. . . you must hasten to oppose pernicious pride of mind, before it penetrates into the marrow of your bones. Resist it, curb the quickness of your mind and humbly subject your opinion to the opinions of others. Be a fool for the love of God, if you wish to be wiser than Solomon: 'If any man among you seem to be wise in this world, let him become a fool, that he may be wise' (I Cor. 3:18).
Muscle cells strengthen in response to intense exercise - whether you're 18 or 88. But the intensity is what's lacking in most people's workouts. And there are doctors who'll give you the advice, "Well, don't push it. "