Since you were a fighter, I have a question how did you fit in explosiveness training when you were training muay thai? I haven't trained in a legit gym since July of 2017, and am just getting back into it in 2 weeks. So if you could answer that question that would be nice.
Lol, thread hijacked xD
Jk, iz kool.
Short answer: I didn't.
When I was training (first boxing, then kickboxing and finally MMA), I just did a shit ton of bagwork. On non-sparring days, I'd do 12 to 15 rounds on the bag, full power and going all out. Then I'd do 2 or 3 rounds of shadow boxing with 2kg dumbbells.
In a matter of weeks, my speed and explosiveness went up exponentially. I was landing anything I wanted in sparring due to sheer speed.
Many people now seem concerned with plyometrics, powerlifting and other such side-activities which are claimed to make you faster... honestly though, I did none of that and went from not being able to land a single cross in sparring due to being slow, to being the fastest guy in the gym for my weight (75kg). Lifting always destroyed my mediocre cardio and left me way too tired for specific training.
The more sport-specific the exercise, the better. Bagwork is as specific as it gets. You punch and kick things in kickboxing, so you might as well get good at it by punching and kicking as much as possible with speed and power.
Aside from that, I would do sprints once a week and a longer run once, mixed with push ups and pull ups.
As you see, 80% of my training was either sparring or bags or pads (specific to my sport), and the other 20 were to fill up time and keep active during the 'rest' days. I would have been equally good without the sprints and bodyweight exercises to be honest.
To recap, my advice is do a lot of bags on your free days, focusing on hitting it with power and speed (always wear wraps and go all out). Do it 3x a week and you should see results in two weeks.
Now if your goal is to be rounded athletically (have general strength, speed, agility and endurance), then just do it in cycles. 6 weeks of strength training only, then 2 or 3 weeks of running, sprints, long distance, cycling, bags to build up cardio (and only focus on cardio), then dedicate yourself to muay thai with a solid physical base for a few months, then do another cycle like that. A lot of guys did that. There's mpre to life for most ppl than fighting. A lot want to be ripped, or go do triathlons etc etc so they try to fit these other things in.
I never did, just stuck to fighting and it worked well.
Depends on your goals. Have a goal in mind and be goal-specific in your training.