Sorry for silly format as I'm typing on my phone. Tl;dr at bottom.

So then, you're sparring with the Captain of beatdowns on your long slog to power level your experience up so you can deliver him a can of sweet, sweet whoop ass first hand. You select to combat practice with the Captain And you manage to beat him! (Yay) but he also takes down your health halfway or so in the process.

Your immediate thought may be to rush home and sleep it off or bandage yourself or even use a potion. Nay! All you need to do is immediately talk to the Captain and request to practice master strikes. Upon starting this, the good captain (I figure) takes pity on us and refills our health and stamina gauge to full! (If you are exhausted from lack of sleep or hunger this does not go 100%)

Quickly finish the master strike class and restart a combat practice round with renewed health and give him another serving of fresh whoop ass since he seems so keen to have it.

Extra tip: (im sure most are aware of this but it may benefit someone reading this) it took me longer than I care to admit to make the connection that Captain Bernard is wearing plate armour, so maces easily destroy him whereas swords definitely take much longer.

tl;dr if low on health after combat practice with captain Bernard, ask him for master strike lesson and he refills health and stamina for you.