Can someone explain the differences between “power” and “perceived exertion” other than watts can be shown on Powertap? Getting ready to do some winter workouts and I’m using three devices, Spin class, Expresso bike and Cycle-ops Fluid with Spinervals DVD’s at home.
Spin bike and Expresso trainer at the gym both give watts. No Powertap at home so it’s just “burn” and “gears” on the fuild. But I honestly feel a lot more “exertion” on my trainer at home than I do running 350 watts climbing in a spin class.
How do I make sense of the two w/o selling out $1000 for a PT, which of course would end both power an PE as my wife would shoot me DEAD. :o)
Can someone explain the differences between “power” and “perceived exertion” other than watts can be shown on Powertap?
Power is objective - hard, concrete data that you can see and compare.
Perceived exertion is subjective - how you feel on a given day, which can be vague, varies from one person to the next, and can be influenced by other factors.
On your trainer, use your speedometer as an indicator of your work effort, because there are no winds, hills, downhills, etc it’s good.
Provided you maintain consistent tire pressure, temperature and tension and you use the same trainer and tire. Otherwise your results can vary a lot for different sessions. You have to be meticulous with the setup.
Speed sensor on the rear wheel is the poor man’s power meter.
On your trainer, use your speedometer as an indicator of your work effort, because there are no winds, hills, downhills, etc it’s good.
Provided you maintain consistent tire pressure, temperature and tension and you use the same trainer and tire. Otherwise your results can vary a lot for different sessions. You have to be meticulous with the setup.
Speed sensor on the rear wheel is the poor man’s power meter.
"Speed sensor on the rear wheel is the poor man’s power meter. "
That’s pretty much where I am. Starting out riding in my 40’s so I got lots of kids expenses and college to look forward to. My hobbies fall pretty low on the priority list for the next 10 years or so. Just trying to figure out how to maximize what I currently have available to me.
I did buy a trainer only wheel/cassette so I’m using the same gearing, TP (100 psi) and 2.5 turns according to CO’s rec. each time. Only variable is the temperature in my garage. But wouldn’t that be an issue on the open road as well for a PT?
Some power meters have temperature correction algorithms, but I don’t think PowerTap does. So yes, it would only be accurately near the temperature for which it was calibrated. No idea how significant this error can be.
Fluid trainers are particularly sensitive to temp. The fluid becomes less viscous as it is heated resulting in lower power at a given speed. Not only should you try to have constant air temp, but you should warm-up for a consistent amount of time. For my CycleOps Fluid2, 30 minutes before intervals seems to suffice.
If you have no experience with an accurate real powermeter then this comparison is rather pointless. I was working my ass of on an exercise bike at the gym just to see what it says and I was putting out about 80 watts, they are not scientific instruments.
Many very accomplished athletes reached their potential by reading perceived exertion, so don’t get wound up about it. A heart rate monitor would be a pretty affordable way to connect between the separate training environments, with some obvious caveats. A power meter is a great thing but it has become too fashionable to downplay the value of plain old hard exercise.
In some ways PE has some advantage because on an off day you can get psyched out of doing your planned routine because you aren’t hitting the numbers. One school of thought says to bag the workout if you can’t hit the intended power numbers while another says that all training (provided you aren’t suffering from over training) is valuable and productive to create adaptations. It takes a bit of mental fortitude to soldier on through a workout when your power meter says you suck today. If it just feels hard then you get what you expected and aren’t thrown off your game.
The fluid becomes less viscous as it is heated resulting in lower power at a given speed.
fluid trainers require more power at a given speed when they heat up, not less
Come to think of it, you’re right in the case of the Fluid2. But I’ve experienced fluid trainers with both behaviours (i.e. more/less resistance as they heat up). This highly scientific article seems to confirm:
When** some **fluid trainers heat up, the resistance fluid becomes less viscous and creates less resistance per revolution.
There’s no question that fluids become less viscous as they warm, but there must be other factors that influence resistance. Maybe impeller design?
The term “thermodynamically neutral” is not really accurate, it’s just a fancy way of saying that the fluid in the KK trainer doesn’t change as much as other fluids (like peanut butter or motor oil). It still changes viscosity with temperature, as shown in the graph below.
This graph shows the power (solid purple) and speed (blue line) plotted against time for a workout done on a KK fluid trainer initially at about 15 C/60 F. Look at what happens in the first 5 minutes - power stays approximately constant, but the speed creeps up.
The good news is that it basically stabilizes after 5 minutes, and the change in power really isn’t THAT much.
