?

In the interest of full disclosure I will note I only have a power meter on my trainer.  It is very expensive and/or inconvenient to have an on board power meter.  This is soon to change.  The company I am waiting for is Brim Brothers who will place the power meter in the cleat of your shoe.  This will be bike independent.  They seem to be the most honest in terms of projecting their delivery date.  Assuming they are reasonable on their price, my money will soon follow.

Now to the point, why train with a power meter?  The easiest place to start with this question is actually running. If I run up a hill one day and on a flat surface another day, these are two very different workouts.  Trainingpeaks refers to this as Normalized Graded Pace and is expected to be available on their web interface (as opposed to their WKO+ software).  Now you might conclude off the cuff, that this is not too much difference.  But at the end of the day, for a triathlete.  In particular we are not simply swimmers or bikers or runners, but a hybrid of the 3.  Lots of little differences add up to big issues.  Are you training hard enough?  Are you training too hard?

At the end of the day we are looking to push our cumulative training load up to the edge and a little past, then back off.  For biking we can use power output.  For running NGP, which uses GPS data to determine workoad.  Ideally for running we could capture wind resistance too, which would give us close to power output.  But with a power meter on the bike and GPS on the run we get pretty darn close to your work effort each workout and the cumulative build up over time.

Now some folks who race faster than me and might even be smarter argue only for heart rate training.  But in the same vein as above many things change heart rate.  The  biggest  immediate factors are diet 24 hours before, temperature the day of and sleep.  So you could finish a workout and say wow I did great, my heart rate was X.  But reality is that you did very little work because your heart rate was elevated from cookies last night and 6 hours of sleep with 80 degrees and humid conditions.

This is not to dismiss heart rate.  It is actually extremely important, but it is one of only several important aspects of determining proper training load.  Thinking of triangulating cell phone positions we need three data points.  For training it makes the most sense to have power, heart rate and perceived exertion.  If we can replace perceived exertion with something less arbitrary we will reach the holy grail.  It might look like power, heart rate and some factor taking into account air temperature, blood pressure, wind resistance and breath rate.  This would require science a bit a past where we are today but is well within reach.

Happy Training!