Isaiah 40:29-31

29 He gives power to the faint; and to him who has no might he increases strength.  30 Even the youths shall faint and be weary, and the young men shall utterly fall:  31 but those who wait for Yahweh shall renew their strength; they shall mount up with wings as eagles; they shall run, and not be weary; they shall walk, and not faint.