It’s all about how we make power on the bike.
The formula to calculate power is (Power = Torque times Cadence or speed). In class when we are using an ERG mode or blue block workout the computer program is controlling the power on your trainer based on a percentage of your FTP. So if the power is fixed or not changing when you slow down or speed up your cadence what changes?? The answer is Torque!! With the power fixed a high cadence will decrease torque or give you a lighter feeling in the legs and with a lower cadence, the torque will increase or produce more tension in the legs.
Outside real cadence (ORC) refers to the fact that outside we all climb or ride at a certain cadence that is comfortable on the flats or climbing. For most this is in the range of 75-90rpms outside. We use our gears to keep the strain on the legs comfortable but when we hit a hill and the power goes up generally we settle into our Outside Real Cadence and deal with a little more tension on the legs. If we have enough gears we may be able to keep the tension pretty light but eventually, on steeper grades, we run out of gears and need to use muscular force to help us climb the hill.
Inside Comfortable Cadence comes from having a fixed power as I explained above and then riding a faster cadence to take the pressure off the legs or reduce the torque. Riding a faster cadence will also increase the cardiovascular demand, which is a great thing to train but without training the strength in your legs, the amount of power you can produce outside will be less.
To improve more for outside riding it is important to know which system to train, using your ORC for longer efforts at Sweetspot or Threshold will increase muscular force or strength to apply outside.