Well, 'Do I continue at all, in light of Real Life?' is obviously a personal question that would need to be considered internally.

But if the decision to continue is made, I can think of a couple of ways that 'Lifeforce Manipulation' can be used to handwave the issue.

Option 1: The knockout blows we've seen, probably in fact all the strikes delivered by 'normal' street fighters (Though, uh, not Decapre), aren't just, possibly not even primarily, about physical impact. Instead, all of them (rather than just the flashy attacks) carry a 'ki charge', introducing foreign energy into the target in an effort to cause an (ultimately harmless) bluescreen shutdown. This would actually neatly explain the games' lifebar mechanic - the ultimate crash-unconsciousness could only come if the target's ki was sufficiently weak relative to the attacker's, either naturally (a normal person) or via a full fight's attrition. Fighters probably know how to throw purely damaging blows, but choose to rely on the ki effect for basically friendly matches.

Option 2: Direct development and manipulation of ki reinforces the body's healing mechanisms, letting trained ki-users genuinely regenerate after a concussion in ways that normal people just can't.

Option 3: Both.

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Iä! Iä! Moe fthagn!