Endurance Program for Running

Endurance Program is based on different program levels, and it helps you build running endurance. User's program level is defined by answering some questions regarding user's physical activity or by analyzing automatically user's training history in polarpersonaltrainer.com. Training history based definition can be done if user has enough training history from the last three months in polarpersonaltrainer.com.
General programs are compiled of 4 weeks long training modules. Training module in level 1 is the least demanding and the module in level 20 is the most demanding. Steps between 1-20 are linear, which means that user can improve his/her fitness step by step (for example from level 7 to level 8 etc.) Training modules and user's training activity are linked together so that training modules gets more challenging as user's training activity increases (also less challenging when user's training activity decreases), see figure below:

Figure 1. Endurance programs has 20 training modules. Each module is 4 weeks long.
Beginner (levels 1-6):
The objective of the Beginner –level programs is to accustom your body to endurance training to enable you to run longer runs in the suitable intensity. The training volume is relatively low and the training sessions are basic and long runs. If you want to prepare for a marathon or half-marathon, you need to proceed to higher levels by following this program carefully.
Moderate (levels 7-12):
The objective of the Moderate –level programs is to accustom your body to higher levels of endurance training to enable you to run even longer runs. By training according to guidelines, you will get fit enough to keep your heart rate under control and stable when running. The program consists of 3-5 training sessions per week including basic, long and interval runs. Compared to advanced levels, moderate levels do not include tempo runs that are aimed to develop resistance to fatigue at higher speeds.
Advanced (levels 13-20):
The objective of the Advanced –level program is to develop endurance running performance close to your own maximum level. The program consists of 5-6 training sessions per week including basic, long, interval, and tempo runs. This program requires personal care and awareness to ensure optimal recovery, sleep and nutrition. Also, a personal coach could point out your individual strengths and weaknesses, which could be helpful in fine-tuning the program.
Long Run The target of a long run is to build basic endurance by running a long distance. In the beginning of the long run, the intensity target is zone 2. In the beginner and moderate levels, zone 3 is included towards the end of the session. Running in zone 2 builds endurance by developing fat oxidation capability. Running in zone 3 in the end of the session (included in the beginner and moderate levels) also builds up resistance to fatigue in marathon speed.
Basic Run Basic run is the most typical endurance running session. The duration of the basic run is normally around one hour (distance 7 – 15 km). One phase of the basic run is always run in zone 3. Before the phase in zone 3 starts, the higher program levels also include running in zone 2.
Easy Run Easy run sessions are similar in duration as the basic run sessions, but easy runs are run in zone 2 only. There are several reasons to keep the sessions easy: good runners can run relatively fast even having low heart rates – they can effectively build up total training load / weekly mileage and develop fat oxidation during training, while they can still ensure recovery and readiness for the upcoming high intensity sessions. Good recovery is achieved because muscle glycogen is spared and hitting forces/impulses to legs are kept at a low level.  
Interval Run Interval runs develop speed, aerobic and anaerobic capacity, and resistance to fatigue at 3-10 km race speeds. Keeping short recovery periods between the sprints allows more training at high speeds. The sprint periods are recommended to be done in zones 4 and 5, and the recovery periods in zone 3. Zone 3 is usually low enough to remove lactate, but note that you should also use the low end of zone 3 during the recovery periods. In particular, if your target is to develop maximal speed for short endurance distances, it can be beneficial to lower your heart rate even to zone 2.
Tempo Run Tempo runs develop aerobic capacity and resistance to fatigue at 10 km marathon race speeds. The tempo parts are recommended to be run in zone 4 in order to build resistance to fatigue at marathon and half-marathon speeds and to improve speed in the lactate threshold.