I find a lot of benefit in two different low cadence exercises:
1) Up to an hour at a steady cadence near 70 and HR in high zone 3. This should be done without breaks if possible on the trainer, rollers, or on flat or gently rolling terrain. Once or twice a week for 3 weeks. Do this before attempting Muscle Tension Intervals.
2) Muscle Tension Intervals - sets with 10 - 15 minutes at 50 cadence, with half the interval time as rest period. These must be done in the saddle with no upper body movement. Do a set of 3 twice a week for no more than 3 weeks. Try to find a long hill with an even grade. Choose gears that will trash your thighs by the end of each interval. HR will be in high zone 3/ low zone 4. This is an early season workout.