Six Ascents of Old La Honda: Time vs Weight

2014-08-03 • SEND FEEDBACK •
Related: bicycle power meter, glycogen, SRM, training

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This workout analyzes six ascents (“repeats”) of Old La Honda Road for time versus weight (fluid loss), and power meter consistency precision).

I went into this workout not fully recovered from a demanding week of prior training, so I didn’t know how it would go. Curiously, I began to feel stronger by the 3rd ascent even though my quadriceps had that sullen “dead” feeling on each ascent. But as they “opened up”, the power improved. It’s a curious thing, but a behavior I’ve seen before on long rides.

Accounting for fluid loss

With warm temperatures, a lot of fluid is lost: total riding weight was 201.3 pounds at start to 197.8 pounds when done, with 2 liters (4.4 pounds) of water and 0.4 pounds of Hammer gel consumed, e.g., 8.3 pounds were lost in total over the 3 hour 23 minute effort.

Most of that weight differential is water, and more than it seems: muscle use of glycogen as fuel releases quite a bit of water. It is one reason that full muscle glycogen stores can delay dehydration of calculated fluid needs.

I calculated a total riding weight (bike + rider) for each ascent based on the starting and ending body weight on a highly accurate and highly precise scale.

Analysis

The SRM DuraAce 9000 power meter is highly accurate and perhaps even more important, highly precise, using the scientific definitions for both.

Temperatures: 71°, 71°, 75°, 77°, 77°, 77° F

The 6-ascent workout is shown below. Discussion follows.

Click for a larger graph. Red is heart rate, green is power.

Six ascents of Old La Honda Road (2014-08-03)

Negative splits

Negative splits (decreasing times) are a good thing to aim for with a repeat workout, so long as the spread is not too great (e.g., the some splits were too slow).

That the splits are negative is self evident from the increasing wattage (they are harder efforts on the same fixed course), but what would ascent times have been with no change in weight?

Shown below are actual ascent times (red), ascent times adjusted for weight (orange), relative weight (green), wattage (blue).

Analysis of 6 ascents of Old La Honda Road (2014-08-03)

Power meter consistency (precision)

What would the times have been for constant weight and constant watts?

In other words, a power meter that is consistent (precise) should show the same times when the difference in wattage and weight is factored in.

Here, the starting and ending weights were taken ~10 minutes before the first ascent and ~18 minutes after completion of the last ascent (final weight adjusted upwards slightly to account for that 18 minutes).

The actual weight for any particular varied by temperature and by fluid consumed prior to that ascent; I didn’t carry a scale along! So there is going to be some error on weight for intermediate ascents.

Here are the relative power readings adjusting for constant time and power. A figure of 1.01 means a variance of 1%. The largest variance is 1.1%, but laps 3/4/5 show a variance of only 0.3%. Given the weigh estimates, it‘s fair to say that the SRM is highly accurate and precise. That’s a crucial gauge of a power meter. Years of riding on various fixed routes support that statement.

1.000 1.011 1.004 1.003 1.003 1.008