As someone who have dabbled in chinese martial arts what they meant by 'crotch' is when you generate power for a punch or when you lift something up normally you'd contract your core muscles and the area around your anus and your crotch. It's all that area that you're concentrating on. For instance try coughing or throwing a punch-
a real punch-if you know what those are. Pay attention to which muscles are used when you do this. It's those areas that I've mentioned. In chinese martial arts developing this area is crucial for generating power or in karate, there's the hip thrusting technique for when you throw a punch. The same muscles are used to generate power. Since this is fantasy they're exaggerating and with a dose of stupid translating it made something that's suppose to be normal into something silly.
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