resting during cycling intervals

For longer rest intervals, I try to keep the same cadence. So I switch to an easier gear. However, with this workout you only have 10 seconds. So just spin slower.

For me, both. A 20 second interval is going to super intense. I might do the interval at, say 100-110 rpm, and drop down to around 80-90 rpm for the rest. That's not really a rest if it's in the same gear, and if it does feel easy, then the gear for the interval wasn't hard enough.

I could see keeping the same cadence and shifting to an easier gear, but I don't see how you could make do with only a cadence drop, unless we're talking like 5 minute intervals where the intensity is lower.

I was just wondering the same thing today (or the opposite, I guess). Having just signed up for TrainerRoad and doing my first FTP test, I was wondering whether intervals of increased intensity should be done with higher cadence, different gear, or both.

I think it depends on the nature of the intervals that your doing and how you are defining hard. I work with a coach/trainer for cycling right now and the first thing we did was find my "Recovery Gear". During longer rests/recovery I fall back to this gear. There are a number of intervals in a session where like you said the recovery is shorter duration at which point the slower cadence is what allows you lower the heart rate.

The other thing to consider is what is the purpose of the intervals that your doing. Some intervals are designed to push you to Anaerobic Threshold repeatedly. As this is information that is being provided to me through my specific sessions I may be misinterpreting something but generally these shorter recovery intervals tend to be when we are working on getting to that anaerobic level.

a typical interval for this for me looks like

Hard Intensity 90-95 RPM for 2 minutes
Recovery same gear but 65 RPM for 30 seconds
Repeat 3-4 times
Recovery Gear 90 RPM 2 minutes
Next interval

Looking at the heart rate data you can see the heart rate climb steadily through each interval until you finally are at your MAX. The 65 RPM parts do see Heart Rate drop a bit but the next Hard intensity pushes it up passed the previous level