‘The Lord is my strength and my shield, my heart trusts in Him and He helps me.’ Psalm 28:7
From what we learn from the Bible, King David was a strong upright warrior. His body had been honed on the fields of Bethlehem as He cared for his father’s sheep. Shepherding was no job for a wimp. Although he defeated Goliath by the might of God and not solely his own strength, he was growing from a lad to a strong man. As a king in those days he would have needed his physical might to overcome his many enemies. Then his years of constant flight would again have called on his physical resources.
Throughout all his problems we learn from numerous psalms that he didn’t rely on his own power, he continually called out to God for strength. He knew it wasn’t his might, he got this prowess from God who was a ‘very present help in time of trouble.’