We are going to work with training that varies between distance and time.
Remember that your HR is based on 220 - age. So you will be able to train within the desired zone.
Types of training:
Fartlek - You will have pace oscillation (Fast and Slow)
Interval - Generally on Z4 or Z5 with rest stopped.
Continuous / Aerobic / Long Running - Running generally in Z2 / Z3 continues and without stops.