Power Based Training – Part 1
12 Nov 2005
Some of you might be noticing a steadily increase in the number
of riders using some flavor of a power meter. Like the heart rate
monitor in the mid 90’s, a power-measuring device is becoming more
prevalent due to a myriad of product offerings and accessible
scientific (applicable) research supporting its use. Though the
concept of training by power isn’t new to the research world,
technological advances are pushing it to soon become the basis in
which to train in the real world.
This discussion is the first of three parts. The first discussion is
an introduction to the concept of power and provides the benefits to
train by power. The subsequent discussions will cover power
measuring options and suggestions on how to train by power.
Definition of power
I don’t get many opportunities to leverage my physics degree so I’m
going to take this opportunity to make my college professors proud…
Power is expressed as the rate at which work is performed. This
concept can also be expressed as the amount of work done during a
given amount of time. For those who work 8-5, don’t your hopes up
yet, I’m not talking about that kind of work. “Work” in this sense
is applying a force to an object resulting it to move a certain
distance. The distance piece is critical. Work is only performed
when a force causes movement. Someone does work when he/she lifts a
box or pedals his/her bike. If no movement is caused no work is
done.
So where are we so far? We’ve expressed the concepts of power and
work as:
Power
= Work / Change in Time
Work = Force * Distance
Bringing this concept to rotational systems power is a product of
torque and angular velocity. Torque is defined as an applied force
at a distance from the axis of rotation. Bringing this concept to
cycling, torque is created by applying a force on the pedals at a
distance equal to the crank arm length. For the sake of this
discussion, angular velocity is analogous to revolutions per minute
(RPMs). So for the case of pedaling a bike, power is expressed as
Power = Torque * Angular Velocity
So the rate at which work is performed (power) depends on how large
of a force one applies to the pedals and how fast the pedals are
turned.
So what’s so special about measuring power?
Measuring power provides a more direct method to determine how hard
you work on the bike. Unlike perceived exertion, speed or heart
rate, power is not influenced by variables like weather,
hypohydration, terrain, current stress level, road surface,
altitude, and/or effect of drafting. As a result power not only
better determines how fast one can ride in a head wind or up a
mountain, but also helps give a complete picture of the
cardiovascular, metabolic and perceptual response to do so.
Therefore power is directly related to cycling performance both from
a physics standpoint as well as a physiological standpoint.
Benefits to train with power
There are many reasons to consider training by power. I’ve listed a
few I believe are compelling though there are others.
Have a better idea of your physiological strengths and weaknesses
Measuring power in your training and racing will provide data to
determine what are your physiological strengths and weaknesses.
Power profiling tables (e.g. Andy Coggan’s Power Profiling) exist to
help you compare your current results to get an idea of where you
need improvement.
Train with more focus and motivation
Training effectively takes focus and motivation. Having quantifiable
targets provides an impetus to focus as well as give extra
motivation to work through the pain. For example, while performing a
5-minute time trial effort, you notice the average watts start to
slip at the latter part of the effort you’ll step on the gas to meet
your 5-minute wattage goal.
Tune up your nutrition practices
Measuring power provides how much work (in KJ) you do in your
riding. Knowing how muck work you do is a powerful tool giving you
information to plan your post-exercise nutritional intake (in Kcal)
aiding you to recover faster and properly preparing you for the next
day’s ride.
Make yourself more ‘coachable’
Either if you are self-coached or have a coach, measuring power will
allow ‘the coach’ to see your strengths and weaknesses faster and
clearer. With such data ‘the coach’ can make himself more effective
in helping you achieve your goals.
Make use of training by power and heart rate
Heart rate alone is not a true measurement of intensity but more of
a measurement of the stress to your cardiovascular system. By using
the combination of power and heart rate, you can better analyze how
the cardiovascular system is stressed against a certain amount of
work. Comparing such measurements over time gives you a more
complete picture of how your cardiovascular system is becoming more
conditioned.
Improve you bike position
Though there isn’t a wind tunnel close by, comparing power outputs
in different bike positions can lead to faster times and possibly a
more comfortable position. Power doesn’t lie!
Train more effectively than your competition
What other motivation do you need other than knowing your training
is power based. You can line up at the start line with confidence
because you’re training with such power.
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