Maybe Hungarian arms are not a part of the body. The sentence doesn't make sense to me.
Makes senses to me in English. Although strictly speaking an arm is part of the body; the body can also mean the trunk ie neck to groin.
Is this like the Hungarian equivalent of "the spirit is willing but the flesh is weak"?
That one is from the Bible:
Watch and pray so that you will not fall into temptation. The spirit is willing, but the flesh is weak. (Matthew 26:41)
Vigyázzatok és imádkozzatok, hogy kísértetbe ne essetek; mert jóllehet a lélek kész, de a test erőtelen. (Máté 26:41)
Erőtelen is a bit archaic here, modern Hungarian would be erőtlen. (It mean powerless.)