Isaiah 40:29–31

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

(ESV)