Power vs speed vs cadence test? Analytical types needed...
I know this has been discussed so many times but I am trying to find some way to measure the effectiveness of different cadences. It is too hard to hold enough variables constant outside so I am trying to do a test on the trainer. I rode three 8 minute intervals at different cadences, holding power constant. The variable to solve for, of course, is speed. I assume that since the resistance on the trainer is constant, then speed should be able to be determined. (The fourth x-factor is the "exertion" required at the different cadences, but that seems to be a very individual thing.)
Here are my interval test results:
Interval #1: NP=252(VI=1), Avg Cadence=82rpm, Avg Speed=22.9mph
Interval #2: NP=251(VI=1), Avg Cadence=80rpm, Avg Speed=23.9mph
Interval #3: NP=249(VI=1), Avg Cadence=85rpm, Avg Speed=24.1mph
Why can't I get good data to draw a conclusion about optimal cadence? Is there something wrong with PT? Basic conclusion is that I should ride at the higher cadence?
Thanks for anyone has gotten this far on this super long post, and taken the time to respond!
Comments
I think perhaps what you are trying to determine is what cadence gives you the highest watts at the lowest perceived effort? That might be a lot harder to figure out from a data point of view, but I think that the new Quadrant Analysis capability of WKO 3.0 might help us all get there. I need to read (and think) more about all of this. My gut tells me that in the end- we all have a cadence that works for us individually and our Quadrants will all look essentially the same with just a different # in the center. But again, I haven't done much reading or playing with this new tool yet. Here's a link to the trainingpeaks site where they discuss the tool a bit more: http://home.trainingpeaks.com/articles/cycling/quadrant-analysis.aspx
John, like Nemo said plus:
If you are spinning at a higher cadence the force you apply to the pedal is less but done more times/min to do the same work. You might consider using either your RPE (rating of perceived exertion) or average heart rate for the interval as approximations of the effort at different cadences.
Do you have avg HRs for the 3- 8 min intervals?
John
I use a CompuTrainer, not a PowerTap + Trainer, so what I observe does not apply to your question, but it presents its own puzzle as to "what were they thinking" when they designed the algorithm. I just went to my power penthouse (aka pain cave) and I set the computrainer to hold resistence at a constant level, say 120 watts. When I vary my cadence, the "speed" reported is directly related to the cadence. E.g., cadence of 60=16 mph, 80=20 mph, nad 90=22 mph. Funny thing, is, speed does NOT vary with watts. No matter how high or how low I set the watts, the speed is the same at any given cadence.
As I understand it, John, your question is "Using my indoor trainer and power meter, (how) can I determine the most efficient cadence, i.e., getting the fastest speed for a given constant power output?"
Since the power reading in your set up (unlike mine) will always represent some degree of variability, maybe you just don't have enough data points? Maybe you need to do 3-D plotting, instead of just assuming the power is constant?
I'm in the school that says, the fewer rpms you're using, the harder your muscles are working (the more fibers needed) with each pedal stroke, and thus you should strive for the fastest cadence you can manage to hold for the length of your race, to rest as many fibers as much of the time as possible.
I think the best way to answer the cadence vs power output is with a computrainer set in erg mode at your FTP. In erg mode, the computrainer matches the pressure at the back wheel to force you to exert a certain amount of watts, i.e. if you try to pedal faster it will loosen the pressure to generate the same watts output. If you slow cadence then pressure goes up (forcing you to generate more power on each stroke to generate the same power product). After a good interval, say 20 minutes or so my cadence seems to drift naturally to the point where it is easiest for me to maintain the power output, in general around 90 for me.
Your 4th x-factor, ie, RPE, is the all-important component that's missing. Although optimal cadence is trainable to a certain degree, it is my opinion that the appropriate cadence for you will always produce the lowest RPE.
So, you can certainly do a test using erg mode on your CT, as Kevin suggested. However, it will also become completely evident where your optimal cadence lies by simply just riding. You will naturally select a cadence that feels most comfortable. If that's around 75rpms then so be it. If it's around 95rpms then that's fine too.
