training in heart rate zones: I can't stay in 2....?

Please confirm that 175 is your LTHR and what zone type you are using? Also use the reset on your Running zones as the percentages can drift. Also confirm that the zones match on your device and in GC.

For me zone 2 is easy running but if I run after a stressful day, or too much coffee, that same pace will be at the lower end of Z3.

If you can't keep your HR below 156 during a run, you probably haven't trained your aerobic system enough. As far as I can read, that is quite common among runners. They train their anaerobic system but forget their aerobic system. Which is a pity, because the aerobic system is important in any race lasting longer than a few minutes.

The anaerobic system is fueled by glycogen, and the body only stores a limited amount of glycogen. The aerobic system is fueled by fat, and the body has plenty of fat to burn, even if you are quite skinny. When people talk about hitting the wall during a marathon, it is because they ran out of glycogen, and their aerobic system was not developed enough to continue on fat.

If you want to train your aerobic system, a lot of coaches seem to prefer long duration training at a quite low heart rate. In the beginning, you may not be able to run at this heart rate - just as you experienced. But if you stick to it, perhaps doing a lot of walking every day, your aerobic system will get stronger, and after a few months you will be able to run slowly at a low heart rate. After a few months more, you will be able to gradually increase your running speed at the low heart rate. This will mean that you have developed your aerobic system.

Disclaimer: I am just an inexperienced runner. But I have been doing a lot of reading and exercise during 2018, and I have improved from really, really bad performance at low heart rate to a somewhat acceptable performance at low heart rate.

AllanOlesen67 I think you're confusing two things here. Anaerobic activity occurs when the body's ability to extract and use oxygen is outstripped by the need for energy to power the muscles This results in glycogen being broken down without use of oxygen and so generating lactate This lactate causes the burning sensation experienced in the muscles by sprinters etc. When lactate levels pass a certain point then muscle ability to contract drops off drastically so anaerobic activity can only occur for very short bursts.

Sprinters training increases their tolerance to lactic acid and so lets them function longer anaerobically.

You're right about glycogen supplies being limited and the wall in a marathon and the way to increase the body's efficiency at burning fat is generally believed to be by long slow activity. Some recent schools of thought also believe that hiit can promote this too. Walking or walking and running is certainly a good way to get the low intensity training and keep you in the right HR zones.

Please confirm that 175 is your LTHR and what zone type you are using? Also use the reset on your Running zones as the percentages can drift. Also confirm that the zones match on your device and in GC.

For me zone 2 is easy running but if I run after a stressful day, or too much coffee, that same pace will be at the lower end of Z3.

175 is indeed my Lactate Treshhold. Zones are calculated by Heart Rate Reserve calculation

Thanks for your insights. I was thinking my HRZ2 could be miscalculated as I run with the same effort in zone 3 as my husband does in zone 2.... subjectively speaking.