During the off-season, which incidentally coincides with the bulk of my trainer rides, I usually tend to structure my workouts around HR, not power, to build my base aerobic fitness. A typical workout for me looks like the following:
- Start with a 10-15 min warmup phase, gradually building up to the target HR (e.g. 145 bpm)
- Maintain HR in the 140-145 range for the duration of the main set
- Short cool down phase, with HR going down towards normal levels.