Stronghold - Ok, what do you do improve it beyond running and circuit training?
Depends on which training cycle I'm in. Typically I do low base aerobic work about 3x per week with my HR around 130bpm. Then I also do bjj 4-5x a week where we have about 6x6 min rolls at the end of each class. Plus strength training thats my "general maintenance" chilling out training. It keeps me in a good general shape, my VO2 max is about 55% which isnt too bad for my age.
If I am stepping it up or in the final 6 weeks before a competition that I'd like to peak for, I will usually drop the aerobic stuff to 1-2x per week and then add in 2-3 supplementary anaerobic sessions.
the programming for these sessions vary. Some are continuous power output for longer intervals and others are like a 1:2 work:rest ratio of short sprints like 100m, and cluster them into 6min rounds or so.