I've had a few people ask me how useful isolation exercises are for mixed martial arts. Sans a few, I'm going to have to say that they are wholly and inarguably useless. There is almost no benefit to be had from isolating a single muscle. MMA requires full-body functional strength, and isolation exercises will not help you train that.

If you absolutely insist on doing isolation exercises, there are a few that will have some utility in MMA. The first that I recommend is the standing barbell wrist curl, which will help improve your grip strength--this is important if you want to excel in grappling. While your grip strength is trained in almost every compound exercise, it won't hurt you to supplement it. The other isolation exercise that is somewhat useful in MMA is the dumbbell curl. This has less utility than the wrist curl, but it will help you avoid certain submission holds, including arm bars and kimuras (from some angles.) While I don't really recommend spending your time doing curls, they will help in some areas of MMA.