If you are training MMA, i suggest not to combine bodybuilding training with MMA.
They each have a different mindset and the workout will lead to different paths.
You will have problems in MMA if you train like a bodybuilder, and similarly you will have problems with gaining bodybuilding mass by following MMA routines.
Here's my suggestion:
1. increase your aerobic base. You can keep on running your 3 miles. I would suggest doing a moderate cardio for at least 30 mins, but include a 3-5 minute burst of sprints. Do the burst 2-3 times within the 30 minute period.
Incorporate bodyweight exercises as a means to help with your cardio. I can recommend a good calisthenic routine that works well for my clients to improve their cardio, just let me know.
2. After you have increased your aerobic base, this shows your body is in better shape to produce oxygen and deliver them to your muscles. At this point you want to work on your muscular endurance so that your muscles get used to processing the oxygen your heart pumps which you developed from your cardio training.
The next stage involves strength and explosiveness training, but this isn't part of your question. I want to be as specific as I can.
Again here's what you can do right now to increase your cardio base.
run 3 miles, and do 2-3min sprint burst within the 3 miles you run.
do this for 2 weeks. Then you need to incorporate a cardio routine specific to MMA. For this you need to have the ability to change levels, and not just running on your toes.
You can do this by running, then doing bear crawls, crab walks, alligator push ups, then resume running upright.
I hope this helps a bit. feel free to ask if you have specific questions.
I've been training in MMA for a while now. I took some time off and got into bodybuilding but I've been back to MMA for the past 5 months and my endurance is way lower. I did put on a lot of muscle which i know takes more oxygen to keep going but I'm struggling with my cardio lately. I started running and doing 3 miles and I'm dying to complete it. Before I could run 10 miles without gassing. Are there things I can do to get my cardio back or do I just need to keep running and training and it will eventually improve?