As someone that's been involved in the industry for so long I have seen hundreds and hundreds of excellent Runner show up to the gym only to get smoked on the mat. This was particularly noticeable at the high school level where excellent endurance Runners would often try their hand at wrestling. I had a severe motorcycle accident at 16 and was never able to run. I was also a super-heavyweight averaging around 20 to 30% body fat. My cardio was excellent as I routinely beat guys solely on my ability to outgas them on the mat I would swim and bike as an alternative (when injured) however I spend 99% of my time on the mat otherwise. When I took over my high school team from the original coach my athletes were shocked that I cut all running out of the program They were further shocked when they found out that they performed better without running whatsoever. I developed a saying that I still hold to this day....if you have time to run you didn't spend enough time on the mat today I firmly believe that grappling and MMA in particular have the highest cardiovascular demands of any athletic activity known to man.