Bottom line: The effect of "peak power inside the pedal stroke" is measurable and avoidable with proper bike fitting and saddle positioning.
In two different articles regarding power ("What science says of seat angles" & "Intro to training with Power"), Dan refers to the "peak power inside the pedal stroke" as being "the bane of the triathlete during the bike segment." When I first read this I brushed it off as insignificant and not something worth worrying about. As far as I was concerned, a focus on maximizing power in a "SLAM-like" position (by positioning my knee directly over the pedal spindle at 9 o'clock/3 o'clock) has delivered excellent results for me ever since I first got fitted that way back in April 2002.
Then, armed with a PowerTap on each of my identically fitted bikes (one tri, one road), I set about doing some intervals on my CompuTrainer in an attempt to measure & improve power output. The initial results were fine, but more than a little annoying: Despite the fact that the PowerTap Pro was near-perfectly callibrated with my CompuTrainer (measuring distances to within 0.3-5% of each other), the average power measurements during my intervals were measured between 5-10% HIGHER on my PowerTap. How was that possible?? I just chalked it up to some breaking-in period, and hey, what's so bad about producing even more power than I had thought I was previously, anyway?
Fast forward several weeks, when I came across Dan's article on saddle heights (http://www.slowtwitch.com/...tr/saddleheight.html). I decided this was worth some experimentation with my tri bike (what the heck, it's early in the season), and moved the saddle forward about 3cm and up about 5mm to see what the results would be during those same interval sets.
Long story short:
- I definitely felt some intangible benefits of being in a more "open" position
- My average speed improved slightly
- My average and max HR measurements were comparable, if not slightly lower
- My average power output as measured on the CompuTrainer was about the same, and...
- My average power output as measured on the PowerTap was 5-10% LOWER than it had been, and was now roughly callibrated (within 0.5%) with my CompuTrainer.
Basically, I had to conclude that the CT (which measures average power at the tire surface) was much less senstive to the power measured "inside the pedal stroke" than the PowerTap (which has a stress meter integrated with the hub), and that the previously measured 5-10% increase in power with the PT had to be caused by a surge in power that was measured by the PT at 9 o'clock/3 o'clock.
Lesson learned: The power output variance is much lower, and pedaling is much more efficient, if I am riding my tri bike in a "FIST-like" position versus a "SLAM-like" position.
For me, case closed.
In two different articles regarding power ("What science says of seat angles" & "Intro to training with Power"), Dan refers to the "peak power inside the pedal stroke" as being "the bane of the triathlete during the bike segment." When I first read this I brushed it off as insignificant and not something worth worrying about. As far as I was concerned, a focus on maximizing power in a "SLAM-like" position (by positioning my knee directly over the pedal spindle at 9 o'clock/3 o'clock) has delivered excellent results for me ever since I first got fitted that way back in April 2002.
Then, armed with a PowerTap on each of my identically fitted bikes (one tri, one road), I set about doing some intervals on my CompuTrainer in an attempt to measure & improve power output. The initial results were fine, but more than a little annoying: Despite the fact that the PowerTap Pro was near-perfectly callibrated with my CompuTrainer (measuring distances to within 0.3-5% of each other), the average power measurements during my intervals were measured between 5-10% HIGHER on my PowerTap. How was that possible?? I just chalked it up to some breaking-in period, and hey, what's so bad about producing even more power than I had thought I was previously, anyway?
Fast forward several weeks, when I came across Dan's article on saddle heights (http://www.slowtwitch.com/...tr/saddleheight.html). I decided this was worth some experimentation with my tri bike (what the heck, it's early in the season), and moved the saddle forward about 3cm and up about 5mm to see what the results would be during those same interval sets.
Long story short:
- I definitely felt some intangible benefits of being in a more "open" position
- My average speed improved slightly
- My average and max HR measurements were comparable, if not slightly lower
- My average power output as measured on the CompuTrainer was about the same, and...
- My average power output as measured on the PowerTap was 5-10% LOWER than it had been, and was now roughly callibrated (within 0.5%) with my CompuTrainer.
Basically, I had to conclude that the CT (which measures average power at the tire surface) was much less senstive to the power measured "inside the pedal stroke" than the PowerTap (which has a stress meter integrated with the hub), and that the previously measured 5-10% increase in power with the PT had to be caused by a surge in power that was measured by the PT at 9 o'clock/3 o'clock.
Lesson learned: The power output variance is much lower, and pedaling is much more efficient, if I am riding my tri bike in a "FIST-like" position versus a "SLAM-like" position.
For me, case closed.