Watts: Controlled threshold, Z4-
Heart Rate: Threshold HR, Z4

Strive to maintain a steady load and let the HR build up under load. The HR should increase over the intervals but do not enter. Z5.

Borg: 15-16
During longer intervals, the effort should initially be experienced as 15. At a steady load, the effort will build up to Borg 16.

Z4- sessions (controlled threshold) are performed as longer intervals or sustained tempo training. Breathing becomes forced into the training. The first few minutes may even feel too easy, but the load and HR build over the interval.

Use a cadence that gives the best speed with the lowest HR/effort, unless other rpm is instructed. This can be difficult to test, but with power measurement on the test bike, you will notice quite quickly which cadence gives the lowest HR and highest power for the longest time.

If you don't have a power meter, you can feel the load and effort that builds up to Z4 HR. You can also test if you have a speedometer on your bike outdoors . Ride a certain distance at the same speed at different cadences and compare fatigue (Borg) and HR.

The main purpose of controlled threshold is to increase your muscular endurance/aerobic adaptation in a time-efficient session.

Watts: Low-intensity Zone, Z2
Heart Rate: Low-intensity zone, Z2
Borg scale: 9-13

Purpose:
+ Develop basic endurance and muscular aerobic adaptation.
+ Improved use of fat as an energy source.
+ Getting used to the sport specific long term load.

Watts: Moderate Zone, Z3
Heart Rate: Moderate Zone, Z3
Borg Scale: 14-15

Purpose:
+ Base training
+ Moderate intensity primarily gives you a time efficient way to increase your muscular endurance/aerobic adaptation.
+ Get your body used to steady, high speed.