How about self damage in form of rare hitpoint losses (out of the hat: 3% chance on normal strikes, 10% on criticals - and some maximum of damage gained trough this system. As your limbs get too damaged you would not use them anymore for attacks - thus player health sets boundary for prolonged use of these skills?
But - hitting enemies with unprotected arms/legs would cause often SOME pain. Chance of pain is initially something like 40% per hit, but this one would be capped too to maximum of say - 20 pain points overall from strikes. Also the chance to get more pain points from strikes decreases (you get used to) so the chance gets smaller for each additional point, like:
40% chanse to get pain per hit at pain 0
30% chance to get pain per hit at pain 1
25% chance to get pain per hit at pain 2
20% chance to get pain per hit at pain 3
15% chance to get pain per hit at pain 4
10% chance to get pain per hit at pain 5
etc etc etc…
You could reduce this pain by using gloves/paddings but this would affect the damage delivered too.
Also, the gear youre using would wear out sooner or later the more you punch and kick stuff (same chances as HP damage to bare hand). So you could not use this thing forever even when padded fully, each level of damage to equipment would mean 25% more chance that strike affects your hand directly. Having “reinforced” gear would eliminate one level of damage…
Maybe this would reflect the “self damage” aspect of MA? Maybe not really realistic, but gameworthy maybe?