Knowest thou not, or hast thou not heard? the Lord is the everlasting God, who hath created the ends of the earth: he shall not faint, nor labour, neither is there any searching out of his wisdom. It is he that giveth strength to the weary, and increaseth force and might to them that are not.  Youths shall faint, and labour, and young men shall fall by infirmity.

 But they that hope in the Lord shall renew their strength, they shall take wings as eagles, they shall run and not be weary, they shall walk and not faint.

Isaiah 40:28-31