Intervals with Power Meter

May 20, 2013 11:05 am

I have been doing intervals on the bike periodically.  I usually a a series of 4 repeats of 7 minutes followed by about a 3.5 minute cool-down.  Before I acquired a power meter it was difficult to see if I was really improving.  With running you can pretty much see your improvement with your pace for each interval, on a bike there are a lot of things that affect your speed besides what you are putting out.  So I picked a relatively flat course that included a couple miles of warm-up from our house and then a straight shot, with no need for stop signs or traffic lights during each of the 7 minute intervals. The blue sections on the map are the intervals done at speed and the red sections the recovery portions.  By using a circular course I tried to average out the affect of wind.

I have data from 15 workouts, the first in March 2008 and the 15th today but this workout was the first one using a Power Meter and it reveals some information I did not realize before.  I have been plotting out my average speed for the intervals, along with my average heart rate and maximum heart rate.  With the new information I have added Normalized Power average for the lap.  Since I only have power for this one workout, I used the Strava estimated power for the past couple of interval workouts so I can kind of see how things are changing.  Since Strava estimates are not that good, once I do more interval workouts with a power meter I can remove those Strava estimates.


When you look at overall averages of all 4 intervals, there is a relatively good correlation between speed and heart rate, except in the period 2010-2011 when I was on a beta blocker.  Power also seems to somewhat follow the same pattern.  What I did learn, however, was that there much less correlation between the individual intervals of a workout.  Typically the 4th segment is done at the fastest speed, but that has more to do with the prevailing winds and topography than with my actual effort.  Today for that 4th interval segment I averaged my best speed of 22 mph, but my normalized power dropped from 219 watts for the first interval to only 142 watts.

I also learned that I can not put out the same type of power level when I am riding flat compared with climbing, even though my heart rate is high.  When I am with a fast group on the flats I have a hard time keeping  up until we hit the hill where I can go ahead.  I just thought that was because I was a light weight guy, but now I realize that I am not generating as many watts while riding flat, for the same perceived effort, as when climbing.  Last week I was able to average 235 watts for 20 minutes while climbing Henry Coe.  But today my best interval of 7 minutes was only 219 watts and the rest of the intervals were below 200 watts.  This is not a matter of aerodynamics because I am looking a power, not just speed.  It has to do with my riding style and not putting as much power to the pedal on the flats as I do while climbing, where I often stand a lot.

It is clear that training with a Power Meter is a great aid and it has helped me to see some things I did not realize before when I was just looking at speed and heart rate.

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