Missing HR Target Zones

Good afternoon,

I have done 2 of your training programs. They are great.

However, both times I found that in the last 3rd of the program I found it increasingly hard to reach Zone 3 and Zone 4. That is, I would have to peddle like crazy to get my gear rate up and it was often nearly impossible to keep it in the right zone.

Was I overtrained perhaps? I stuck closely to the workouts but often felt strong and would do 15% above the specific objective. I use a HR monitor but a power meter.

Was I lacking in muscular power compared to HR/cardio development? That is, my HR/cardio showed great improvement (which was true) but this did not kept up with/ bifurcated from relatively less corresponding improvements in muscle power? So in short my hear got stronger and I could not then generate enough power to the pedals to push my new, stronger HR up?

Would a solution be weight training?

What training program would you recommend with this background?

Any other thoughts?

Thank you for your time,