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On second thoughts, KGB Kakuzu's point is probably wrong because Tsunade always maintained some chakra to keep her youth even in dire situations. Right
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, Sakura's punch
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even though in the beginning of Shippuden she could send them flying so WA Sakura was definitely restricted by constantly gathering chakra in her forehead. The more chakra that is being restricted, the less chakra is flowing through the brain which would mean the brain has less energy.