This is highly dependent on your trainer and the gearing on your bike. For example:
- If the step requires an increase of 10 watts, you may need to just add 5 rpm cadence, because a rear shift might result in a 20-30 watt increase if you hold the same prior cadence.
- If the step requires an increase of 100 watts, there’s little chance you can hit that with a cadence change, so a one shift or more would be required.
You have to learn your specific setup through experimentation and see what amount of steps mean for you. Also, you can keep in mind the functional cadence range you’d like to cultivate, and pick cadence or shifting based on that.