Power Meter

power_tapSo, I recently got a powertap hub made by CycleOps.  It’s a pricey gadget, but the value proposition is extremely compelling.  This baby replaces your rear wheel hub, and emits wireless signals (via ant+) to a head-unit that gives you all sorts of readings.

You see a lot of post-race analysis focusing on power.  For example here is a nice post-Kona debrief over at slowtwitch (mckenzie, jacobs and al-sultan).  And here is a cool youtube where Andy Potts talks about his usage of power in training.

Being the curious enthusiast, that was enough for me to explore the concept of training with power.

I’ve logged quite a few miles with the powertap in the last month or so.  But have only casually noticed the readouts.  I think just seeing your readout is pretty helpful.  That feeling of slowing down, whilst seeing your watts go up and altitude increase gives you peace of mind.

But now it’s time I actually start putting this tool to proper use.  After going through Joe Friel’s, The Power Meter Handbook, I’m starting to realize how a triathlete can take a pretty measured approach in training for the cycling leg, with specific performance targets in mind.  And it has nothing to do with being a pro.  The level of investment required aside, I think it makes more since for a complete novice to train with power than it does for a pro.  Speaking from experience, it’s most helpful for a beginner (e.g. me) to have very specific measurable goals they can track progress against.  In fact, all the other methods like training with RPE or Heart Rate seem like complete freak’n hogwash now.  I can see HR continuing to be an important metric, but only as it relates to power.

So how do you train with power?

Functional Threshold Power (FTP)

You hear a lot of riders that use power talk about this FTP thing.  FTP basically indicates how much power  you can generate based on your current fitness level, for an hour.  So, in the world of power based training (and racing),  the goal is to have an FTP that matches up with your target performance.  All objectives are built around this FTP number.

A real-life example

For a bit of fun, I’ll try to document my real-life experience as I begin training with power.  I’ve signed up for the HITS Napa Olympic Distance race on April 14.  So I’ll establish some goals and then chart my progress.

The bike leg is about 25 miles.  I want to achieve at least a 20 mph bike split, or a ride time of about 01:15:00 or better.  This is a couple of miles per hour faster than my last oly-distance bike split, so it’s a good next milestone.  And honestly, I have no idea how I’d train for this objective without power.  I’d be feeling my way, doing a bunch of RPE level 7s and 8s, or doing many workouts with my heart rate pegged near lactate threshold (which itself is somewhat of a guess).  And all that may very well work (at least I’d hope).  It just seems kind of silly in retrospect.

Anyway … so the first thing I must do is identify my current FTP.  There are a number of ways to determine your FTP, but I’ll start out by using the Friel method.

friel_method_ftp_trainerroad

The Friel method for identifying FTP is by basically riding all out for 30 minutes.   But 30 minutes, not an hour you say?  He explains the logic in the book; check it out if you’re that curious.  Anyway – these are brutal tests! I’m not looking forward to periodic check-ups!  That long flat-top looking bit in the chart is my power output for that 30 minute span (15 min warm-up, 30 min test, 15 min cool down).  So, using the CycleOps Power Agent software, I’ve identified my FTP for that 30 minute window to be about 207 watts.  The chart above is from Trainer Road, and is using virtual power.  The powertap recorded readings a little lower, which I’ll use since its mounted on my bike.  Coincidentally, I had a brief “give-out” moment where I decided to try and let my heart rate come down.  Very visible right at about minute 35 on the chart above.  Notice how much my power dropped, while my heart rate only dripped negligibly from 174bpm-ish to 169bpm maybe.  With a power output decrease from 212 watts to 170 watts.  Case in point.

So I have my FTP, now what?

Now I can figure out how much power I need specifically for the HITS Napa course.  And I can do this using this handy calculator, courtesy  CycleOps.  But first to make sure I’m level set on my calcs.  I can check accuracy with the pro information from slowtwitch.

pro-power-output

Both Luke and Pete are about 70 inches tall and weigh around 150lbs.  The CycleOps watt calculator is pretty darn close (272 vs. 281 for Pete, and 264 vs. 265 for Luke).  It’s hard to peg Faris’ figures because distance nor mph are included … and it’s only 20 minutes worth of data.  It’s unbelievable these guys can push that wattage for that period of time … that’s near 25mph average for 112 miles!  Straight ballistic.

Rubber hitting the road

So now I have have some pretty valuable information.  After plugging in my vitals with HITS Napa specific info, it looks like I need to achieve an average of 204 watts to reach my objective for the bike leg.   And I’ll be able to use this same technique later for Vineman 70.3.  The calculator ignores unpredictable metrics like wind, having to slow down for other racers in the way, or slowing down for turn-arounds etc.  Oh yeah … I’ll also need energy to run after I get done on the bike (obviously).  So I need to plan to ride at about 75-85% of FTP intensity.

I can see right away that I have a ways to go, training wise.  Riding at 80% of my current FTP leaves me with only 165 watts of pedal power.  I need to increase my ability to work and decrease weight to make up for about 40-50 watts (204 watts / 80% = 255 watt FTP).  Sounds trivial  but remember, my FTP of 207 watts was ALL OUT.  Increasing 40-50 watts from here seems kind of daunting, actually.

Increasing FTP

Referring back to Joe’s book, a rider increases FTP by riding near or slightly above FTP levels (95% to 105%), but mainly around 90%.  And that seems logical, our bodies get stronger through adaptation.   Also, since weight is an input, losing weight increases FTP as well.

So I have my marching orders.  Get FTP to 250+.  This feels like a good next-step target.  Because I’m sure to to achieve similar results at twice the distance at Vineman 70.3, my IF will need to come down, which means my FTP will need to go up even more.  What fun.

It’s kind of refreshing to have such a simply stated metrics to measure against.

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One thought on “Power Meter

  1. Ran the calculator for the numbers Andy quoted in the youtube. He’s 75 inches tall (6′ 3″) and 175 lbs (per Wikipedia). For Oceanside, CycleOps watt calculator says 333 watts vs. the figure he quoted in the video of 358 watts. Hard to know if that 25 watt delta is equipment specific or not. The 330 watt metric matches what he says he does “every day.”

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