Although I hate the term, I believe this is one of those areas where people often over think the issue. I focus on two basic goals that align with each training period:
1. During a general prep period I will train at a wide range of cadences to ensure I have some comfort level across the spectrum (while still focusing much of your time around your natural/self-select cadence).
2. During a race-specific prep period I focus most of my time on riding at my natural/self-select cadence using proper gearing for the type of terrain I will experience in my A race.
Thanks, Chris
Can make an argument that thinking about cadence at all is over thinking it. I know that we can get caught up in all kinds of minutae around here and an argument can be made that most of it is just that but cadence is one thing always on the who cares list for me.
Seems to work itself out. Kinda like running form or running cadence.
Maybe that over simplifies but as Chris mentioned RPE is a huge consideration. For me if I am goint to ride at FTP on the trainer I know there is only one, maybe 2 gears I can hold it for any length of time. Outside tends to be true with changes for terrain and wind. Would I ulitmately be faster if I forced myself to ride at a cadence that feels harder for long periods? Seems unlikely. It is hard enough to do FTP intervals at the "most comfortable" cadence, why make it harder.
Good example of overthinking things:
http://www.slowstepcycling.com/index.php?option=com_content&view=article&id=59:big-gear-work-to-increase-riding-power&catid=42:articles&Itemid=65
My notes:
Bottomline:
In my experience, focusing on cadence is a tool used by athletes without power. In general, you tend to ride at higher watts at lower cadences so...grinding a big gear could be used as a tool push higher watts. But once you have power and are able to line up power, HR, cadence, RPE, and speed, you can see there is a lot more going on.
Int@ 2mins Cadence Speed Torque Heart Rate
1 81 16.3 217 129
2 91 18.4 199 129
3 102 20.6 176 134
4 82 18.7 212 132
5 92 20.5 196 130
6 101 22.7 177 135
7 80 19.2 217 132
8 91 219 186 133
9 102 24.5 175 136
10 82 21 211 132
11 91 23.2 196 132
12 101 26 176 136
13 81 22.2 216 131
14 91 24.9 197 132
15 102 27.9 176 136
16 82 24.2 211 134
17 91 26.8 197 134
18 102 30.4 175 136
At the higher cadence of 100 the HR does go up, ot so much at 90. The speed really goes up with each increase in either cadence or gearing, but the Wattage stays the same. Thoughts anyone? Dave
Feedback
Vince
Dave,
If I interpret this correctly, you used the computrainer in erg mode set at 210? If so then speed will vary quite a bit with cadence and gearing, but it isn't relevant. By increasing cadence and gearing, in essence you are trying to pedal harder (put out more watts), in ergo mode though the CT has to hold you at 210 watts so it does this by loosening the pressure on your back wheel, making it turn easier (and therefore faster). In the real world, on the pavement, a watt is a watt and will generate the same amount of speed whether it came because you turned the pedals faster (increased cadence) or harder (increased gearing). Does this make sense?
For my test, I agree with Rich and Chris, I'm not aiming for a magic cadence of 90, I just seem to end up there most comfortably when I need to hold FTP. I seem to get tired faster when I push a bigger gear at lower cadence or if I spin an easier gear even faster.
Vince- That is a bigger difference than I have but I definitely pedal lower rpm outdoors. Outdoor cadence = 88-90, Indoor cadence = 80-82. Plus, my FTP is so much lower Indoors. 248 Indoors vs 268 Outdoors. Maybe mental but just can't seem to hold the watts indoors.
You are not alone. I think there is just a big watt sucking vortex built into every trainer that steals watts before they get to your PM computer.
That's my story anyway, and I'm sticking to it! 
Just wait till the calendar starts stealing your watts (especially at the high end). The years have humbled me, and I accept every single watt my CompuTrainer can find for me - hope I don't end up in double digits someday.