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Training with a
Powertap Hub |
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A Powertap hub replaces the rear hub on your road bike.
Inside the hub, there's a strain gauge that measures how much torque
you're putting into the spokes. A magnet determines wheel RPM (just like a
standard bicycle speedometer). From torque and RPM, the computer
calculates how many watts of power you're delivering.
The unit comes with a heart rate monitor. Knowing both heart rate and
power output lets you train more efficiently and monitor your progress
with real numbers. |
| There's also an attachment for your crank that measures your
pedaling cadence. This lets you find the gearing and the pedaling speed
that gives you the best sustained power output.
You may also learn how seat position and handlebar position affect your
ability to deliver power to the pedals. For example, even without
considering wind resistance (testing on a trainer inside), I can deliver
10 to 20 watts more average power at the same heart rate and
exertion level if I'm down in the drops of the road bike, rather than on
the hoods. |
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The display unit is like an oversized bicycle computer. You
can set up the display to meet the needs of your current workout or test.
After the workout, you can download the data to your computer for
analysis.
A Powertap is expensive. The best strategy is to find a roadie who has
one, and who will let you test yourself on his/your trainer. Once you've
established your heart rate training zones with a baseline GXT and Power
Profile, you create your workout plan. Then you go back to re-test
yourself once a month as you prepare for the racing season. |
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Graded Exercise Test
The Graded Exercise Test (GXT) measures cardiovascular fitness. It
shows your body's response to increasing workload. It can also identify
lactate threshold wattage and heart rate. Each minute, you push 20 more
watts, while recording heart rate, perceived exertion level, and
ventilation comfort.
At right is the raw data as recorded during a GXT session. Below is the
plotted data.
The GXT can be used monthly to show improving cardiovascular fitness,
higher lactate threshold, and higher steady-state power output.
GXT Data Sheet
GXT Graph Sheet |
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| A plot of heart rate versus power shows the
cardiovascular response to increasing workload. The lactate threshold
heart rate is about 10-15% below the point where breathing becomes labored
(perceived exertion about 7/10). Heart rate training zones (and wattage
training zones) can be calculated for recovery, endurance, lactate
threshold, and anaerobic power. |
The GXT can follow both cardiovascular
fitness and power delivery. This graph shows a hypothetical second test
one month later. The line has shifted down and to the right. Each power
step is achieved at a lower heart rate. Lactate threshold is reached at a
higher wattage, meaning you can ride faster in a long race. The peak power
achieved has also increased. This shows improved fitness. |
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Power Profile
Power Profile testing shows what you're capable of. If you're always
bailing off your bike on those very short but very steep climbs, you need
to improve your 12-second (0.2) power. For a rolling course like Five Mile
Pass, you're looking for improvement in your 1-minute power. For ride
that's mostly flat (for example, the ULCER) you look for improvement in
the 12- and 30-minute power.
In addition to monitoring improvement, the Power Profile lets you match
power output to the course, so you don't "blow up." From the
graph at right, you could predict that for a 3-minute hillclimb, the rider
could maintain about 350 watts average power.
Power Profile Data Sheet
Power Profile Graph Sheet |
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Time Trials
You can run a time trial based on either a fixed distance (for example
3 miles), or a set time (example 20 minutes). The test should be done
while rested (during a recovery week), under similar conditions -- same
course, same time of day, same wind and temperature conditions, etc.
You're looking for higher average speed and higher average power.
Time Trial Data Sheet |
| Training with the Powertap |
Every rider is different. The key to improving is to match
your workouts to your own recovery ability, anaerobic strength, and
aerobic fitness. It's not a simple thing to do that. A heart rate monitor
is the most important addition to your standard bicycle speedometer. The
Powertap adds another layer of science to your workout plan.
If you're rich enough and motivated enough to buy a Powertap, you can use
it to improve the efficiency of your workouts. For example, if you're
trying to increase your power at Lactate Threshold (which is your primary
goal for cross-country racing), the computer lets you stay in the power
zone and heart rate zone that will give you the biggest bump.
If your goal is power improvement, you can fine-tune the wattage to get
the maximum growth stimulus to your muscles while minimizing muscle
damage. Hit the muscles, but minimize the amount of time you'll need for
recovery before the next workout.
And what about the day when your heart rate is way up there, and you feel
you're working really hard, yet the hub shows pathetic power delivery
compared to previous training sessions? Well, it's telling you to abort
the training session, because your recovery isn't complete from the last
one. There's nothing to gain from continuing.
To use a Powertap to match interval training to your current fitness
level, go to the Anaerobic Interval Training
page. |
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