marclpz not sure why you would expect it to show anaerobic impact Z4 is not anaerobic. You'll only get anaerobic effect when you train with hard intervals or similar - where you are pushing yourself repeatedly into oxygen debt then recovering then pushing again. I've found it hard to get a high figure - but for example may last run gave me 3.0 Aerobic and 3.1 Anaerobic. That was 10 min easy run warmup 8 x 200M really hard at 5:15 to 6:15 pace (very hard for me :) ) with 400M jog recovery between each 200 then 10 min easy run to warm down.
