MMA and Boxing are endeavors that rely heavily on ones aerobic system. Take a 5k for example, an event that is largely aerobic, for most elite runners, it should take 14-16 minutes to complete. These runners are averaging upwards of 80 miles a week easily for a relatively short race. An MMA match is 15-25 minutes, a boxing match is even longer. In my opinion, fighting is largely an aerobic endeavor. I personally believe that pro fighters should easily be doing 40+ miles of running a week if they can handle it, the reason behind this is that runners on average can typically develop a much higher V02 max than rowers, swimmers, etc (cross country skiers are really the only athletes with a higher VO2 max than elite runners, but it's not common for fighters to do that).
The majority of a fighters training outside of the specific should be based towards developing an aerobic capacity. I would limit the anaerobic work to once a week. Something like airdyne bike for 1 minute all out, 3 minute rest for 8 rounds for the anaerobic work. Then one VO2 max interval workout like 800m*6 and then 3 long runs at 7-11 miles.
Fight specific aerobic capacity work can be something like hitting the bag for 30 seconds all out, 30 seconds rest and repeat for 18 rounds. However, that will not develop the endurance necessary for 25 minutes and it's hard to hit the bag consistently for 1 hour and 30 minutes, so easy paced long runs will be necessary.
