Grip
Grip Strength, Handgrip
noun
Your grip power is your grip, or more specifically your grip strength or handgrip.
This is a jukugo word that uses the on'yomi readings of the kanji. You should be able to read this on your own.
自分の父親なんだから、善意に解釈してあげるべきよ。例えば、年を取って握力が弱っているせいで、あなたのビンテージのバカラのグラスを割っちゃったんだ、っていう風に。
He is your father so you should give him the benefit of the doubt. His grip has gotten worse with age and that’s why he dropped your vintage Baccarat crystal glass.