Adelle Davis in her books claimed that too high a heat makes
meat tough -  She advocates slow cooking.

    Also  she has a recipe to boil eggs without turning the
yolk green.    :::::Put 4 eggs in one quart cold water.
Heat until water is at full boil.  Remove from heat  as soon
as boiling is reached.   Let stand in the hot water for 10
minutes(?)   This of course may need adjusting for altitude
and size of egg and temp of your cold water.
> ?
>
> Properly cooked, meat is not tough. Steak can be a bit
tough because it is
> briefly cooked (if you like steak rare as I do) and you
are chewing through
> the connective tissue.
>
>