1 Samuel 17:39

Verse 39. I cannot go with these] In ancient times it required considerable exercise and training to make a man expert in the use of such heavy armour; armour which in the present day scarcely a man is to be found who is able to carry; and so it must have been then, until that practice which arises from frequent use had made the proprietor perfect. I have not proved them says David: I am wholly unaccustomed to such armour and it would be an encumbrance to me.