Isaiah 40:29-31
29He giveth power to the faint; and to them that have no might he increaseth strength.
30Even the youths shall faint and be weary, and the young men shall utterly fall:
31But they that wait upon the LORD shall renew their strength; they shall mount up with wings as eagles; they shall run, and not be weary; and they shall walk, and not faint.
(KJV)