Currently I workout as follows:
6 hours a week where
70-90 minutes of cardio in total.
No bench press or squats (the why part isn't relevant here)
Isolated muscle workouts for upper, abdominal and lower bodies
60-70 pullups in total per week
I'm 5'6", 38 years old, male, with about 23-25% body fat .
I'm soon going to start Muay Thai about a total of 2 hours per week (2 one hour sessions). Being a busy professional, I will only be able to do my normal workout 3 to 4 hours a week, no more; but I'd like to keep my muscle muss (i.e. appearance) more or less the same, even though I don't mind losing a bit of muscle strength (so to give an example, I can do isolated tricep exercises with 35kg (~77lbs) about 15 reps, and leg press with about 180 kgs (~395lbs) about 15-18 reps. If these figure decrease a bit but not significantly, I'll be okay with it. My importance here is about i) looking the same and ii) of course, get at least half good at Muay Thai, but the latter won't help me much grow muscle.
Things that must remain the same: I must specify that I don't want to add bench press or squats, but open to restructuring other parts of my workouts. I think I'll at least want to run 60 minutes a week.
Is there anything I could do to achieve my goal? I'm thinking of a more protean heavy diet - do you think that'll help me achieve my goal i)? Is there a workout plan should I follow to prevent muscle loss?